SCUBA AND NITROX SAFETY INTERNATIONAL OPEN WATER DIVER ENGLISH

Transcription

1 SCUBA AND NITROX SAFETY INTERNATIONAL OPEN WATER DIVER ENGLISH

2 flow chart go to SCUBA AND NITROX SAFETY INTERNATIONAL Dry Suit Diver Hovering Diver Orienteering Diver Night Diver Deep Diver Boat & Drift Diver EXPLORER DIVER 1 EXPLORER DIVER 2 EXPLORER DIVER 3 EXPEDITION DIVER -51m -170ft -170ft -51m -72m -235ft -235ft -72m -90m -295ft -295ft -90m Wherever You want to go, We can take you there! EXPLORER DIVER 1 NoLimits NoLimits EXPLORER DIVER 2 EXPLORER DIVER 3 EXPEDITION DIVER

3 SCUBA AND NITROX SAFETY INTERNATIONAL OPEN WATER DIVER COURSE

4 OPEN WATER DIVER INTRODUCTION SCUBA AND NITROX SAFETY INTERNATIONAL ACKNOWLEDGMENTS We wish to express our gratitude to all the persons and organizations that contributed to the creation of this training manual. All those that generously contributed hours of work that resulted in this modern training system. Too many to be named individually, but each generously brought their best to contribute to our shared passion of teaching SCUBA to others. The result, the creation of a manual, a labor of love, was made possible by the contribution of the advisory group composed of the many SNSI Professionals, completely dedicated to the education of scuba and the conservation of the environment. Furthermore, the manufacturers that also contributed beautiful photographic images and equipment advise. Following named in alphabetical order: Aqualung, Dive System, National Geographic Snorkeler, Oceanic, Scuba Pro and Tusa. Thanks again to all for your valuable time given to this project, dedicated to education, exploration and marine conservation. Than you for joining us in ensuring a better world for future generations. Open Water Diver SNSI English Copyright November 15th, 2014 Published by: SNSI by Umby Divers di Fulvia Lami Via C. Puini, 97 - int. 34a Livorno, Italia Phone: info@scubasnsi.com This manual is an integral part of a teaching system property of Umby Divers company. No part of this manual or the teaching system can be reproduced copied with any electronic or mechanical device including movies, radio, television, photography without prior authorization in writing from Umby Divers. Registered mark. Any reproduction, including partial, forbidden. Important Notice: This manual is part of a complete system, and no part including this manual, constitutes an SNSI Open Water Diver course. To become a certified scuba diver it is absolutely necessary to complete an entire course successfully and be evaluated and certified by an SNSI Instructor. 2

5 WHAT IS THE SNSI FAMILY? It s a way of being together and taking advantage of a common passion for the sea. Anyone, whether they are diver certified or not, can share in this opportunity to learn and enjoy time together. We consider ourselves a family, because our customers, our certified divers and friends comprise a diverse but dedicated group. We can depend on them to respond enthusiastically to our new ideas and initiatives. They, in turn, have confidence in us and feel free to share their ideas and feelings. Most importantly, we see ourselves as people and not numbers, regardless of how many certifications or how much experience we have. Of course, our favorite activities are those that include a tank and a body of water to explore, but there s no less enthusiasm when we offer activities such as contests, games and dry weekends that include divers and non-divers alike. We are eager to have the opportunity to learn new theories, and techniques, but equally excited to spend an evening together viewing recent dive trip photos. Scuba diving is an excellent way to get to know new and different people. Whether you re diving at a familiar dive site, or traveling to a new and unknown dive destination, you ll have the opportunity to establish more friendships than you ever imagined. Though we re spread far and wide, we can always connect through our home base our central headquarters. Through it you can get information about our latest initiatives; meet hundreds of passionate divers from beginners to experts, and receive advice and encouragement. You ll feel part of a group; people united by their love and respect of the ocean. This is a family that you ll love to belong to: Our family tree has a branch for everyone! INTRODUCTION OPEN WATER DIVER 3

6 INTRODUCTION OPEN WATER DIVER OPEN WATER DIVER DiveUpYourLife 4

7 CONTENTS CHAPTER 1: SNORKELING EQUIPMENT 1. Introduction The Mask 13 Choosing the mask Using the mask 3. The Snorkel 15 Choosing the snorkel Using the snorkel 4. Fins and Boots 17 Choosing your fins Fin kicking 5. Protective Clothing 20 Choosing your suit 6. Weight Systems 22 The weights Using the weight belt 7. The Snorkel Vest Placing your Snorkeling Equipment Entering the Water 25 Checking your weight Surface dives 10. Exiting the Water Summary 27 CHAPTER 2: SCUBA EQUIPMENT 1. Introduction The Buoyancy Compensator Device 31 Choosing the BC Using the BC 3. The Cylinder The Regulator 35 The first stage The second stage 5. The Alternate Air Source Underwater Instruments 37 The submersible pressure gauge The depth gauge Timing devices The compass The underwater computer 7. Using the SCUBA Unit Self Contained Underwater Breathing Apparatus 40 Assembling the equipment Wearing your Scuba equipment Entering the water with the Scuba unit The first descent Breathing underwater Exiting the water Dismantling the SCUBA unit 8. Diving accessories 44 Knife INTRODUCTION OPEN WATER DIVER 5

8 OPEN WATER DIVER INTRODUCTION Flag and floats Surface marker buoy The whistle Underwater lights Thermometer Tool box and spare parts The dive log Gear bag 9. Cleaning and Maintaining the Equipment Summary 47 APPENDIX TO CHAPTER 2: DIVING USING A DRY SUIT 1. Introduction Why use a Dry Suit Types of Dry Suits Characteristics of the Dry Suit 53 Wearing your dry suit The dry suit valves 5. What to wear under your Suit Dry Suit Diving Techniques 56 Dry suit concerns Practicing using the dry suit 7. Post-diving Procedures Cleaning and Maintaining the Dry Suit Summary 61 CHAPTER 3: THE PHYSICS OF DIVING 1. Introduction Breathing and Gas Exchange First aid for Breathing Ceisures Physical Condition and Diving Adapting to the Underwater Environment Effects of the Increase in Pressure Equalizing Pressure 73 The ear The sinuses The equipment 8. Effects of Decreasing Pressure The Human Body Underwater 77 Overheating and hypothermia Seeing underwater Sound 10. Making your Ascent 80 Normal ascent Using the Surface Marker Buoy Emergency ascents Alternate air source ascent Air Sharing Ascent Emergency swimming ascent Emergency Buoyant Ascent How to breathe from Free Flowing Regulator 11. Summary 85 6

9 CHAPTER 4: THE PHYSIOLOGY OF DIVING 1. Introduction Gas Partial Pressures - Dalton s Law Gas dissolved in Liquids - Henry s Law Nitrogen Narcosis and Decompression Sickness 93 Nitrogen Narcosis Decompression Sickness Prevention 5. First Aid and Treatment Summary on DCS The Dive Tables 98 What is "Doppler"? Dive Tables Terminology 8. The SNSI Dive Table Planning Repetitive Dives The Dive Computer How to use a Dive Computer The Computer after Diving Choosing a Dive Computer Safety Procedures 112 When using a computer 14. Diving at Altitude and Flying after Diving Summary 113 CHAPTER 5: NITROX OPTION 1. Introduction What is Nitrox? A little History How the Air is Enriched Nitrox Compatible Equipment Problems related to Breathing Oxygen at High Partial Pressure Diving whit EANx SNSI Safety limits for Using Nitrox Summary 125 CHAPTER 6: THE UNDERWATER ENVI- RONMENT 1. Introduction Temperature and Visibility Waves and Breakers Tides an Currents Underwater Life 132 Understanding Marine Habitats 6. The Principles of Classification 134 Marine algae Marine plats Spongers INTRODUCTION OPEN WATER DIVER 7

10 OPEN WATER DIVER Cnidarians Marine worms Molluscs Crustaceans Bryozoans Echinoderms Chordates Tunicates Vertebrates Fish Reptiles Mammals 7. Tropical Environments 147 Reef Zones A glance at reef life 8. Summary 153 APPENDIX: DIVE TABLES INTRODUCTION 1. U.S. Navy Diving Tables SNSI Dive Tables - Metres SNSI Dive Tables - Feet 163 8

11 FOREWORD Your first breath underwater is an experience that you will remember for the rest of your life. It will not only be easy and fun, but your successful completion of the course will result in you being awarded a passport to a new world. This license enables you to scuba dive all over the world. In the oceans, seas, lakes and rivers live a countless number of aquatic animals and forms of plant life that will astound you with their beauty. Meeting with a magnificent octopus or the discovery of a tiny nudibranch with its bright colors are events you ll never forget. But right from your very first dive you ll experience diving s greatest sensation of all: gliding weightlessly across a space of water, like an astronaut in space. The SNSI Open Water Diver course provides ideal basic training for plunging beneath the surface of the water and experiencing the fantastic sensation of living in another world. Thanks to modern diving equipment and techniques, you and your buddy will be able to enjoy exploring this new world of adventure and discovery in safety and security. We ve created this course for modern scuba divers: You ll learn to dive not only with traditional tanks containing compressed air, but also how to breathe a mix of air enriched with oxygen called nitrox. Our belief is that beginning divers should also be taught the countless advantages of diving with this simple blend. To earn your SNSI Open Water Diver certification you ll have to read this manual and answer the questions in the study guides at the end of each chapter. If you have trouble answering these questions, read the chapter again. To be awarded the certification you ll need to score at least a 90% on a 50-question multiple-choice test. If you choose the Nitrox option, there s a 70-question? exam. You ll watch a video that will show you how to perform all the exercises. Additionally, your instructor will demonstrate all exercises before you have to do them yourself. You ll repeat the exercises throughout the course until you re able to do them easily. Once you ve achieved this ability, you ll earn your SNSI Open Water Diver certification. This will allow you to dive to depths of up to 18 meters (60 feet) within the no-decompression limits, with a buddy who has at least the same level of certification as you. Have fun! INTRODUCTION OPEN WATER DIVER 9

12 INTRODUCTION OPEN WATER DIVER OPEN WATER DIVER All videos for SNSI Open Water Diver Course are available on You Tube SNSI Channel: 10

13 CHAPTER 1 SNORKELING EQUIPMENT 11

14 CHAPTER 1 SNORKELING 12

15 CHAPTER 1 INTRODUCTION Seeing, swimming and breathing are the three essentials for diving. Since we re entering a brand new world different from our natural environment, we need equipment that allows us to function in that underwater environment. Diving equipment is classified into: Watch the SNSI OWD Introduction Video -- Snorkeling equipment, which requires you to hold your breath and ascend to the surface as soon as you feel the need to take another breath. -- SCUBA equipment, when added to the snorkeling gear, includes a supply of air that enables you to stay underwater longer. By reading this chapter you will learn about the equipment that is used for snorkeling, and the basic rules on how to use and maintain it properly. THE MASK When you submerge your face in water with your eyes open, you get a blurred picture of the surrounding environment. This is because the human eye is designed to see in air. Because water has a different density than air, you can only see clearly underwater when your eyes are surrounded by an air bubble. Your mask creates this bubble of air around the eyes and this allows you to see clearly. There are various models of mask you can choose from, but each model has several essential features common to all masks. CHAPTER 1 SNORKELING 13

16 CHAPTER 1 SNORKELING Masks must: a. Cover the nose, unlike swimming goggles; b. Allow you to pinch your nose easily between your thumb and index finger to allow pressure equalization; c. Have lenses made of tempered glass, to prevent eye and facial injuries in case of accidental breakage (and foot injury if anyone accidentally steps on them). The mask may have a single front lens or two lenses set side by side at the same level. There are masks with side glass that increase the diver s field of vision. The optical characteristics of the mask can also be modified either by replacing the original lenses with corrective lenses, or by bonding two prescription lenses to the inside of the lens; d. Have a comfortable skirt made of rubber or silicone, which makes a water-tight seal; e. Have a bezel made of stainless steel or plastic, or another anticorrosive material that holds the lens or lenses and the skirt of the mask together; f. Have an easily adjustable strap. Another difference in masks is the volume of air inside, which may be low, medium or high according to the size of the mask itself. Low volume masks, with a smaller air space to equalize, are primarily used by free (breath-hold) divers. Masks with a medium to high volume are better suited to scuba divers, providing a broader field of vision. Finally, some masks have a oneway purge valve that makes it easier to clear underwater. Choosing the mask There are several different types and models of masks to choose from. To test a mask for proper fit, simply place it against your face without putting the strap behind your head. Then, with your head tilted backwards slightly, breathe in through your nose: the mask should remain in place when return your head to the vertical position. If the mask falls off, it means that particular model is not suited to the shape of your face. Once this first test has been passed, check that you can easily pinch your nose with the mask on. If you can, this mask should be appropriate for diving. 14

17 Finding the proper fitting mask Using the mask To put on your mask, place it against your face, then pass the strap behind your head keeping it high on the crown: a slight pressure should be all you need to keep the mask in place. All new masks are covered with a thin protective layer of lubricant that needs to be removed before use to prevent fogging. Wash your new mask well with a degreasing detergent, wiping the glass and the inside edge thoroughly. If this initial wash is done well, your lens will remain clear on future dives simply by using a de-fogging liquid prior to the dive. Now you are ready to have your first look at the fantastic underwater world. When you dive underwater, the pressure exerted by the water will press the mask against your face. You can equalize this pressure by breathing out a little air through your nose. This prevents an uncomfortable How to adjust the mask strap. mask squeeze. Certain facial movements, (such as smiling at the sight of a beautiful fish) may break your mask s seal and allow a little water inside. It s very easy to clear it: if you re on the surface, simply lift your head out of the water and pull the mask away from your face. If you re underwater on scuba, assume a vertical position, tilt your head downwards and press the top edge of the mask. Exhale slightly through your nose while raising your head and the exhalation will push the water out at the bottom edge of the mask. THE SNORKEL The snorkel enables a diver to swim on the surface and observe what is happening below without having to lift his head to breathe. It s a very simple device: a plastic or silicone tube with a mouthpiece also made CHAPTER 1 SNORKELING 15

18 CHAPTER 1 SNORKELING of silicone or rubber. Some snorkels have a one-way valve below the mouthpiece, which allows you to exhale and expel any water when the head is submerged. Choosing the snorkel The choice of a snorkel is strictly personal: it should have a mouthpiece that feels comfortable in your mouth, with a stiff tube that is an appropriate length. If it s too long, breathing is more difficult and, if it s too short, water could easily enter the tube. The average length of high-quality snorkels ranges from 30 to 40 cm (12 to 16 inches). The diameter of the tube is also important; the greater the diameter, the more difficult it is to clear the snorkel through exhalation. Using the snorkel Using your snorkel enables you to explore the sea bottom without having to raise your head to breathe every few seconds. It is most commonly attached to your mask strap on the left side of the head, using the snorkel keeper provided. When you put on your mask, the snorkel will remain suspended beside your face: all you ll need to do is put the mouthpiece in your mouth to look below the surface of the water and continue breathing. When you descend below the surface, the snorkel will fill with water. Once you ve reached the surface, exhale forcefully through the mouthpiece to push the water out of the tube in a spurt. You can also begin to clear it underwater as you ascend towards the surface by blowing a little air into the snorkel; the 16

19 air will expand on ascent and push the water out so you reach the surface with the snorkel already empty. Your snorkel is also important even while scuba diving. Using it while waiting on the surface for your dive buddy will save the air in your tank for the dive. Types of Snorkels FINS AND BTS Fins allow you to move in water with less effort. Many children for example, can swim with fins but have trouble when they take them off. Dive centers carry various models of fins, but there are primarily two types: full-foot fins and open-heel fins with straps. Full-foot fins enclose your foot in a soft rubber shoe. They are primarily used by snorkelers because they are lighter and more convenient for swimming on the surface. They can be worn on bare feet or with a thin neoprene sock. On open-heel fins with straps, the shoe is open at the back. The foot is held in position by a strap behind the heel. Scuba divers usually prefer this type of fin because they are easier to put on and take off. In addition, they can be worn over neoprene boots with a rigid sole, which help keep your feet warm and protected. They can also help with balance when walking on rough surfaces. Other differences in fins include: -- Length and flexibility: a fin with a long and/or stiff blade will require more effort and muscle to move through the water. Fins with a short and/or more flexible blade will usually require less effort. Open-heel Fin with Straps Full-foot Fin CHAPTER 1 SNORKELING 17

20 CHAPTER 1 SNORKELING Neoprene Boots with a Rigid Sole -- Size: Full-foot fins are normally sized like ordinary shoes. Open-heel fins are sized small, medium, large and extra large; the heel strap allows you to fine-tune the fit. -- Materials: Fins can be made of black rubber, thermoplastic material, polyurethane and other synthetic materials. Rubber fins are the heaviest and require the most leg effort. Fins made of synthetic materials come in colors, are lighter and more flexible and are usually preferred by scuba divers. -- Float: Fins may float (fins with positive buoyancy), sink (fins with negative buoyancy) or be neutrally buoyant (neither sink nor float). -- Vented fins: These fins have vents that make the upward kick easier while still retaining a firm downward kick. Choosing your fins If you are purchasing open-heel fins, you need to select an appropriate boot. We recommend that you purchase your boots and fins at the same time to be sure of the proper fit. The fins need to be the proper size: if they are too loose, they could cause blisters, while if they are too tight, they could cause cramping. Remember to take the stiffness of the fin into consideration based on your physical characteristics, Scuba divers should generally avoid excessively long fins that would be bulky to pack for travel. 18

21 Fin kicking Effective fin kicking will enable you to move easily in water, will increase your comfort and help you to admire and appreciate the beauty of the underwater worlds without getting tired. There are traditionally three types of fin kicks: the Flutter kick, the Scissors kick, and the Dolphin kick. -- The flutter kick consists in kicking your legs alternately; lowering and raising one leg first and then the other keeping your knee relatively straight. This kick is most commonly used in diving because it produces a strong movement and consumes little energy. -- The scissor kick consists in slowly opening your legs wide, with your chest at a slight angle to your pelvis and then closing your legs quickly. You can use this kick as an alternative to the flutter kick if you need to use different muscles or rest tired ones. -- The dolphin kick is done keeping your legs together, with a movement of the body that resembles the swimming movement of a dolphin. Whatever type of kick you use, it is important that the movements are broad and slow: a quick kick will increase your speed slightly but will consume more energy; bear in mind that to double your speed it will take four times the physical effort. When you kick on the surface while wearing SCU- Flutter Kick Scissors Kick Dolphin Kick CHAPTER 1 SNORKELING 19

22 CHAPTER 1 SNORKELING BA equipment, the most comfortable position is on one side or on your back. It is important that the BC (Buoyancy Compensator) is inflated so you stay comfortably afloat. PROTECTIVE CLOTHING When you touch a wooden or plastic object, then touch a metal object, the metal object feels colder, even though two objects are at the same temperature. The difference is the speed at which the two objects conduct heat; the metal object absorbs heat more quickly than the wooden or plastic object. Water absorbs body heat about 25 times more quickly than air. When diving, it is necessary to protect your body against this heat loss while in the water. The protective clothes used for this purpose are called exposure suits and there are various kinds, with different degrees of thermal insulation. Lycra suits protect the diver against abrasions, contact with stinging corals or sunburn but offer no thermal insulation and are commonly used in warm, tropical waters. Wet suits are made of neoprene, which is a sheet of high-insulation synthetic rubber. It contains tiny air bubbles that decrease in diameter when water pressure increases during a dive, thereby decreasing the thickness of the neoprene. This alters the diver s displacement and consequently his buoyancy (Archimedes principle, which we will discuss later on). Neoprene wet suits are the ones most commonly used for scuba diving. They are called wet suits because 20

23 they allow water in through the wrists, ankles and neck or face. This layer of water remains trapped between the diver s body and suit and is warmed by absorbing body heat. If the suit is the correct size, this warmed water remains in the suit, helping to maintain body temperature and slow heat dissipation. Neoprene wet suits ranges from 1/2 to 7 millimeters in thickness, come in several configurations: one-piece suits with a built-in or separate hood and a single zip which goes from groin to chin; two-piece suits with a jacket and trousers, or overalls and jacket. The hood may be built-in or separate, and the jacket may or may not have a zipper. There are also semi-dry suits, made of neoprene, which may be one-piece (or two-piece for those with separate hood), constructed like a wet suit but with a watertight zipper (normally on the back, from shoulder to shoulder) that limits water exchange. Dry suits completely seal the diver so that only his hands and head are exposed to contact with the wa- Wet Suits Under Wet Suit with Hood Gloves CHAPTER 1 SNORKELING 21

24 CHAPTER 1 SNORKELING ter. The boots, which are also dry, are sealed directly to the suit. Using a dry suit involves learning some additional skills, but allows you to remain warm in colder water. We will discuss this topic in the addendum to the following chapter, so you can learn to dive with one even as a beginner, if you choose. Choosing your suit The suit you choose depends on the environment in which you intend to dive. In tropical waters, a thinner neoprene suit can be used than in seas with lower temperatures. Remember that a suit with many zippers is easier to wear but allows more water in, providing less thermal insulation. Regardless of the suit, the most important consideration is correct sizing: it must fit closely to the body while allowing freedom of movement. It should not block your circulation or make it difficult to breathe. Dry Suit WEIGHT SYSTEMS A famous ancient Greek named Archimedes discovered a phenomenon that takes place whenever an object is immersed in a fluid. The fluid exerts a force on the object that varies according to the volume of the object. After many tests and experiments he formulated a principle that was named after him. Archimedes Principle states that a body immersed in a fluid is subjected to an upward force equal to the weight of the fluid that it displaces. In diving we will see just how important this principle is. We ll see that a man s body, when immersed in water, nearly always floats. In addition, our neoprene diving suit increases this floating effect. So, when you want to dive underwater, you must first overcome your natural floating ability and the buoyancy caused by your equipment. We can accomplish this by using weight to compensate for the buoyancy, making it easier to descend. The most common weight system is a belt to which lead weights are added. It is important that the belt have a quick release buckle so you can remove it with one hand. 22

25 The belt is normally made of nylon while the buckle may be plastic or metal. The latter, which is sturdier, is preferable. There are also weight belts with neoprene compartments in which the weights can be inserted and others with special pockets filled with lead shot. The Weights Lead weights come in different shapes and sizes: they usually range from 500 grams (1 pound) to over 3 kilograms (6 pounds) each. Some are covered with colored plastic and, although more expensive are more attractive, and less damaging if dropped on the bottom of a swimming pool or on the deck of a boat. Even more important is that they are less polluting than bare lead. Soft weights are made of nylon mesh bags filled with lead shot. Using the Weight Belt Once the weights have been attached, put your belt on by first holding the end without the buckle in your right hand. Pass it behind your back around your waist, then tighten it comfortably. To keep it from slipping off your hips, lean forward until the belt is buckled. It is important to learn how to release your weight belt quickly. First locate the buckle at your waist, then release it, moving the belt away from your body before letting go. This maneuver will give you immediate positive buoyancy if you are in deep water and will allow you to float easily to the surface. Belt with neoprene compartments and pockets filled with lead shot. BCs Integrated Weight Pockets CHAPTER 1 SNORKELING 23

26 THE SNORKEL VEST CHAPTER 1 SNORKELING The snorkel vest is basically a ring-shaped life buoy that can be inflated or deflated by the diver. Using the snorkel vest gives you greater comfort and safety: when inflated it enables you to swim more easily on the surface without getting tired; when deflated it allows you to make a surface dive to observe the fantastic underwater world from close up. PLACING YOUR SNORKELING EQUIPMENT So far we ve seen the gear that makes up your snorkeling equipment. Now you re ready to put it on and get in the water. We ll put on the equipment in a logical order, starting with the suit, then the boots, weight belt, snorkel vest, mask, gloves and finally the fins. It is important to remember that wherever you dive, the fins should be the last things you put on. Don t put them on until you re ready to enter the water because it makes walking uncomfortable and dangerous. If you must put your fins on sooner, we recommend you walk backwards. 24

27 ENTERING THE WATER How you enter the water depends on where you re diving and your own personal preferences. When you enter calm water from a beach, carry your fins until the water reaches your belt. Then, with the help of your buddy, put on your fins. If the sea is slightly rough, put your fins on immediately, then walk backwards until you reach water deep enough to swim and move quickly away from the shore. If you enter the water from the edge of a swimming pool or a low platform, sit on the edge with your legs dangling, push with your hands to one side and turn your body to enter the water. You can also enter the water from a low edge or from the swim platform of a boat, with a giant stride : stand with the blades of the fins protruding from the edge and take one big step forward, keeping your legs spread to slow down your sinking motion. From a platform or higher side of a boat, the best way of entering the water is with your legs together, following the same procedure as with the giant stride, but putting your fins together immediately so that your feet slice the water and reduce your impact with the surface. From a smaller craft you should enter the water with a backward roll: sit on the edge with your back to the water and let yourself roll backwards with your legs crossed. Remember that the best entry is always the easiest. Always enter with your vest partially inflated, your mask on your face and your snorkel in your mouth, ready to See, Breathe and Float. Beginning your dive properly, with a clean entry into the water, will help you to relax and enjoy every moment of the dive. CHAPTER 1 SNORKELING 25

28 CHAPTER 1 SNORKELING Checking your Weight The first thing you should do as soon as you have entered the water is to check that you are correctly weighted. With your body in a vertical position, the vest deflated and your lungs half empty, the water should come up to your eye level. When you breathe out completely, you should sink; then when you breathe in again, the water should reach chin level. Surface dives When snorkeling the desire to dive below the surface to have a closer look is irresistible! To do this you ll have to perform a surface dive. The traditional surface dive is head-first. Start by swimming slowly on the surface and then bend forward at the waist 90, pushing with your arms and then lifting and stretching your legs. At this point, your body is perpendicular to the surface and the weight of your legs pushes you downwards. When your fins are completely below the surface, all you have to do is kick to move deeper without splashing. It is very important to remember to equalize the pressure in your ears while starting your descent, before experiencing any discomfort. Simply pinch your nose with your fingers and blow gently. This pushes air into your Eustachian tubes and into the middle ear. This maneuver should be repeated as you continue the descent, whenever you feel water pressure on your eardrums. As soon as you have trouble equalizing the pressure, ascend immediately to avoid the risk of pain or injury and remember never to blow with excessive force. When you reach the surface after the dive you can empty the snorkel using the blow or expansion technique discussed previously. During the ascent, look towards the surface and hold your left arm up to avoid bumping your head into obstacles. Remember that diving is a sport best practiced in pairs. It is essential to always swim alongside your buddy and when one of the pair dives underwater, the other should remain on the surface to monitor his buddy. 26

29 EXITING THE WATER The best way of getting out of the water after the dive is to first remove your weight belt and rest it on the edge of the pool, or pass it to someone on the surface. Then exiting the water using a ladder, as you would on a boat or dock, remove your fins but keep your mask in place and snorkel in your mouth. If you re exiting onto a beach, remove your fins when the water reaches waist level, then walk out. If there are breaking waves present, swim in as far in as you can, then crawl out on your hands and knees. Only remove your fins when you are out of the water. SUMMARY This chapter has introduced you to the basic equipment you ll need to begin your discovery of the underwater world. Once you ve experienced these wonders, you will want to return again and again. Watch the SNSI OWD Snorkeling Skills Video CHAPTER 1 SNORKELING 27

30 STUDY GUIDE: CHAPTER 1 1. Which material are the mask lenses made of? 4. What kind of fins do you wear with diving boots? CHAPTER 1 SNORKELING Tempered glass. Plastic. Glass 2. Can you use swimming goggles to dive? Why? Yes. There is no difference between swimming goggles and a mask. No. They do not cover the nose. 3. Which side of the mask do you put the snorkel on? How? Right side. With a proper snorkel keeper. Left side. With a proper snorkel keeper. Either side. With a proper snorkel keeper. Open-heel fins. Full-foot fins. Either kind of fins can be used. 5. What is the best suit to wear with temperatures about 27 C /80 F? Lycra suit. Wet suit. Dry Suit. 6. The weight belt must be worn so that it can be removed with which hand? From left to right. With your right hand. From right to left. With your left hand. From the preferred side of the diver. 28

31 CHAPTER 2 SCUBA EQUIPMENT

32 CHAPTER 2 SCUBA 30

33 CHAPTER 2 INTRODUCTION Now that you have explored the underwater world from the surface, you will want to spend more time under the water. We will now learn to use the SCUBA unit, which enables you to stay under without returning continually to the surface to breathe. In addition to your snorkeling gear, SCUBA involves using some other equipment that we will discuss in this section. THE BUOYANCY COMPENSATOR DEVICE One of the most unique aspects of scuba diving is moving through the water like an astronaut through space. The equipment that enables you to do this is the BCD (Buoyancy Compensator Device), also called the BC (Buoyancy Compensator). By inflating or deflating it, you can control your position in the water through your buoyancy. You are negatively buoyant when you sink, positively buoyant when you float and neutrally buoyant when you neither sink not float, but remain comfortably suspended at your current depth. The BCD is usually a jacket-like configuration; some have a fabric outer layer and an internal inflatable bladder, while others have a single layer design. On your left shoulder you will locate one end of a corrugated hose that connects to the inner bladder. The other end contains an inflate/deflate mechanism connected to your tank by a low-pressure hose. By using buttons on the device, you can use the air from your tank to inflate or deflate the BC, or you can you can manually breathe air into the mouthpiece for inflation. Inside the corrugated hose a steel cable connects the inflate/deflate mechanism to a valve at the shoulder that will rapidly deflate the jacket when pulled. CHAPTER 2 SCUBA 31

34 CHAPTER 2 SCUBA In addition, some BCDs have a regulator that can be used as an alternative air source (backup regulator) attached to the end of the corrugated hose. Some newer-model BCDs don t have a corrugated hose but instead use an ergonomic handle on the body of the BCD. It contains buttons for inflation and deflation, activating twin purge valves that help deflate the BC regardless of the diver s position underwater. You can also orally inflate with a small rubber tube in the left pocket. A solid or flexible integrated panel, with a Velcro band and a buckle, attaches the BCD to the tank. You secure the BCD with a belt and series of BCD Buoyancy Compensator Device Adjustable Straps Inflate/deflate mechanism adjustable straps across your torso. If too much air is placed in the BCD, an over-expansion relief valve will Corrugated Hose automatically open and release the excess air. This valve may be either on your right shoulder or right hip; some BCDs may have both. BCDs have various characteristics that make them suitable for a wide variety of uses. You ll normally find pockets for holding diving accessories, and Velcro tabs used to secure the alternate air source and pressure gauge hoses. There are also BCDs with integrated weight pockets that replace a standard weight belt. They are equipped with a quick-release so that weights can be quickly released if necessary. It s important that you thoroughly understand your release system, and review its use with your buddy before diving. There are also BCs designed with their flotation on the back of the diver, also called butterfly jackets. These are used most commonly by technical divers, including cave divers, and divers using mixed gas mixes. 32

35 Choosing the BCD There are numerous models of BCDs to choose from. As mentioned previously, it can have a single layer made of an airtight fabric, or can consist of an inner bladder protected by an outer cover made of a strong, tear-resistant material. It is especially important that the BCD contains a sufficient quantity of air to keep two divers on the surface when fully inflated. It s also important to choose the correct size so that it and the tank stay in place without restricting movement or breathing. Using the BCD The buoyancy compensator has been instrumental in turning scuba diving from a macho activity into a recreational activity that everyone can enjoy. The BCD compensates for the loss of buoyancy due to the compression of your wet suit that takes place as you descend. To use your BC correctly, you deflate it to descend and then, as you swim deeper, you add small amounts of air to control your rate of descent. Once you ve reached your desired depth, you can inflate or deflate your BC until you are neutrally buoyant you neither descend nor ascend. Over-expansion relief Valve Integrated Weight Pockets You can then fine tune your buoyancy through your breathing. When you breathe in, your expanding chest increases your volume so you become slightly more buoyant; when you breathe out, you displace slightly less water, and your buoyancy will become slightly negative. To deflate the jacket, remember to lift the corrugated hose well above your head to release the air. To ascend, begin from a neutrally buoyant position and kick towards the surface. Release small amounts of air gradually to control the speed of your ascent, which must not exceed 9 meters/minute (30 feet/minute), or 20 seconds per 3 meters (10 feet). Once you have reached the surface, inflate the BC and relax; you should stay afloat without exerting any effort. THE CYLINDER The cylinder is the container in which you carry your air supply. Air is compressed inside the cylinder, which provides a considerable quantity of air, despite its small size. The cylinders are made of steel or CHAPTER 2 SCUBA 33

36 CHAPTER 2 SCUBA aluminum alloy and have a volume that ranges from 5 to 15 liters (30 ft 3 to 120 ft 3 ). It is important to remember that cubic feet refers to the volume of air that can be contained when compressed to a pressure of about 200 atm (3,000 psi), the liters indicate the volume contained in the cylinder at atmospheric pressure (1 atm = 14.7 psi). The cylinder has a valve that opens and closes the air outlet and allows the regulator to be attached. A cylinder with an attached valve is referred to in scuba diving as the tank. There are two types of valves: K valve and DIN. The regulator is attached to the K valve (or INT) by a Yoke (stem) with an O-ring seal; the DIN valve has a female thread that allows a regulator with a male thread and an O-ring seal assembly. The valve also includes a knob used to open Canadian Regulatory Authority Markings U.S. Regulatory Authority Markings TC 3ALM 207 Specification Code for Aluminum DOT 3AL 3000 Scuba Tank Markings bar Tank s service pressure psi and close the tank. The markings on the cylinder convey important information from the manufacturer and regulating agencies. They include the identification codes of the cylinder, the pressure to which the cylinder may be filled (working pressure), the test pressure, which is normally 1,500 psi (100 atm) higher than the working pressure and the date on which the cylinder was first hydrostatically tested. This test is conducted by filling the cylinder with water and then inserting compressed air at the test pressure; it is then inspected for signs of damage or fatigue to the metal. If the cylinder fails the hydrostatic test, it is discarded; if it passes it, the date is stamped on the tank. Testing requirements vary from country to country; U.S. Department of Transportation rules require hydrostatic testing of all scuba P LUXFER 03A02 S-80 Unique Serial Number Tank s Manufacturer Month and Year of Manufacturer Luxfer s model cylinder 34

37 DIN Valve K Valve (INT) tanks every five years. In Europe a new tanks can be used for 4 years before testing, then tested every 2 years. In addition to hydrostatic testing, all cylinders must be visually inspected once a year to make sure there are no internal impurities or rust inside. A sticker indicating the month and year of inspection is placed on the tank. It is a violation of US Federal law to fill the tank if the INT/DIN Adapter hydrostatic test date is over five years old. It is important to never store your tank when completely out of air to prevent possible contamination. THE REGULATOR When inflated, a truck tire s pressure is about 5 atm (75 psi). In comparison, a filled scuba tank s pressure can range from 200 atm (3,000 psi) to 230 atm (3,300 psi). It is obvious, therefore, that to breathe the air under water, you ll need to reduce this pressure. That s the function of the regulator; it reduces the pressure of the air to ambient pressure. This is accomplished by the two parts that make up the regulator - the first stage and the second stage. The first stage The first stage is the part of the regulator that attaches to the tank valve. It reduces the pressure of the air in the tank to an intermediate pressure of between 8 and 11 atm (120 psi and 160 psi), using a balanced pressure system. High-pressure air from the cyl- CHAPTER 2 SCUBA 35

38 CHAPTER 2 SCUBA Yoke First Stage (INT) Second Stage inder enters the first stage containing either a diaphragm or a hollow piston, depending on the regulator s design. On one side of the diaphragm or piston is the air flows toward the 2nd stage; on the other is a spring set to intermediate pressure. The spring keeps the air passage open until the pressure equals that of the spring plus the ambient pressure in the hose leading to the second stage. When this balance has been reached, the spring will compress and the airflow will stop. The second stage The second stage is made of a metal or other rigid, shock-resistant material. It s connected to the first stage by a hose and contains an elastic diaphragm that is in contact with the water, and a mouthpiece. When you inhale, a slight vacuum is created, bending the membrane inward. This activates a lever that opens a valve located just after the connection with the hose, allowing air to flow. When you exhale, the air exits the second stage through a one-way valve. You can also receive air manually by pressing a button on the second stage, which bends the diaphragm inward (purge button). THE ALTERNATE AIR SOURCE DIN First Stage In addition to your primary second stage, it s essential to have an addi- 36

39 tional air source for sharing air with a diver who has run out of air. By using an Alternate Air Source (AAS), two divers can breathe easily from the same tank. There are various types of AAS available and your choice depends on your personal needs and taste. The most widely used AAS is commonly know as an octopus, which is an additional second stage connected to the same first stage as the main regulator. Another type is integrated into the BC. It consists of a second stage connected to the end of the buoyancy compensator s low-pressure hose. You may even opt for two separate first stages, each with its own second stage; in this case you will have to use tanks with twin-attachment valves. There are also small second tanks available with their own regulator that can be used as Alternate Air Sources. Regardless of which type you choose, an AAS is a required piece of equipment. UNDERWATER INSTRUMENTS You will need a set of instruments that provide you with all the necessary information necessary for a safe and enjoyable dive. The submersible pressure gauge The submersible pressure gauge indicates the pressure of the air inside the tank. It connects by a hose to one of the high-pressure air outlets on the first stage, and consists of a numbered gauge that can measure pressures of up to 350 atm (5,000 psi). Most pressure gauges have the first 35/50 atm (500/700 psi) marked in red to indicate the minimum amount of air you should have at the beginning of your ascent. There are also pressure sensors that can transmit your air pressure wirelessly to a wrist computer. Using pressure, depth and your average breathing rate, the computer can calculate and provide an accurate reading of your remaining air supply. Alternate Air Source Pressure Gauges CHAPTER 2 SCUBA 37

40 CHAPTER 2 SCUBA The depth gauge The depth gauge indicates your current depth during a dive. It is basically a pressure measuring device displaying values from 1 to 60 meters ( feet). At each increase in pressure of 0.1 atm which corresponds to 1 meter ( 3 feet) of water (or 2.22 psi which corresponds to 5 feet), the needle moves one increment forward. These depth gauges may be analog or digital. Besides keeping track of your current depth to maintain your dive plan, you need to know the maximum depth reached during the dive. Analog depth gauges contain a maximum needle that moves with the needle indicating the current depth, and stays at the maximum depth reached during the dive. Digital depth gauges indicate the maximum depth on its display. Timing devices It s not only important to know how deep you ve dived, but to also be aware of how much time you ve spent under water. An underwater watch or a dive timer may be used for this purpose. Your underwater watch must have a counterclockwise bezel indicating each of the first 15 minutes, then indicating every 5 minutes through 1 hour. It should have an arrow or notch at 60 minutes, which also corresponds to hour 0. When you begin your dive, line up this 0 arrow with the minute hand. As the minute hand moves during your dive, you can easily view your elapsed dive time by seeing where it points on the bezel. It is important that the bezel can only be turned counterclockwise in case it s accidentally moved. This will display a longer rather than shorter dive than actually made, and errs on the side of safety when calculating your decompression status. The compass The compass is a useful device that helps you to check and maintain your direction. It helps you quickly locate your dive site, and provides the information need to return to your dive exit point. 38

41 You ll have additional opportunities to use your compass and have fun practicing the skill of underwater navigation in the SNSI Advanced Open Water Diver course. The underwater computer The underwater computer is an extremely useful instrument for recreational diving: it takes the place of your depth gauge and timing device. This reduces the instruments you need for the dive, and also provides additional information due to the device s data processing capabilities. Chapter four of this manual contains a full discussion on using computers. CHAPTER 2 SCUBA 39

42 CHAPTER 2 SCUBA USING THE SCUBA UNIT - SELF CONTAINED UNDERWATER BREATHING APPARATUS Now that you re familiar with the fundamental parts of your SCUBA equipment, you re ready to assemble it and have your first underwater experience. Assembling the equipment To assemble the SCUBA unit, place the tank in front of you with the air outlet facing away from you. Place the BC strap around the cylinder with the jacket facing forward, and buckle in place with the top edge of the jacket just a few inches below the valve. Check that the valve s or first DIN stage s rubber O-ring is in place and undamaged. Position your regulator so that the two second stages are on the right, and the pressure gauge and BC hose are on the left, then hand-tighten the first stage to the tank valve. With the tank closed, try inhaling from both second stages to check for leaks in the second stages. You should not be able to take a breath. Connect the low-pressure hose to your BC s hose. Position the pressure gauge so that the glass viewing port facing away from you. Then, press the purge valve of either second stage and open the tank valve slowly. When you hear air coming out of the regulator, release the 40

43 purge valve and continue to open the tank valve fully. You should now be able to breathe from both second stages. Check your air supply on the pressure gauge, then finally check your BC by inflating it until the over-expansion relief valve opens. To familiarize yourself with your buddy s gear, swap equipment and repeat the same checks. You re now ready to put on your gear and enter the water. DIN Valve K Valve (INT) Wearing your SCUBA equipment Use your dive buddy to assist you in donning your SCUBA unit. Before entering the water, do a final buddy check to see that the tank valves are open and your BCs are secure. To prevent damaging the environment by dragging unsecure gear through the water, be sure the AAS and submersible pressure gauge hoses are attached in some manner to your BC. As times, you may have a situation where you need to don your gear while in the water. To do this, inflate your BC and position the bottom of the tank towards you. Open the BC jacket, push down on the unit, then turn and sit on the BC. Place your arms inside the shoulder straps, allowing the BC to slide up your back, then fasten the belt. Entering the water with the SCUBA unit The same entrance techniques you learned for snorkeling can be used to enter the water wearing SCUBA. Keep in mind the increased weight of the gear, and be sure all hoses are fastened securely. Enter the water with your BCD partially inflated, your mask on your face and your regulator in your mouth in order to see, breathe and float. CHAPTER 2 SCUBA 41

44 CHAPTER 2 SCUBA The first descent To make your descent, remain in a vertical position with your head up and deflate your BCD completely. Breathe out completely and do not kick; you will begin to slowly descend. Remember to equalize the pressure in your ears immediately by pinching your nose and blowing gently, or by swallowing or moving your jaw. Breathing underwater Once you are familiar with your regulator, you will find it extremely easy to use. In the unlikely event that the regulator falls or is knocked from your mouth, you ll need to recover it and clear the water from it. You can do this easily by blowing into the regulator, which will push the water out through the exhaust ports. An alternate method is by simply pressing the purge valve, (the button on the front of the second stage) sending air from your tank to clear the water. You ll then be able to resume breathing normally from the regulator. There are two ways to recover your regulator. You can lean to the right and make a semicircle with your right arm. This should place the regulator hose over your arm so you can follow it down to your second 42

45 stage. You can also reach behind your head with your right hand and feel for the first stage then follow the hose to your regulator. Regardless of the method used remember to never hold your breath under water; always exhale a small stream of bubbles whenever the regulator is out of your mouth. Exiting the water Except for the additional weight of your equipment, exiting the water on SCUBA is similar to exiting with your snorkel gear. Some situations, however, such as diving from a smaller craft, requires that you take off the SCUBA unit in the water. To do this, first remove your weight belt and hand it up to someone in the boat. Do the same with your inflated BC, then climb on board. Dismantling the SCUBA unit When you have completed your dive, you ll need to dismantle your SCUBA unit. First, close the tank valve, then press the purge valve on one of the second stages of your regulators to release the pressurized air. You can then detach the low-pressure hose from the BC, and unscrew the first stage from the tank. Dry the protective cap of the first stage, then screw in place. Remove the BC and be sure place your tank in the rack, or place it in a horizontal position to prevent damage to it or to others. Once, disassembled, wash the BC and the AAS with fresh water dry before packing. CHAPTER 2 SCUBA 43

46 CHAPTER 2 SCUBA DIVING ACCESSORIES In addition to the your basic SCUBA equipment, there are many accessories that are extremely useful. Knife Your knife is an indispensable tool during the dive. You can use it to tap your tank and attract your buddy s attention, or to cut away entanglements such as discarded fishing line. It s most often worn on the inside of your calf, or in a compartment on the BC. Flags and floats It s important that boats are aware of any underwater activities so that divers can avoid a potentially serious or fatal injury from a collision. To alert boats of your presence, a special diver down flag is used to indicate divers in the water. The white and blue Alfa flag is the International Diver flag. A regionally recognized Diver flag is the red flag with a white stripe that can be flown from a boat or floating buoy to indicate the presence of divers. Regulations prohibit coming within a radius of 100 meters (300 feet) from the flag; the diver must remain within a 30 meters (100-foot) radius from the flag. In the United States, and destinations such as the Caribbean is frequented by North American divers, commonly use an alternate flag containing a red field with a white diagonal strip from corner to corner is used. In some regions, dive boats display both flags. Alfa Flag Diver Flag Surface marker buoy The surface marker buoy allows boats to locate divers making an ascent away from the anchor line or the ascent line of the boat. All divers should carry a Surface Marker Buoy (SMB); in some countries it is a legal requirement. During this course, a SMB with a 6-9 meters (20-30 feet) line wound on a grams (half pound) weight is sufficient. Stow your SMB in a BCD pocket so that it is easily accessible. 44

47 Surface Marker Buoy Whistle Air Pressure Signaling Device The whistle A whistle is used as a surface signaling device, and can be heard much further than just yelling. It can be very useful if you surface too distance from the boat. Attach the whistle to your BC so it s easily accessible. For underwater use, there are signaling devices that use air from your low-pressure hose to emit a loud sound to attract attention. Remember to use these devises only when absolutely needed; let others enjoy the silent underwater world. Underwater Lights As we descend, our vision begins to lose most of the colors of the spectrum. So, at depth, and most things appear blue. To restore color, you need to take a light source under water. Dive lights can be powered either by rechargeable or disposable batteries. Thermometer The thermometer can be a useful instrument when diving. Documenting water temperatures in your logbook can help you choose appropriate exposure protection when diving at a different site in the same region in the future. A thermometer is normally integrated into a dive computer, so there is no need to purchase one if you purchase a dive computer. Tool box and spare parts Let s imagine a scenario: you get up early in the morning, load your equipment into your car or boat, and travel miles to your dive site. Once you have arrived, you break your fin strap which causes you to miss the dive because you have no replacement. Or, you find your tank is missing an O-ring. CHAPTER 2 SCUBA 45

48 CHAPTER 2 SCUBA A simple spare parts kit will prevent ruining your entire day. It should include: -- Various O-rings; -- Mask strap; -- Fin straps and buckles; -- A one-piece scuba tool composed of various wrenches and screwdrivers; -- Small first-aid kit. The dive log The dive log is the diver s diary; if entries are consistently made, it provides proof of diving experience. The information recorded will come in handy when planning future dives. Gear bag To carry all the equipment we have discussed, you ll need a large gear bag. Your dive center will have a selection of bags specially designed for storing SCUBA gear, with gear-specific pockets and compartments. A mesh bag is especially useful when diving from a boat as it allows water to drain quickly. DIVELOG SNSI SCUBA NITROX SAFETY INTERNATIONAL q TRAINING DIVE q RECREATIONAL Course Instructor Instructor signature Dive site 1st dive Dive site 2nd dive Date Buddy Depth ABT RNT TBT Conditions PRE-DIVE CHECK: REPETITIVE DIVE PROFILE Group designation Surface interval Buddy signature q Equipment q Safety procedures Group designation ABT RNT TBT Group designation Suit Weight Cylinder psi Note: 46

49 CLEANING AND MAINTAINING THE SCUBA EQUIPMENT As we discussed previously, all gear, except for the tank and the weight belt, must be rinsed in fresh water to prevent salt corrosion. Be sure when you wash your regulator to have the protective cap securely placed on the first-stage air inlet to prevent water or dirt from entering. Take care not to depress the purge button on the second stage while rinsing so water cannot enter the hose and reach the first stage. A little water normally enters the BC while diving; to remove it, allow some fresh water to enter through the BC exhaust valve. Shake the jacket to distribute the fresh water throughout the inner bladder, then drain it and place the BCD in a cool, dry place to dry. Fill to half capacity with air to partially expand the bladder. If properly maintained, your equipment will continue to function for many years. Effective maintenance includes having equipment serviced by a professional at least yearly or as recommended by the manufacturer, and if necessary, repaired by a factory-qualified technician. SUMMARY Being familiar with all of your equipment is an important first step to becoming comfortable in the water. With practice, your confidence level will increase when using your scuba equipment, you will find that your dives become more relaxed and enjoyable. The sooner you purchase your own personal scuba gear, with the assistance and advice of your instructor and dive center, the sooner you will begin to experience our extraordinary oceans to the fullest. Watch the SNSI OWD Scuba Skills #1 Video CHAPTER 2 SCUBA 47

50 STUDY GUIDE: CHAPTER 2 1. How can you inflate your BCD? Orally inflating the BCD. 4. The underwater computer replaces: The depth gauge. CHAPTER 2 SCUBA With the air from the tank via the low-pressure hose. Both. 2. The first stage reduces the pressure of the gas from the tank to: An intermediate pressure. The ambient pressure. Does not reduce the pressure. 3. With the tank valve closed, try inhaling from the second stages, you should: Breathe easily. Can not breathe. Hard to breathe. The timing device. Both. 5. When should you begin to equalize? As soon as your head is underwater. As soon as you begin to feel pressure. Ears equalize themselves without any action. 6. All divers should carry a Surface Marker Buoy (SMB)? True. False. 48

51 Appendix to CHAPTER 2 DIVING USING A DRY SUIT

52 Appendix CHAPTER 2 DRY SUIT 50

53 Appendix to CHAPTER 2 INTRODUCTION At SNSI, we take pride in our forward-thinking approach to scuba diving. Beginning right at the basic level, we teach students how to dive with a dry suit. When diving in cold water (less than 21 C/70 F), wearing a dry suit will allow you to return from your dive feeling warm and comfortable. In this chapter, we ll discuss the advantages of diving using a dry suit, and the unique techniques used with this type of thermal protection. WHY USE A DRY SUIT In the past, cold water diving was practiced by only the most committed of divers willing to brave the elements wearing only wet suits. Dry suits were primarily used by commercial divers, and provided little freedom of movement or comfort. Today s dry suits are comfortable and easy to use, even for recreational divers, and have become commonplace in recreational diving. One reason for diving in cold water is the ability to observe the seasonal differences in the underwater environment. A dive site you may be familiar with in the summer will often be very different in winter. In winter you will experience different marine life and behavior than in the summer. Plus, the visibility is generally much better in winter (mainly due to the reduction in plankton). Because you can extend your bottom time, and make more dives before becoming uncomfortably Appendix CHAPTER 2 DRY SUIT 51

54 Appendix CHAPTER 2 DRY SUIT cold, a long weekend of winter diving can be a real joy. Another benefit to winter/cold water diving is, due to shorter daylight hours, you can optimize night diving activities. Night diving requires additional training, however, and will be explored in the SNSI Advanced Open Water Diver course. Although dry suits cost slightly more than most wet suits, a well-maintained dry suit can last a lifetime and, as we ve discussed, provide numerous benefits. In addition, eliminating the risk of hypothermia and may possibly decrease the risk of contracting decompression sickness (discussed later). Finally, keeping warm and dry during and after the dive also lowers energy consumption so you will be less tired at the end of a day of diving. TYPES OF DRY SUITS Trilaminate Dry Suit There are several types of Dry Suits available, so divers are able to easily choose which is best for their needs and type of diving. The primary difference between dry suits is the material used in their construction. For example the Trilaminate dry suit is made with sheets of butyl rubber alternated with sheets of nylon. This kind of suit can be custom fitted, is light, and can be easily repaired like the inner tube of a bicycle tire. However, because it is rather thin, it requires an effective undergarment to keep you warm. Closed Cell Neoprene Dry Suit Precompressed Neoprene Dry Suit 52

55 Vulcanized Rubber suits are made of the same material as inflatable boats. Heat and pressure are used to assemble the suit, which has virtually no seams. The repair method is the same as for the Tributil Laminate suit. Dry suits made of Closed Cell Neoprene are constructed in the same way as wet suits and are made of the same material. The collar and cuff are made of thin neoprene, and when folded back on itself to form a waterproof seal. Precompressed Neoprene dry suits are made with thicker neoprene that is compressed and coated with nylon. This makes them stronger without sacrificing elasticity and comfort. They are constructed by gluing and sewing neoprene, much like a wet suit. But unlike closed-cell neoprene, precompressed neoprene cells are permanently compressed and so the suit maintains its original characteristics. CHARACTERISTICS OF THE DRY SUIT Dry suits have various kinds of attached boots incorporated in their construction. They can have rigid soles, or can be a thinner sock-type boot that requires rigid-soled boots to worn over them to prevent tearing. Some dry suits are also equipped with knee-pads. Closure of the dry suit is realized through a dry (waterproof) zipper that allows the suit to be put on and removed with ease. Another component of the dry suit is the hood, which may be dry or wet. The wet hood is made of closed-cell neoprene, while the dry hood is made of latex and will keep your head completely dry, a great advantage when you dive in very cold waters. Wearing your dry suit The length of your dry suit is critical. You should Appendix CHAPTER 2 DRY SUIT 53

56 Appendix CHAPTER 2 DRY SUIT be able to stretch your arms fully upwards without encountering any resistance. It should not be too long, either, or your feet could come out of your boots when you re in the water. Many manufacturers offer custom-made suits for the best possible fit. Proper fit of the collar and cuffs is essential. Latex or Silicone collars and cuffs can be adapted by trimming until they fit without gripping too tightly. A neoprene collar and cuff can be stretched so your head and hands can fit through them. But if they re too loose, they should be replaced with a smaller size. Dry Suit Valves Dry suits have two valves; one for adding air and the other for expelling air. The inflate valves work much like the buoyancy compensator. They re normally situated at the center of your chest. When you press the valve button, low-pressure air from the scuba cylinder enters the suit. The low-pressure hose must be connected to prevent water from entering. Some models have a cap to close the valve for use in other water sports such as snorkeling. The exhaust valve of the dry suit is normally at the top of your left sleeve. There are two types: a manual release, activated by pressing the spring-loaded valve itself, or an automatic release that activates when the suit is over-pressurized. This valve is also loaded with a spring and can be adjusted to keep the air pressure (and volume) inside the suit constant. Because surplus air is expelled Silicone Collar Inflate Valve Boots Incorporated Dry Suit Exhaust Valve Silicone Cuff 54

57 from the shoulder area when you ascend to shallower depths, it s important to keep your body in a vertical position. You can fine-tune the expulsion of air simply by raising or lowering your arm slightly. These valves also have the option of manual control. The inflate valve generally lets in slightly less air than the exhaust valves can expel. This fail-safe design prevents uncontrolled ascents in the event that the inflating valve becomes stuck in the open position. There must always be an amount of air inside the suit to prevent it squeezing your body, but it is vitally important that the dry suit is never used in place of a buoyancy compensator. Inflate Valve. Press the valve button and low-pressure air enters the suit. Exhaust Valve. Press the button (manual release) or rotate the valve (automatic release) and vent the suit. Undergarment for Trilaminate Dry Suit Undergarment for Neoprene Dry Suit WHAT TO WEAR UNDER YOUR SUIT When diving in a dry suit, you ll normally wear an undergarment as well. There are numerous kinds of thermal undergarments available, each with various features. When buying your dry suit, your dive center professional will be able to advise you as to which undergarment is best for the suit you ve chosen and for the conditions in which you intend to dive. Appendix CHAPTER 2 DRY SUIT 55

58 Appendix CHAPTER 2 DRY SUIT DRY SUIT DIVING TECHNIQUES A dry suit is easier to put on than a wet suit, and can be comfortable to wear out of the water even in the rain or on chilly boat rides to the dive site. However, overheating is a risk when wearing a dry suit outside of the water in warm weather. It is usually best to prepare all of your equipment before putting your dry suit on. Once you have put on your undergarment, slip your legs into the suit first, then arms and finally place your head through the collar. Adjust your collar and cuffs: if the collar is made of neoprene, it must be folded back on itself, but there s no need to adjust a latex or silicone collar. Make sure that the collar adheres to your skin and that there is no hair or parts of your undergarments between the collar of your suit and your neck. The same should be done with your cuffs. To prevent water infiltration, be sure the zipper is completely closed; this is usually best performed with the aid of your buddy. Once your suit is on and zipped, expel the air inside it by bending at your knees and holding the exhaust valve open. You will enter the water with your dry suit the same way as you would with a wet suit. Once you re wearing the correct amount of weight (as determined in Chapter 1), you are ready to start your descent. First, you will need to release the air inside the dry suit as well as all of the air in the BC. By descending feet-first, increasing pressure will push the air inside your suit out through the exhaust valve. But just like equalizing the pressure in your ears and mask, you ll also need to 56

59 equalize the amount of air in your suit. Be sure there s enough air in your suit so that the fabric does not form folds, or cause a squeezing sensation. Your buoyancy is controlled using your BC. You ll need to expel the surplus air inside the suit as well as the surplus air inside the BC when returning to the surface. Keep your left hand on the exhaust valve of your BC when making your ascent. This position allows you to easily vent your BC, as well as automatically expel the air from the dry suit through the exhaust valve at the top of the left sleeve. Dry suit concerns Wearing a dry suit can make buoyancy control a bit more of a challenge. With your SNSI instructor s advice and a little practice, you will easily overcome any problems you may encounter. One unlikely possibility is the flooding of your dry suit. This is easily solved by removing your weight belt and inflating your BC. Another concern may be too much air in your suit due to an air inlet malfunction. If this occurs, quickly detach the low-pressure hose connected to the cylinder and expel the air from your suit. You may also find too much air in your suit when you change depth during a dive. If you ascend a few feet the air inside the suit will expand due to the decrease in ambient pressure, so it must be expelled. If for some reason your exhaust valve fails to release enough air, you can stretch the collar of the suit, releasing the excess air. Practicing using the dry suit The correct weight: Determining the correct amount of weight to use with your dry suit is similar to what you learned in Chapter 2, with some additions. With your dry suit on, expel as much air from it as pos- Appendix CHAPTER 2 DRY SUIT 57

60 Appendix CHAPTER 2 DRY SUIT sible by bending down and pressing the exhaust valve. When in the water, feet down with your BC deflated and holding a normal breath, the water should be at eye level. When you exhale, you should sink slowly. Collapse the dry suit: Descend underwater without inflating the suit until you feel a squeezing effect on your body. At this point you ll need to inflate your suit enough so the squeeze is eliminated. Once your suit feels comfortable, you should be able to practice controlling your buoyancy by inflating your BC orally and with the low-pressure valve. Check the flow rate of the valves: To prevent overpressurizing your dry suit, the flow rate of the exhaust valve should be higher than that of inlet valve. To check this, establish neutral buoyancy and adjust both valves of the suit at the same time to be sure the valves expel air more quickly than it inflates. Set the exhaust valve before starting the exercise and be ready to expel air from your collar or cuff if the buoyancy becomes excessively positive. Simulate an air inlet valve jam: In this exercise, your buddy continually presses your dry suit inflation valve. As soon as you feel positive buoyancy, detach the 58

61 low-pressure hose from your suit and immediately expel the excess air. Simulate the loss of buoyancy control: Achieve neutral buoyancy, then inflate your dry suit until you are positively buoyant. You can then practice expelling the excess air through the neck seal. This exercise will let a little water into the suit, but allows you to see how quickly and easily air can be expelled from the suit by moving the collar slightly away from your neck. Overturning: This situation can occur when the air inside the dry suit moves into your legs and boots, turning you upside down. To return to an upright position, bend your knees towards your chest and, with the aid of your arms, turn until you reach the correct position. Controlled ascent: To ascend in your dry suit, begin neutrally buoyant and kick slightly toward the surface. Expel air from both your BC and your suit to control the speed of your ascent. Stop at feet (4-5 meters) of depth, regain neutral buoyancy and simulate a safety stop. Once you re back at the surface, inflate your BC to achieve positive buoyancy. POST-DIVING PROCEDURES One of the rewards of diving with a dry suit is exiting the water feeling warm and dry. You ll also find it easier to remove your dry suit at the end of your dive. Start by removing the collar first; pull it away from your neck with two hands, lower your head forward and Appendix CHAPTER 2 DRY SUIT 59

62 Appendix CHAPTER 2 DRY SUIT pull the collar from the back of your neck to the top of your head. To remove the cuff, stretch it gently and slide your hand inside. CLEANING AND MAINTAINING THE DRY SUIT Regular maintenance and care of the dry suit will prolong its life and protect your investment in your gear. After every dive your dry suit, like the rest of your equipment, must be rinsed with fresh water and air dried. Avoid getting water inside and give particular attention to the valves, collar and cuffs, especially if they are made of latex or silicone. The zipper must be lubricated frequently with wax to prevent the material from forming rust and malfunctioning. The inside of the suit does not have to be rinsed unless seawater has penetrated it. Once rinsed, place your dry suit in a cool, dry place, away from direct sunlight to prevent fading and deterioration of the fabric. If the suit is not to be used in the near future, it should be kept in its bag, protecting any latex cuffs or collars with talcum powder. If torn, the suit can be repaired by your dive center s trained personnel. 60

63 SUMMARY Over the past few years, the use of dry suits in recreational diving has spread dramatically. For this reason, SNSI has included this equipment in its Open Water Diver training so you can begin using it as soon as your second dive in a swimming pool or confined water. We are confident that the using a dry suit as a recreational diver will allow you an even greater appreciation of your new activity! OPTIONAL: If You used Dry Suit during all the in-water sessions, You will have qualified to be certified as a SNSI Open Water Dry Suit Diver. X Appendix CHAPTER 2 DRY SUIT 61

64 STUDY GUIDE: Appendix to CHAPTER 2 Appendix CHAPTER 2 DRY SUIT 1. How can you inflate your Dry Suit? Orally. With the air from the tank via the low-pressure hose. Both. 2. Where is the deflate valve normally found on the dry suit? At the top of the left sleeve. At the top of the right sleeve. At the top of the left leg. 3. Can you use the dry suit in place of the BCD for buoyancy control? Yes. No. Sometimes. 62

65 CHAPTER 3 THE PHYSICS OF DIVING

66 CHAPTER 3 THE PHYSICS is certified by: ISO : SNSI Scuba Diver. ISO : SNSI Open Water Diver. ISO : SNSI Divemaster. ISO : SNSI Confined Water Instructor. ISO : SNSI Open Water Instructor. ISO 11121: SNSI Experience Scuba ISO 11107: SNSI Recreational Nitrox Diver ISO 13293: SNSI Gas Blender is RSTC Member 64 SCUBA AND NITROX SAFETY INTERNATIONAL

67 CHAPTER 3 INTRODUCTION The natural environment for humans is, of course, on the earth s surface. When you dive, however, you enter a very different environment. Even though you will have specialized equipment to help you adapt to these changes, you also need to be aware of how various physical laws affect your body while under water. Breathing under water is obviously a primary concern. Besides using the equipment we have discussed, it s also important that we understand how pressure at depth affects our breathing. This chapter will explain both: proper breathing techniques while scuba diving and also how to maintain neutral buoyancy and make safe and comfortable descents and ascents. BREATHING AND GAS EXCHANGE Breathing starts with nerve impulses going from the brain to the intercostal muscles that surround our ribs. As these muscles contract, they lift the ribs and, at the same time, lower the diaphragm in the abdominal cavity. As a result of these muscle movements, a partial vacuum forms and air flows into the expanding lungs. The lungs are like spongy bags ending in tiny air sacks called alveoli, which are surrounded by equally tiny capillaries. With each breath, air flows through the respiratory tract (nose, mouth, pharynx, larynx, trachea and bronchi) and into the lungs. At sea level, air contains approximately 21% oxygen and 79% nitrogen, as well as small amounts of other gases. When you breathe in, oxygen is absorbed CHAPTER 3 THE PHYSICS 65

68 CHAPTER 3 THE PHYSICS Trachea Bronchi Air inhaled O 2 Rib cage expands Diaphragm contracts (moves down) Inhalation Diaphragm Lungs Alveoli Air exhaled CO 2 Diaphragm relaxes (moves up) Exhalation Rib cage gets smaller into the blood through the thin walls of the alveoli in the lungs. Once filled with oxygen, blood returns to the heart and is pumped through the arteries throughout the body. In the same way that oxygen is absorbed by the blood, carbon dioxide is transferred from the cells to the blood as a waste product. Veins return it to the lungs where it passes through the alveoli and is exhaled. Nitrogen, an inert gas, does not participate in this exchange of gases. The stimulus to breathe is determined by the level of carbon dioxide in the blood. When the level rises, the brain sends signals via the central nervous system to the breathing muscles, increasing the frequency of breathing cycles. With just slight differences, breathing underwater is the same as on land. We usually maintain our regular breathing rate, but tend to breathe more deeply due to the increased pressure/density of the air delivered by the regulator. Increased physical effort, such as when swimming against a strong current, can cause us to breathe faster and shallower. This breathing pattern does not allow us to eliminate sufficient carbon dioxide, and the increased level causes us to breathe even faster. The solution is to stop, concentrate and force yourself to breathe more deeply until your rate returns to normal. Proper breathing consists of inhalation and exhalation with no pauses. The most important thing to remember is to never hold your breath. Even if the regulator is out of your mouth, you must continue to exhale a small stream 66

69 of bubbles. It is also important to keep your regulator in proper working order to prevent any breathing difficulties. Pulmonary Arteries Oxygen Poor CO 2 Rich Blood Circulatory System Lungs Heart Body Pulmonary Veins Oxygen Rich CO 2 Poor Blood Capillary bed of all body tissues where gas exchange occurs FIRST AID FOR BREATHING CEISURES When breathing stops, the gas exchange process is interrupted and suffocation or asphyxia takes place. When this happens in the water, it may result in drowning. Somebody who stops breathing must receive artificial respiration. Even in a non-breathing individual, the heart continues to pump blood for a few minutes, so immediate restoration of breathing may prevent the stopping of the heart. If the heart does stop, then cardiopulmonary resuscitation (CPR) will be necessary. CPR may only be administered by those who have been trained in the procedure; it is therefore advisable that divers complete the SNSI BLS First Aid course. If you see a person on the surface with no signs of life, first determine if they are conscious; if not, make sure they can float. If they are wearing scuba gear, release their weights. You can then open the airway by putting your hand on the forehead and pushing up on the back of the neck with your other hand. Listen closely for any CHAPTER 3 THE PHYSICS 67

70 CHAPTER 3 THE PHYSICS sign of breathing; if not, call for help and begin mouth to mouth resuscitation. Take off your mask; if the victim is wearing a mask, leave it on. If not, pinch his nose closed and blow two quick breaths into his mouth. Begin moving toward the boat or shore while administering a breath every 5 seconds. Once ashore or onboard the boat, cardiopulmonary resuscitation must begin. CPR requires 30 chest compressions, then two breaths into the victim. Specialized training is required to perform a rescue, it s therefore advisable that divers complete the SNSI Rescue Diver course. The previous section on breathing demonstrated the importance of having healthy lungs. Even otherwise healthy divers may have difficulties caused by acute or chronic pulmonary problems. Any cause of breathing obstruction, such as the flu, a cold, or chronic sinusitis may create problems for divers. Of even greater concern is diving with asthma. For those affected, it is important that these conditions are assessed by a physician who is familiar with diving medwww.scubasnsi.com PHYSICAL CONDITION AND DIVING Due to modern equipment, recreational diving does not require exceptional strength or stamina. But because your body is subjected to changes in pressure and some degree of physical effort, you should be in reasonably good physical condition; specially your cardiorespiratory system. 68

71 icine before you begin any training. We are all familiar with what we need to do in order to maintain a good physical condition: get adequate rest, eat a balanced diet, and exercise regularly. Periodic check-ups are also important, especially if you re over 45 years old, if you take medications regularly, if you have recently had surgery or if you have cardiac or respiratory maladies. There are also a few considerations that should be made for women learning to dive: While fewer than 10% of diving students were women 20 years ago, today about 30% of certified divers are women and the number is increasing continually. There are obviously physiological differences between men and women; differences in muscle development, distribution of body fat, weight and size of the lungs. But, the differences due to sex are far less important than those due to differences in physical condition, cardiovascular efficiency, age, weight, ease of movement and underwater capabilities. One concern for women is diving during the menstrual period and pregnancy. As a general rule, if you re capable of performing physical activities on land, you should have no concerns while diving. If menstrual pains and muscle spasms are strong, underwater activities may be contraindicated. With regard to pregnancy, however, the effects of water pressure on the fetus are not well known, so diving activities should be suspended if you are, or suspect you may be, pregnant. But regardless of gender every diver should strive to maintain a reasonable level physical condition in order to dive safely and comfortably. CHAPTER 3 THE PHYSICS 69

72 CHAPTER 3 THE PHYSICS ADAPTING TO THE UNDERWATER ENVIRONMENT Matter is made up of groups of atoms called molecules, and exists in three states: solid, liquid and gas. At relatively low temperatures, molecules form regular crystalline structures and the matter is generally solid. Though always in motion, the molecules move in fixed positions. When the temperature rises, the molecules move further apart, slipping and sliding past one another, and matter becomes liquid. At an even higher temperature, the molecules move even more quickly and further away forming a gaseous state. Most of our body s tissues are comprised mainly of water and liquids and, for our purposes, are uncompressible. But gases, due to the large distances between their molecules, are highly compressible. Although the concept of air being a substance was considered even by the ancient Greeks, it was not until Galileo s time that Evangelista Torricelli demonstrated that the earth s atmosphere at sea level exerts enough pressure to push 760 mm (29.92 inches) of mercury (Hg) up into an empty glass tube. Furthermore, a French philosopher and scientist, Blaise Pascal, demonstrated that the weight of the atmosphere was equal to the pressure exerted by 10 meters (33 feet) of seawater. We live at the bottom of an ocean of air that is influenced by the force of gravity and is therefore compressed against the earth s surface. This ocean of air is called the atmo- 70

73 sphere and extends upwards for tens of kilometers (or miles) and exerts pressure on and in our bodies, even though we don t feel it. This pressure is referred to as atmospheric pressure and is equal to the weight of a one centimeter-square column of air that stretches from the surface of the earth to the edge of the atmosphere. The pressure equals about 1 kg/cm 2 (or 14.7 lbs. per square inch, commonly indicated as 14.7 psi - pounds per square inch) or 1 atm. As mentioned previously, 10 meters (33 feet) of seawater exert the same pressure as the entire atmosphere. So, we can see that the hydrostatic (water) pressure increases by 1 atm (14.7 psi) every 10 meters (33 feet) of depth. At a depth of 10 meters (33 feet), the pressure equals the sum of 1 atm the atmospheric pressure of 1 atm (14.7 psi) plus the hydrostatic pressure of 1 atm 1.01 bar (14.7 psi). The diver is therefore subjected to an ambient (surrounding) pressure, 101,325 Pa also called absolute pressure, of 2 ata (atmospheres absolute) or 29.4 psia (pounds 1.03 Kg/cm mmhg per square inches absolute) or. Although there is a small difference between atm inhg and bar, for our purposes we will consider 1 atm equal to psi bar. We have all experienced the effects of increasing pressure when we swim under water, such as the increasing pressure in our ears when diving to the bottom of a swimming pool. As divers we need to become familiar with the effects of pressure not just on our ears, but on the rest of our body, and how to deal with it. The English scientist Robert Boyle, continuing Torricelli s work, discovered that as pressure increases or decreases, the behavior of a gas is extremely predictable. His findings, known as Boyle s law, state that, at a constant temperature, if pressure is increased in a container, the volume of the gas decreases. The exact opposite is also true when the pressure is reduced. Further studies by Daniel Bernoulli explained the mechanism of Boyle s law as the effect of collisions between the molecules and the walls of the container: the more quickly the gas molecules move, the higher the number of collisions. Bernoulli concluded that when the density of a gas increases, the number of collisions also increases. An increase in the number and impact of the collisions causes the pressure to rise. CHAPTER 3 THE PHYSICS 71

74 CHAPTER 3 THE PHYSICS Note that temperature is also a consideration in Boyle s law. Scientists Charles and Gay-Lussac observed that when the temperature of a gas in a container, such as a scuba tank, is increased, the pressure inside the container increases. So, when the gas volume is constant, the temperature and pressure are directly proportional. This explains why, when tanks are filled, they warm up. They will also indicate a higher pressure just after the refill than when they have cooled down. This increase in pressure is the reason your tank should not be left in the direct sunlight when full. Cold Hot Effects of Charles and Gay-Lussac s Law: When the temperature of a gas in a scuba tank is increased, the pressure inside increases. Sea Level 1 ata (14.7 psia) Gas Volume 1-10 m (- 33 Feet) 2 ata (29.4 psia) Gas Volume ½ -20 m (- 66 Feet) 3 ata (54.1 psia) Gas Volume ⅓ EFFECTS OF THE INCREASE IN PRESSURE Based on what we have learned so far, we can easily calculate the ambient pressure (absolute) at the various depths during your dives. At 10 meters (33 feet) of seawater, the pressure is double that on the surface, i.e., 2 ata (29.4 psia), at 20 meters (66 feet) three times, or 3 ata (44.1 psia), and at 30 meters (99 feet) four times, or 4 ata (58.8 psia). Similarly, the volume of a gas in a flexible container will decrease in proportion to the depth (pressure). For example, at 10 meters (33 feet) of seawater the receptacle will have half the volume it had on the surface. At 20 meters (66 feet) it will have a third, at 30 meters (99 feet) a quarter and so on. What is the effect of this pressure on you? Being primarily fluid, our tissues are mostly unaffected by changes in pressure. However, our air-filled spaces are very much affected; and the consequences of the changing pressures on ascent and descent are sometimes referred to as direct effects (we ll learn about indirect effects later). The air cavities of our body are the: lungs, respiratory tract, cranial sinuses, gastrointestinal tract and the middle ear. These struc- 72

75 tures do not have stiff walls and can expand and contract, requiring that we equalize any pressure exerted on them. Equalizing pressure means keeping the pressure of a gas contained in a receptacle equal to that of the external environment. The pressure may be equalized in the following two ways: -- By changing the volume. If external pressure increases on a hollow organ, causing the volume to decrease, the pressure of the gas inside the organ will increase in proportion and the internal pressure and external pressure will be equal. -- By inserting gas into the organ to equalize the pressure. If you insert an adequate amount of gas into the organ as the external pressure increases, the internal pressure will remain balanced with the external pressure and the volume of the organ will not change. Both of these methods of equalizing pressure are used in diving. The abdomen and intestines are equalized through a decrease in volume while the respiratory tract and lungs are balanced by breathing the ambient pressure air supplied by your regulator. However, we need to address equalizing pressure in your ears, sinuses and some parts of your equipment in more detail below. EQUALIZING PRESSURE The ear The ear is a complex organ designed for two important functions: hearing and balance. It s divided into three sections: external, middle and internal ear. The external ear is made up of the pinna and the ear duct as far as the eardrum (tympanum) where the middle ear begins. It transmits the vibrations produced by sounds on the eardrum to the inner ear. The middle ear is a small cavity containing air, and is connected to the respiratory tract (pharynx) through the Eustachian tube. This tube is normally closed, so the middle ear is essentially a CHAPTER 3 THE PHYSICS 73

76 CHAPTER 3 THE PHYSICS External Auditory Canal Tympanic Membrane Middle Ear Internal Auditory Canal Cochlea Eustachian Tube closed container that is exposed to external pressure by the flexible wall of the eardrum. If external pressure increases, the eardrum may be forced inward, decreasing the volume of the middle ear. To equalize this pressure, we must open the Eustachian tube and insert air into the middle ear by means of the Valsalva maneuver. To perform this maneuver, pinch your nostrils with your fingers, then blow gently but firmly into your nose. This procedure should not be done with excessive force. For most divers, the Valsalva maneuver is necessary to equalize the pressure in your ears; however you may be able to equalize the pressure simply by moving your lower jaw forward (or back and forth) or by swallowing. Regardless of how it is accomplished, it s important that you begin equalizing immediately, on the surface before starting your descent. If the pressure inside your ear is equalized correctly, you should feel no discomfort. If you do, ascend slightly and repeat the maneuver. The sinuses The sinuses are cavities present in the skull. They are connected to the nose and throat by a network of passages. Normally, the airways inside sinuses are open and are equalized when the ears are equalized. But sometimes, equalization of the sinuses is difficult due to obstruction of one or more tubes due The sinuses to swelling and congestion caused by a cold, allergies, infections or other chronic disorders. This may cause pain on the forehead, cheekbone or upper teeth. If this occurs, it is best to postpone the dive until the condition has been resolved. The equipment As described in chapter one, the piece of equipment that requires pressurization is your mask. Failure to equalize the air pressure inside the mask may cause a sensation of excessive pressure on your face during your descent. When you return to the surface, your eyes may be red and bloodshot: this is referred to as a squeeze. It is very easy to prevent: simply exhale a little air through your nose during your descent. This equalizes the pressure inside the mask with the ambient pressure. 74

77 The symptoms from a squeeze disappear spontaneously. However, if you display signs, suspend diving until they have disappeared. EFFECTS OF DECREASING PRESSURE During your ascent, the reduction in water pressure causes an increase in the volume of the air inside the body cavities and the equipment (Boyle s law). This concept is easy to understand but is vitally important to your safety as a diver. Although very few divers will ever encounter this problem, gas expansion may cause serious injuries, so you must be aware of the causes and treatment of various conditions known collectively as lung overexpansion injuries. In normal diving situations, divers return to the surface inhaling and exhaling normally. Any expanding air in the lungs produced by the reduction of pressure on ascent is eliminated. However, holding your breath on an ascent prevents AGE Arterial Gas Embolism Mediastinal Emphysema expanding air from escaping, and can cause serious, life-threatening injury. The injury is caused when the lung expands beyond its capacity. In this case, air from the alveoli can enter the circulatory system in the form of bubbles. The bubbles can then block blood flow in any part of the body, including the brain. This is referred to as a pulmonary embolism. Symptoms of an embolism range from mild, such as sluggish limbs; to severe, including temporary loss of vision, speech or hearing, paralysis, loss of consciousness or death. If air escaping from the lung moves into the space between the lungs (mediastinum), heart and trachea, the result is called a mediastinal emphysema. Subcutaneous Emphysema This condition exhibits symptoms of chest pain, breathing difficulty and weakness. This escaping air can also collect below the skin around your neck and upper chest. This is referred to as subcutaneous emphysema, a visible swelling at the base of the neck that may cause breathing and speaking difficulties. Pneumothorax CHAPTER 3 THE PHYSICS 75

78 CHAPTER 3 THE PHYSICS Failure to vent excess air on ascent can also cause the extremely thin layer of tissue (pleura) that covers the surface of the lungs to break. This allows air to enter the chest cavity and the collapse the lung, a condition known as a pneumothorax. The symptoms of an overexpansion injury usually appear immediately or within 15 minutes of surfacing. Depending on the severity of the injury, there may be breathing difficulty, coughing or bloody sputum. Regardless of the severity, the diver must be taken to a medical facility. It is important that the injured diver be placed immediately on oxygen at a 100% concentration (or as close as possible). This will help oxygenate any tissues compromised by reduced circulation caused by the injury and help rid tissues of any air pockets that may have formed. All victims of pulmonary overexpansion will require immediate medical attention and may require treatment in a recompression chamber. The most frequent cause of lung expansion injuries is a rapid ascent when a diver runs out of air due to poor planning or inattentiveness. We will discuss how to handle - and prevent - outof-air emergencies later in this chapter. The good news is that prevention of all of these conditions is simple: Never hold your breath while diving; breathe continuously. 76

79 THE HUMAN BODY UNDERWATER Overheating and hypothermia Our bodies function most efficiently within a narrow temperature range. Depending on circumstances such as exercising under water, or just being immersed in water, body temperature may rise (hyperthermia), or decrease (hypothermia) dangerously. In terms of hypothermia, it may not seem obvious, but body heat is lost every time we exhale. When our body temperature drops from the normal 98.6 F (37 C) to 95 F (35 C), problems arise. If the loss continues, and body temperature drops to 90 F (32 C), we begin to lose the ability to reason, and at temperatures below 90 F (32 C), life is at risk. So, in order to dive both comfortably and safely, we need to be able to keep our body temperature stable. When we re immersed in water, our body s initial response to heat loss is to restrict the flow of blood to our limbs in order to protect the vital organs in our core. If we stay in the water for a longer time, this response is not sufficient to keep our core temperature stable and the body attempt to produce heat by shivering. When immersed, shivering cannot generate enough heat to restore a sufficient body temperature. Therefore, if you begin to shiver, take it as a sign that you have become too cold and end your dive. Exit the water immediately, put on warm, dry clothing, stay in the sun and drink hot, non-alcoholic drinks. CHAPTER 3 THE PHYSICS 77

80 CHAPTER 3 THE PHYSICS The best defense against hypothermia is wearing a dive suit that s the proper thickness, and that fits well. Proper insulation is especially important around areas of greatest heat loss such as the head, neck, groin and armpits. Although cold is often a factor in diving, so too is the need to avoid overheating (hyperthermia). For divers, hyperthermia may be most often caused by wearing a dive suit for too long before or after a dive. The first symptom of hyperthermia is increased sweating, as your body attempts to lower its temperature by evaporation. Of course, sweat cannot evaporate if you are covered by an exposure suit, so there s no way your body can cool off. To avoid overheating, don t put on your suit too soon before diving, especially if you ll be in direct sun. You can also cool off by pouring cool water into your wet suit, or by briefly entering the water if you re wearing either a wet or dry suit. Seeing underwater Our eyes are suited to life on the surface, so to see under water we need to make some adjustments. As you learned in the previous chapter, to see clearly underwater you need a mask to provide an air pocket in front of your eyes. But even with your mask, your vision in the water is slightly distorted due to the bending (refraction) of light. The rays of light entering the water are bent, which makes objects look about 25% closer and 33% larger. So actually, objects are further away and smaller than they look. Light rays are not only refracted when they enter the water, but they are also absorbed. This means there is less light as we descend. We also lose color as we descend, beginning with reds and oranges. The rest of the spectrum also fades away until everything appears blue and grey. Without Underwater Light Image 25% closer 33% larger Real Image With Underwater Light 78

81 Ascent Descent Here Cold Boat Go Back Help Look at Me Level Off Here Equalizing Problem Stop Share Air Come Here Something is Wrong OK OK on Surface OK on Surface Which Direction? (One Hand) Low on Air Out of Air CHAPTER 3 THE PHYSICS 79

82 CHAPTER 3 THE PHYSICS To solve this problem, just take an underwater light along on your dive to restore natural colors. Sound On land, we determine the origin of a sound by the tiny difference in time between the wave striking one ear, and then the other. However, sound waves move through water about four times faster than in air, due to water s increased density. This higher speed makes it very difficult to establish the direction from which a sound is coming. This makes it more difficult to attract the attention of another diver, or to determine the location of boat noise. Since we can not talk under water, we can communicate by means of a system of hand signals developed specifically for diving, or with underwater slates. There are even more sophisticated electronic full-face mask communication systems that we will address in a specialty course. MAKING YOUR ASCENT At the end of each dive, you will obviously need to return to the surface. As you have read previously, it s important that you make your ascent properly to avoid potential injuries. Normal ascent Before ascending, take a moment to stop and verify that both you and your buddy are ready to end your dive. Begin your ascent by first locating the exhaust valve on your buoyancy compensator and holding it in your left hand, reaching above your head. (The alternate technique is to locate the BC s dump-valve lanyard.) Begin your ascent neutrally buoyant, kicking slowly toward the surface, keeping an eye on your instruments so your speed does not exceed 30 feet (9 meters) a minute. Since air expands on ascent, you will probably need to delete excess air from your BC to maintain a proper ascent rate. Look at your buddy while keeping an eye on what s above your head, making sure there are no obstacles. Continue breathing normally. Once you have reached the surface, inflate your buoyancy compensator with a comfortable amount of air and you can float 80

83 effortlessly. Once at the surface breathing from your snorkel may be easier than using your regulator. Using the Surface Marker Buoy A situation may arise where you are not able to locate the boat or ascent line. In this case a surface marker buoy (SMB) may be useful. To launch an SMB start with slight negative buoyancy (this will be offset by the air filling the device). Be sure that you are at a depth at least 3/5 meters (10/15 feet) less than the length of your line or it cannot reach the surface. Once the SMB is deployed, keep the line taut so that the SMB remains upright on the surface, enabling the boat to see your location. If you let the line go slack, the SMB will not remain upright and may deflate. A responsible diver must be proficient in launching an SBM because factors such as poor visibility or poor navigation skills make losing track of your boat or ascent line location a common occurrence. And ascending without the aid of an anchor, ascent or SMB line will make maintaining your position while making a safety stop in shallow water difficult. The device may also be critical in helping the boat locate your position. Emergency ascents In Chapter Two, we discussed the importance of regularly checking your underwater instruments. Without periodic referral to your submersible pressure gauge, you could run out of air while still at depth. If this happens, there are several procedures for making a safe ascent, depending on circumstance. Alternate air source ascent By using the buddy system, an out-of-air problem can be solved with ease. If one of you runs out of air, the other can simply supply air using an alternate air source, or AAS. To perform this ascent, the out-of-air diver must signal the buddy and make the situation known. Depending on the type of alternate air source used, the donor can pass the recipient the primary regulator (one that s in use), then locate and use the alternate air source. Be aware that AAS devices can differ considerably. It can be a spare second stage (often with a longer than normal hose for ease of use by the buddy). This configuration is often called an octopus. CHAPTER 3 THE PHYSICS 81

84 CHAPTER 3 THE PHYSICS Another common configuration is an AAS built into the BC inflator system. In this case, the device serves a dual role as an inflator and emergency regulator. As systems can vary, it is important to familiarize yourself with your buddy s equipment prior to the dive. When you are low or out of air there is no time to learn how your buddy s system works! When sharing air, it is essential for buddies to remain in close contact: hold onto your buddy s BC or forearm with your right hand, maintaining a firm grip. This leaves your left hand free to control your buoyancy compensator inflate/deflate button. Once you have established contact and positioned the AAS so that both divers can breathe easily, make a normal ascent. Remember, once on the surface, the out-of-air diver must orally inflate his BC to establish buoyancy, because there is no air left in his tank. If further buoyancy is needed, release your weight system. Air Sharing Ascent Another ascent option made with buddy s assistance is to share the same air source. This is called buddy breathing, and may be the only option if your buddy does not have an AAS. The technique involves passing a single second stage between divers, and taking turns breathing from it. While this is not the best option, as it is more complex and stressful than using an AAS, it may be an option in an emergency. However, it does require practice to maintain proficiency at the skill. 82

85 Here, as the regulator is passed alternately from the donor to the recipient, each takes two breaths, exhaling first to clear the water in the second stage. Remember, when the regulator is out of your mouth, you must exhale by blowing a small stream of bubbles from your mouth to avoid the potential for a lung expansion injury. The recipient diver maintains contact, holding his buddy s BC shoulder strap firmly with his right hand. Do not rush, but remain at depth until both divers are comfortable with the technique. Then, ascend slowly following the same procedure as in the AAS ascent. Emergency swimming ascent The emergency swimming ascent is used when there is no buddy to supply air. Begin by keeping your regulator in your mouth and kicking toward the surface. To prevent injury from the expansion of air CHAPTER 3 THE PHYSICS 83

86 CHAPTER 3 THE PHYSICS in your lungs on ascent, you must exhale slowly and continuously throughout the ascent. To maintain a constant (neutral) lung volume not too much or too little many find making a continuous sound useful. The regulator is retained because, if you have an urge to inhale, it s best to do so with the device in place rather than risk inhaling water. Additionally, depending on your depth, the reduction of ambient pressure on ascent may allow you to get a breath or two from the tank as you ascend. You should be prepared to release air from your BC as it will expand during the ascent, making it difficult to control your speed. On the other hand, be prepared to release your weights in case you cannot ascend fast enough. Emergency Buoyant Ascent The emergency positive buoyant ascent is made when the diver runs out of air unexpectedly and is not confident in reaching the surface. In this case, weights are released providing immediate positive buoyancy. It is vital as in the swimming ascent to exhale continually to expel expanding air from the lungs. As you ascend, look up towards the surface, and be prepared to release some air from the BC to establish some control of your ascent rate. You can also slow your ascent, once you are close to the surface, by spreading out your arms and legs, and arching your back to create resistance. How to breathe from a Free Flowing Regulator Modern regulators are designed so that a malfunc- 84

87 tion creates a continual supply of air rather than an air termination. This is called a free flow. Although you never begin your dive with a free-flowing regulator, the problem may occur during the dive. It can almost always be traced to a failure to maintain your regulator, so have it serviced annually. If your regulator begins to free flow at depth, hold the mouthpiece gently in your mouth. This allows the excessive airflow to escape and avoid potential lung damage. An alternate technique is removing the regulator from your mouth and holding it against your lips, sipping or taking in just the amount of air you need while letting the excess air flow freely into the water. Once you have reached the surface, close the tank valve to prevent draining the tank of air. SUMMARY Even though the subjects discussed in this chapter deal with accidents and emergency procedures, it is important to know that they re rarely encountered or needed. If divers remember the few rules that we have discussed, stay in good physical condition, observe the buddy system and check their equipment regularly, accidents rarely occur. Watch the SNSI OWD Scuba Skills #2 Video CHAPTER 3 THE PHYSICS 85

88 STUDY GUIDE: CHAPTER 3 CHAPTER 3 THE PHYSICS 1. The stimulus to breathe is determined by: The level of carbon dioxide in the air. The level of carbon dioxide in the blood. The level of nitrogen in the blood. 2. The weight of the atmosphere is equal to the pressure exerted by: 10 meters / 33 feet of seawater. 1 meter / 3.3 feet of seawater. 20 meters / 66 feet of seawater. 3. At a constant temperature, if pressure is increased in a container, the volume of the gas... O O... remains the same. O O... increases. O O... decreases. 4. When the temperature of a gas in a container is increased, the pressure will... O O... increase. O O... remain the same. O O... decrease. 5. At 66 feet / 20 meters of seawater the volume of a gas in a flexible container will: 1/3 on the surface. The same on the surface. 1/2 on the surface. 6. How do you equalize your mask? Exhaling a little air through your nose. Exhaling a little air through your mouth. Both. 86

89 CHAPTER 4 THE PHYSIOLOGY OF DIVING

90 CHAPTER 4 PHYSIOLOGY SCUBA AND NITROX SAFETY INTERNATIONAL We take You ADVANCED OPEN WATER DIVER Deeper feet -30 mt -39 mt -130 feet

91 CHAPTER 4 INTRODUCTION In the previous chapter we discussed the readily noticeable changes such as suit compression or the need to equalize the pressure in your ears referred to collectively as the direct effects of pressure. But pressure also produces other effects, which may be less evident but are just as important. These effects occur as a result of the influence of pressure on the gases that make up our breathing mixture while diving. GAS PARTIAL PRESSURES - DALTON S LAW So far we have discussed how a gas behaves without considering its composition. We now need to look at how a gas behaves when it is made up of different elements, and how individual gases behave within a mixture. The English scientist John Dalton was one of the first to examine gas mixtures. He proved that each gas in a mixture behaves as though the other gases do not exist. For example, air is made up of 79% nitrogen and 21% oxygen, so 79% of air pressure is exerted by nitrogen and 21% by oxygen. This phenomenon is known as Dalton s Law. Dalton referred to these individual pressures within a mixture of gas as partial pressures and found that each partial pressure is proportional to the number of molecules of that gas present in the mixture. But how does this affect us as divers? When we breathe air on the surface, we inhale a mixture of 79% of nitrogen and just less than 21% oxygen (we ll ignore the small percentage of inert gas present for simplicity s sake.) We already know that surface pressure is equal to 1 atm (14.7 psi). According to Dalton s Law, oxygen exerts 21% of total air pres- CHAPTER 4 PHYSIOLOGY 89

92 CHAPTER 4 PHYSIOLOGY sure, while nitrogen exerts the remaining 79%. We can then calculate that of the total pressure of 1 atm (14.7 psi), the partial pressure due to oxygen is 0.21 atm (3.1 psi) while the partial pressure exerted by nitrogen is 0.79 atm (11.6 psi). We ve also learned that if we dive to a depth of 10 meters (33 feet), the total pressure will be 2 atm (29.4 psi). If the temperature remains constant, each component of the gas continues to exert its partial pressure in proportion to its percentage. So at 2 atm (29.4 psi), oxygen exerts 21%, or 0.42 atm (6.2 psi), and nitrogen exerts 79%, or 1.58 atm (23.2 psi). Depth Sea Level 10 m 33 feet 20 m 66 feet 30 m 99 feet Absolute Pressure 1 atm 14.7 psi 2 atm 29.4 psi 3 atm 44.1 psi 4 atm 58.8 psi Partial Pressure O atm 3.1 psi 0.42 atm 6.2 psi 0.63 atm 9.3 psi 0.84 atm 12.4 psi Partial Pressure N atm 11.6 psi 1.58 atm 23.2 psi 2.37 atm 34.8 psi 3.16 atm 46.4 psi When ambient pressure increases upon descent, the pressure inside our lungs must also increase to keep their volume constant. So when we take a breath from the regulator at depth, a larger number of gas molecules enter the lungs to maintain their volume Green ball = Nitrogen Black ball = Oxygen 0 meters (0 feet) 1 atm (14.7 psi) 10 meters (33 feet) 2 atm (29.4 psi) (see figures above). Even though the percentages of the gases that make up the mixture do not change, the number of molecules of each gas inhaled increases. This is why the increase in partial pressures becomes a concern. For example, let s assume that while filling a tank, the air is contaminated with a small quantity (1%) of 90

93 Red ball = Carbon Monoxide Green ball = Nitrogen Black ball = Oxygen Air contaminated with Carbon Monoxide 0 meters (0 feet) 1 atm (14.7 psi) 20 meters (66 feet) 3 atm (44.1 psi) carbon monoxide. If we now descend to 20 meters (66 feet), the amount of carbon monoxide breathed at that depth triples. It is now equivalent to breathing a mixture containing 3% carbon monoxide on the surface. So even a tolerable level of contaminants on the surface can become toxic at depth, even though the gas composition of the mixture remains unchanged. GAS DISSOLVED IN LIQUIDS - HENRY S LAW Aside from how gas mixtures behave, we must also understand the interaction of gases and liquids. We are already familiar with examples of gas entering solutions; we know that fish process oxygen that has dissolved in the water and that all fizzy drinks contain dissolved carbon dioxide. This concept can be difficult to comprehend, since to the naked eye, liquid doesn t appear to have spaces for gas to enter. However, we can see evidence of dissolved gas whenever we add ice to a carbonated drink. The bubbles that form are carbon dioxide coming out of the solution. This dissolved gas in the liquid also continues to exert pressure. This pressure inside the liquid is defined as gas tension. The amount of gas that can be absorbed by a liquid and what affects this absorption was studied by one of Dalton s colleagues, William Henry. His experiments proved that the quantity of a given gas that dissolves in a given liquid at a given temperature depends on the partial pressure of the gas and its affinity with that liquid (Henry s Law.) According to Henry s Law, temperature and pressure affect how much gas can dissolve in a liquid. Let s use as an example a glass of water containing no dissolved gas. We then put it in a container in which an absolute vacuum has been created so there CHAPTER 4 PHYSIOLOGY 91

94 CHAPTER 4 PHYSIOLOGY Henry s Law: At a constant temperature, the amount of a given gas that dissolves in a given type and volume of liquid is directly proportional to the partial pressure of that gas in equilibrium with that liquid. 1 atm (14.7 psi) 2 atm (29.4 psi) is no gas in contact with the water. If we introduce air into the container, the air molecules will begin to penetrate into the liquid. This dissolved gas will exert its partial pressure, or tension, according to Dalton s Law. The difference between the pressure of gas in contact with a liquid and the tension of the gas dissolved is called the pressure gradient. If this gradient high, gas is rapidly absorbed by the liquid. But as the molecules of gas dissolve in the liquid, the gradient diminishes and the molecules dissolve more slowly. The gas will dissolve in the liquid until its tension is equal to the pressure of the gas in contact with the liquid. Although molecules will continue to enter the liquid, the same number will exit from it: they will be balanced and the quantity of gas dissolved will not increase. At this point the liquid is said to be saturated. Now let s increase the pressure in the chamber. This increases the pressure of the air in contact with the water and forces a larger quantity of gas to dissolve in the water. Over time, gas will enter the water until its tension in the liquid and the pressure of the air on the liquid are the same (saturation). If we reduce the pressure in the chamber, the reaction is reversed. Now the air dissolved in the water has a greater tension than the air in contact with the water and is supersaturated. Gas exits the liquid until its tension is equal to the pressure of the gas in contact with the liquid. If the pressure of the gas is reduced very slowly, if the liquid is not shaken, or if there are no foreign particles in the liquid, the gas exits invisibly. But if the pressure of the gas is decreased too quickly, Temperature and Pressure Environment Temperature Lower Temperature or the liquid is shaken vigorously or other foreign particles are present in the liquid, the gas exits visibly in the form of bubbles. Besides pressure, temperature also affects the absorption of gas in liquids. Heat speeds up the motion of the molecules in a liquid, and this rapid motion leaves less space for gas molecules. This phenomenon can be observed 92

95 when water is heated and small air bubbles begin to form. This is caused by increased motion of the water molecules pushing out the dissolved molecules of air. In contrast, the colder a liquid is, the more gas that can be dissolved in it. A colder liquid has slower moving molecules, creating space for a larger number of gas molecules. Let s now see how gas in solution and Henry s Law affects us as divers. NITROGEN NARCOSIS AND DECOMPRESSION SICKNESS At sea level, some degree of nitrogen is always dissolved in the blood and other tissues. As you breathe, new molecules of nitrogen enter the bloodstream, while others already present exit in equal number: the system is said to be in a state of equilibrium. When we breathe underwater the regulator provides air at ambient pressure, and as we descend the air breathed from the tank increases. The air in our lungs now exerts a greater pressure on the blood in contact with its alveoli than the tension exerted by the dissolved nitrogen in our bloodstream. So, according to Henry s Law, nitrogen begins to enter the bloodstream and moves to other tissues. (This process applies to oxygen as well, and will be discussed later). Nitrogen Narcosis When the partial pressure of nitrogen dissolved in our tissues increases, there may be neurological effects on the diver under water. You may feel inebriated, euphoric, or start or lose your ability to reason and CHAPTER 4 PHYSIOLOGY 93

96 CHAPTER 4 PHYSIOLOGY make proper choices. Divers have exhibited behaviors such as removing their regulator, attempting to talk, or generally becoming overconfident in their abilities. You may also become disoriented, or ascend too rapidly, risking pulmonary overinflation. This phenomenon is called nitrogen narcosis and, when making deeper dives, for example, beyond 130 feet (39 meters), symptoms such as uneasiness and anxiety may become hazardous. Other symptoms can include auditory or visual hallucinations, memory loss and, in the severest cases, loss of consciousness. Fortunately, we can easily prevent nitrogen narcosis by keeping the partial pressure of nitrogen low. Avoid diving to deeper depths (beyond 80 feet or 24 meters), and do not descend faster than 75 feet (22 meters) per minute. Also, the risk of nitrogen narcosis may be reduced by diving with oxygen-enriched air (Nitrox). The treatment for the symptoms of nitrogen narcosis is as simple as ascending to shallower depths until the symptoms disappear. Decompression Sickness SNSI believes strongly in the advantages of using enriched air while diving, and as we will see below, it can be an important part of preventing decompression sickness. We have learned that while we are underwater, our tissues absorb nitrogen until they are saturated. But not all tissues take the same amount of time for this to happen. Depending on their makeup, some tissues absorb nitrogen and become saturated faster than others. Let us examine what happens when we return to the surface after a dive. Our tissues will now need to release the excess nitrogen absorbed during the dive. This process works in the reverse of the saturation process. When the partial pressure of the gas in the lung decreases either because the pressure of the mixture 94

97 breathed is reduced, or because the ambient pressure decreases this new pressure gradient causes gas to move from the tissues to the blood, and then to the lungs to be exhaled. Just as with absorption, tissues also release nitrogen at different rates. Because tissues are capable of tolerating some degree of oversaturation, we can surface from the dive with some level of extra or residual nitrogen in our tissues. While we re on the surface, nitrogen will continue to be released until its partial pressure returns to normal. If we make another dive before the nitrogen has returned to its normal level, the higher nitrogen level must be calculated into our dive plan. Although our bodies are capable of handling significant and relatively sudden increases in the partial pressure of inhaled gas without harm, decreases are another matter. Decompression sickness (DCS) can occur when the surplus dissolved nitrogen is released so quickly that bubbles form (as we have seen with Henry s Law) in the blood and tissues due to a high pressure gradient. The symptoms can include joint pain, skin rash, numbness, tingling, fatigue and paralysis. They may appear between 15 minutes and 12 hours after the dive, and in some cases even later. In the early 20th century, the Scottish physiologist CHAPTER 4 PHYSIOLOGY 95

98 CHAPTER 4 PHYSIOLOGY John Scott Haldane studied the problem of decompression sickness in Royal Navy divers. His work became the foundation for modern decompression theory and for the first dive tables, which we will discuss later. Although these absorption and elimination processes follow Henry s Law, it becomes much more complex when applied to the human body. There are numerous factors that may affect gas absorption and elimination; so there is no absolute guarantee that decompression sickness will never occur. However, the following techniques may help to reduce this risk. Prevention The most basic strategy is to observe the depth and time limits established for recreational diving. One of these is your ascent speed. The recommended ascent rate in recreational diving is 30 feet (or 9 meters) per minute. By ascending no faster than this rate, excess nitrogen can be expelled through your exhalations without coming out of solution. Halting the ascent briefly by making what s termed a safety stop at 15 feet (or 5 meters) for 3-5 minutes allows even more time for nitrogen elimination, further reducing the risk of DCS. Your dive profile (time/depth combination) is also a concern. You should avoid constantly changing depth throughout the dive, swimming continually from deep to shallow in a saw-tooth pattern. Additionally, you should avoid reverse profiles (diving to a greater depth after time at a shallower depth) and dives involving a rapid descent followed by a rapid ascent. Modern dive tables and computers - which are mathematical models - cannot take these factors into consideration and they therefore could put you at higher risk for DCS. There has been no conclusive evidence tying exposure to the cold to decompression sickness, but many experts believe that low temperature may contribute to the onset of DCS. It is theorized that exposure to the cold causes changes in the circulation which could affect nitrogen exchange in our tissues. Besides wear- 96

99 ing adequate thermal protection, ideally a dry suit in cold conditions, it s advisable to avoid the maximum limits of any dive table or computer. Another important precaution is to avoid becoming fatigued before, during or immediately after the dive since fatigue appears to affect nitrogen exchange. Your diving center and dive boat crew will assist you in loading and unloading tanks, assembling your equipment and helping you enter and exit the water, keeping fatigue and stress to a minimum. Other factors that may affect our circulation are alcohol and dehydration; divers must refrain from drinking alcohol before, during and for a reasonable amount of time after the dive. Also, be sure to drink plenty of non-alcoholic liquids before and between your dives to stay hydrated. The use of enriched air (Nitrox) can also play a fundamental role in preventing DCS as we shall see later in this manual. FIRST AID AND TREATMENT If a diver exhibits symptoms of DCS you must immediately contact the nearest emergency center (911 in the US). Have the diver drink plenty of water, place them in a comfortable position and administer pure oxygen. (Your instructor will elaborate on oxygen administration and the legal consequences of doing CHAPTER 4 PHYSIOLOGY 97

100 CHAPTER 4 PHYSIOLOGY so.) The treatment for decompression sickness often requires recompression in a hyperbaric chamber, and the sooner the better. This reduces the size of the nitrogen bubbles allowing them to return into a solution, and has other physiological benefits. The diver is then depressurized slowly to allow the nitrogen to be exhaled. The need for recompression and the procedures to be used will be determined by the medical staff. SUMMARY ON DCS What is Doppler? In the early days of diving, dive tables were tested using the simple criteria of whether a diver got the decompression sickness or not. That sounds pretty crude, but there was no other option. However, by the 1960s technology made another approach possible using a device called a Doppler Ultrasound Flowmeter, which was developed to monitor blood flow during surgical procedures. It is an acoustical device based on a phenomenon in physics know as the Doppler effect (named for an Austrian scientist, Christian Johann Doppler, who discovered the effect in 1842). The Doppler Detector works by sending ultrasonic waves into the diver s body. These waves reflect back to the monitor, making a distinctive sound according to the density of whatever they encounter. The sounds heard against the constant background noise of the heartbeat and flowing blood indicate moving bubbles. But what does this have to do with decompression sickness and dive tables? Before bubbles grow to a size that causes DCS symptoms, they exist in a smaller silent (asymptomatic) state, and can be detected by the Doppler device. As a result, researchers and dive table designers can use the presence and quantity of these silent bubbles as a rough criteria in testing dive tables, rather than actual DCS symptoms. While no direct correlation between silent bubbles and DCS has been proven, many experts believe that silent bubbles are nonetheless a good indicator of decompression stress, and encourage practices that minimize their presence. Using this logic, dive table developers use Doppler-based testing as a way to increase the effectiveness of decompression models over the older method of symptoms/no symptoms. Decompression sickness is a complex condition; no dive computer or table can completely eliminate the risk of its occurrence. But by understanding the concept of nitrogen absorption and elimination, and taking into account appropriate practices and precautions, it s highly unlikely that you will ever develop Decompression Sickness. THE DIVE TABLES Every dive requires that you consider your maximum depth and length of length of time you may remain at that depth to avoid DCS. To do this, dive tables have been developed. In North America, the US Navy developed the first tables used by scuba divers. Since then several other versions have been developed for recreational divers. By definition, a recreational dive is one where the diver does not exceed the time limit for a particular depth, so that he can always ascent immediately and di- 98

101 rectly to the surface. Staying longer would require a decompression stop, which is a halt in the ascent to allow the body to rid itself of the excess nitrogen. Use of recreational no-stop tables minimizes the risk of DCS, although individual differences prevent any guarantee of immunity. Dive Tables Terminology Before we get into the use of dive tables, we need to know the meaning of the terms used in them: -- No-decompression dive: any dive that allows a direct (no stop) ascent to the surface. -- Surface interval: the time spent on the surface between two dives. -- Repetitive dive: any dive made with a surface interval that does not allow for the complete elimination of the residual nitrogen from previous dives. -- Depth: the maximum depth reached during a dive. -- Dive time: the amount of time from the beginning of your descent to the beginning of your ascent; referred to as ABT (Actual Bottom Time). -- Residual nitrogen: the amount of nitrogen that remains dissolved in the diver s tissues after the dive is ended and gradually eliminated while on the surface. -- Group designation letter: An alphabetic letter in the table indicating the amount of residual nitrogen in your tissues after the dive. -- New group designation letter: An alphabetic letter that indicates the reduced amount of nitrogen present in your tissues after time spent on the surface. -- Residual nitrogen time: The number of minutes, indicated by the new group designation letter, that must be subtracted from the maximum time allowed for the new dive; indicated by RNT. -- Total dive time: The actual dive time plus the residual nitrogen time (RNT) at the end of a repetitive dive, indicated by TBT (Total Bottom Time). CHAPTER 4 PHYSIOLOGY 99

102 CHAPTER 4 PHYSIOLOGY THE SNSI DIVE TABLE The SNSI dive table is actually three tables incorporated into one, each with its own individual function. It was devised by combining the US Navy table for diving on air with the US National Oceanic and Atmospheric Administration (NOAA) Nitrox tables N1 and N2. TABLE 1: Doppler no-decompression limits based on the US NAVY and NOAA tables. Table 1 gives you the time for which you may remain at a given depth and return directly to the surface without decompression. It also gives you the group letter to which you belong at the end of each dive. At the far left of the table you will find the depths for AIR, EAN32 and EAN 36. EAN 32 is Enriched Air Nitrox containing 32% oxygen, and EAN 36 contains 36%. For now, we will only consider diving with air; we will discuss enriched air diving in the next chapter. If you dive to a depth not indicated in the table, you should refer to the next deepest depth. For example, if you dive to 11 meters (36 feet), use the depth of 12 meters (40 feet) for your calculations. TABLE 1 Repetitive Group Designation letter. ARIA 3 4,5 6 7,5 9 10, DEPTH NDL EAN 32 EAN 36 Doppler U.S. Navy NOAA 4,5 6 7, ,5 9 10, No Limit No Limit No Limit Moving up to the right you ll see the abbreviation NDL : these columns indicate the no-decompression limits. The blue column indicates the Doppler limits and the red column indicates the US Navy limits. The remaining part of the table indicates the times you can spend at various depths within the corresponding groups. The times marked with the red line (Doppler curve) are the Doppler limits, while the times indicated in the red area are the US Navy limits. Let s try an example of a planned dive to 15 meters (50 feet). Note the Doppler no-decompression limit is 63 minutes, while the US Navy limit is 92 minutes; recreational divers should always remain within the Doppler limits, which is 63 minutes. However, wanting to be even more conservative, you decide to dive REPETITIVE GROUP DESIGNATION A B C D E F G H I J K L

103 for only 50 minutes. To determine your Repetitive Group after the dive move to the right across the 15 meters (50 feet) row to 56 minutes. (Remember, always use the next highest value if your actual bottom time isn t listed.) Next, move up the column and you ll find that you re in Repetitive Group letter H. TABLE 2: Surface intervals Table 2 allows you to make a second dive but take into account the residual nitrogen still in your tissues from the previous dive. Continuing with the previous example, after remaining out of the water for three hours, you plan a second dive to 12 meters (40 feet). You enter Table 2 at the top and find your original Repetitive Group, which was H. Now move down the column until you locate the timespan containing three hours. Note that in the middle of the eighth row you find the time span of 2:38 and 3:29. As your Surface Interval was three hours, this is where you now change direction and move down the column to find a new Repetitive Group of E. TABLE 3: Residual nitrogen times Table 3 is used to quantify exactly how much residual nitrogen (in minutes) remains in your tissue before your next dive. This must be subtracted from the Allowable Bottom Time. Continuing with the previous example, you are TABLE 2 now in Repetitive Group E and plan to dive to 12 meters (40 feet). Enter Table 3 at the top in the E column and move down to where it intersects the 12 meters (40-foot), blue air column, on the left. There you will find two numbers in the box, 45 on top and 63 on the bottom. The top number indicates the residual nitrogen time (RNT); in this case, 45 minutes. The bottom CHAPTER 4 PHYSIOLOGY 101

104 CHAPTER 4 PHYSIOLOGY number indicates the maximum no-decompression time limit for the next dive. In this case, the diver has a bottom time limit of 63 minutes. Being a responsible diver, you decide to plan for an actual bottom time (ABT) of only 50 minutes, well below the Doppler limit. TABLE 3 TIME TABLE: ARIA EAN 32 EAN ,5 7, A B C D E F G H I J K L PLANNING REPETITIVE DIVES Using the method described for the three tables, you can plan as many dives in a day as you wish. So, let us continue with the previous example, let s find your new Repetitive Group after your second dive. Again, start on Table 1 and follow the Residual Nitrogen Time Adjusted No-Decompression Time Limits Max No-Decompression time limits U.S. Navy/NOAA Tables SCUBA AND NITROX SAFETY INTERNATIONAL meters (40 feet) air depth row. Remember, while your Actual Bottom Time (ABT) was 50 minutes, you must also account for the Residual Nitrogen Time (RNT) of your first dive of the day, which was 45 minutes. This means that while you were only under water for 50 minutes, your tissues actually contain a nitrogen concentration equal to 95 minutes. This is termed your Total Bottom Time (TBT). It s important to remember: ABT + RNT = TBT. To find you new Repetitive Group, move to the right along the 40-foot air depth row until you find either your actual TBT or the next greater number. In this case you ll find the actual TBT of 95 minutes three columns from the end. Now move up the col- 102

105 umn and you find your new Repetitive Group J. This time you decide to spend two hours on the surface and make the third dive of the day to 9 meters (30 feet). Moving on to Table 2 you enter at the J column and move down to the row that contains the timespan of two hours (2:00). Ten rows down and three columns to the left you will see the timespan 1:45 to 2:37, which contains 2:00. Moving down the column you will find your new Repetitive Group of H. You now enter Table 3 at the top in the H row and move down to where it intersects with the 9 meters (30 feet) air depth row. This time the numbers contained in the intersecting box are 108 and 37. Moreover, the top number is your residual nitrogen time and bottom number is your adjusted no-decompression limit. Thus, you could remain under water for your third dive a maximum of 37 minutes (although for added safety you should reduce this time to 30 minutes). As a responsible diver, always plan your dives in advance and remain well within the no-decompression limits. Another helpful tool is to illustrate your dive plan by drawing a dive profile to show your planned depths, dive times, surface intervals and groups. Your SNSI instructor will demonstrate how to use the dive profile contained in your SNSI logbook. CHAPTER 4 PHYSIOLOGY 103

106 THE DIVE COMPUTER CHAPTER 4 PHYSIOLOGY While dive table are helpful devices, they can be tedious, and when using them divers can make mistakes. Fortunately, there s an easier method that s free from any tedium or computational errors, and that is a dive computer. Not surprisingly, dive computers have all but replaced dive tables. Like dive tables, dive computers use theoretical decompression models. But instead of displaying the information in a tabular format, the mathematical data and instructions (termed algorithms ) are programmed into a microprocessor. Then, using the actual time/depth information in real-time, the microprocessor calculates the diver s decompression status continually. 104

107 HOW TO USE THE DIVE COMPUTER While dive computers are wondrous instruments, it is important to remember that they are mechanical devices. Although highly reliable, they can malfunction or run out of power. And, just like dive tables, they are all based on theoretical models, not what is actually going on inside your body. Therefore, using a computer does not guarantee safety, nor is it a license to turn off your brain! Common sense and a good dose of caution are always in order. Consider your dive computer a tool used to make an informed, prudent decision; it provides only some of the information you need to dive safely. You make the final decision, not the device. It s also important to recognize that there are different algorithms programmed into different computers. So, while there are similarities in the data they provide, there can also be substantial differences. This does not mean that some computers are unsafe; it is just that assumptions made by some decompression algorithms differ considerably. Your SNSI instructor can provide specific insight and advice when it comes time to purchase a dive computer. Here are some helpful guidelines on using a dive computer to maximize safety. Read the instruction manual carefully before using a computer, and never rely on the knowledge of others. Like any electronic device, it takes some time and practice to learn how to use a dive computer. Certainly, it is important to carefully read and understand the instruction manual before using it. For example, you must understand the how the information is displayed, how to enter and exit the various modes and settings and what warnings the device can provide (such as too rapid an ascent). CHAPTER 4 PHYSIOLOGY 105

108 CHAPTER 4 PHYSIOLOGY The capabilities of a modern dive computer are quite extensive, and can even enable decompression diving. However, remember that this is beyond the scope recreational diving, and requires not only additional training but a good deal of experience. If you re interested in taking this next step, you can get the required training in a SNSI Recreational Deco Diver course. One diver, one computer It is very important that each diver in a buddy team have his or her own computer. The reason is simple: even though a dive team may plan to stay together, divers never remain exactly at the same depth for the same amount of time. Therefore, the decompression rate of each team member can vary. Respect the ascent rate All computers have an ascent rate of around 9 meters (or 30 feet) per minute. Remember, anytime you ascend you are decompressing, so it s important not to do this too quickly. There s also evidence that a slow ascent can help reduce the development of micro bubbles, which sometimes form when ascending at faster rates. Ascent rate is also an important parameter in how the computer calculates your decompression rate, and exceeding this rate may invalidate the computations. Fortunately, all computers have ascent rate warnings (flashing displays and/or audible signals) to let you know if you are ascending too fast. Do not forget common sense As we have discussed, several factors other than depth and time appear to increase the possibility of DCS. Taking into account factors such as fatigue, dehydration, excessive exercise and even advanced age is highly individual and beyond the capabilities of any general mathematical model programmed into a dive computer (although some computers allow you to select the level of con- 106

109 servatism used in their calculations). Prudent diving means avoiding maximum no-decompression limits, avoiding excessive fatigue or exercise or making too many repetitive dives. Review the allowed time limits All computers allow you to scroll the allowed times at various depths before you dive. It is important to perform this procedure when planning a dive. Also, review and discuss any differences in allowable limits if your buddy is using a different computer model, or has made a repetitive dive that you have not. Follow the more conservative computer Because two computers will almost never indicate the exact same profile, a good safety practice is to follow the more conservative of the two. This requires that you keep a close eye on one another and communicate often. Always make safety stops A safety stop should be a standard part of every dive. Some dive computers build the procedure into their programming, having you halt your ascent at a depth of 3 to 5 meters (between 10 and 15 feet) for 3 minutes at the conclusion of every dive. However, some computers do not have this provision. Even if yours does not require a safety stop as a standard procedure, make one anyway. It can do no harm, and may reduce your risk of decompression sickness. Remember that your last stop is the surface Many divers forget about the final ascent from the CHAPTER 4 PHYSIOLOGY 107

110 CHAPTER 4 PHYSIOLOGY safety stop to the surface, yet this is still part of your dive profile. Be sure to complete your ascent slowly. Consider that, when you re at 15 feet (5 meters), the ambient pressure is 22 psi (1.5 atm); at the surface, it s 14,7 psi (1 atm). Therefore from 15 feet (5 meters) to the surface there will be a reduction in the ambient pressure of 33%. Don t be in a hurry to get your head out of the water, relax and enjoy the last few moments of your dive! Never turn off your computer before complete desaturation The computer must remain on until the nitrogen is totally eliminated. After a series of dives, it is possible that the total desaturation time will be even longer than 20 hours. As a consequence, there will be a gradual reduction of the time allowed on the bottom for subsequent dives. Some computers prevent premature shutdown by not providing a way for the user to turn off the device. Instead, they go off automatically when complete desaturation occurs. Dealing with instrument failure If your dive computer fails during a dive, it s best to ascend immediately, remembering to ascend slowly, and make a safety stop. While it may ruin your dive, computer failure will have no other safety consequence provided you did not exceed the no-decompression limit. This is another reason to check your instruments frequently. Conclusion Electronics have revolutionized the way we dive, substantially lengthening diving times; but the computer is not able to think for itself; it s just a smart calculator. It s your responsibility to use it conservatively and with common sense. Although this instrument will help you safely enjoy diving, you should remember that no computer or dive table can prevent DCS with certainty. All you can do is manage the risk in the most informed way possible. 108

111 THE COMPUTER AFTER DIVING Most modern dive computers allow you to link it to your personal computer (PC) via an interface to download your data. Manufactures often supply analysis software so you can create charts and graphs that enable you to better understand the details of your dive profile. This is an excellent feature that you should not ignore when purchasing a computer. Examples of graphs include: time and depth, parameters related to breathing, tank pressure, temperature and rates of descent and ascent. Divers who use Nitrox can produce diagrams of the Partial Pressure of the Oxygen (PPO 2 ), the level of central nervous system (CNS) toxicity of the breathing mixture, and the Oxygen Toxic Units (OTU). We will cover these topics in the next chapter. In addition, many programs also generate a graph that shows the tissue nitrogen load as a function of the dive time. Once you learn to use the programs for downloading information from the memory of the dive computer and generating graphs, you can compare your data with your diving buddies or for other dives. Some programs have a feature that highlights portions of the profile that are outside normal parameters, which could be a good indication that you should alter your diving practices. For example, a profile analysis may motivate you to be more careful with ascent rates, or avoid wide fluctuations in depth ( saw-tooth profiles). Profile analysis also shows the reality of how buddy teams actually behave under water. The evidence from a computer-generated dive profile often points out the myth of two divers diving side-by-side. In addition to recording dive data and profiles, some computers are useful for dive planning in other ways. For example, some allow you to simulate multi-repetitive dives and generate graphs showing the absorption of nitrogen. These graphs can be very useful for understanding how nitrogen absorption and elimination occurs. This can also help you understand how important it is to carefully plan multiple repetitive dives over consecutive days, such as on a liveaboard holiday. CHAPTER 4 PHYSIOLOGY 109

112 CHAPTER 4 PHYSIOLOGY Many dive computer software programs allow you to add information turning them into what are essentially dive logbooks. You can add information such as buoyancy, air consumption, depth and temperature. You can also customize the program to add emergency contact information, personal information on your buddy, dive site characteristics and even information about diving centers. While some of this may appear unnecessary, it may turn out to be quite useful for future planning and better risk management. Yet another useful application of analysis software is how it can aid data collection to improve safety for all divers. Many researchers now use data collected from individual computers to study both diving accidents and diver behavior so we can better understand and prevent diving accidents and reduce risk. CHSING A DIVE COMPUTER Now that you know what a dive computer is and how it works, you can make a more informed choice about which computer to purchase. All computers on the market today are quite reliable but vary significantly in the features they offer. In addition to the type of decompression model used, dive computers vary in terms of their sophistication. Basic models provide only the essential information on 110

113 decompression status and do not include the PC interface feature. Others have quite an elaborate array of features including probes that detect changes in breathing gas for calculations on dives where multiple gas mixtures are used. (An area of technical diving well beyond this course.) Many models allow for user-selection of decompression models so one can choose a more or less conservative calculation for more or less time under water. Some computers also do more than simply keep track of decompression status, and integrate with your air supply. By doing so they can calculate your remaining bottom time based on either your air supply or decompression status, prioritizing the one putting you closest to the limit. For new divers, the best choice is often a basic, easy-to-use computer with an easily-read, simple data readout. As you gain experience you may find that a more feature-rich device suits your needs better, allowing you to use your basic model as a back-up. One important feature to consider when buying a computer is whether the computer has a user-replaceable battery. Computers that do not allow the user to replace the battery are more expensive to maintain, and less convenient, since the device must be returned to the dive center or manufacturer for battery replacement. CHAPTER 4 PHYSIOLOGY 111

114 CHAPTER 4 PHYSIOLOGY SAFETY PROCEDURES Given the many factors that can affect decompression status, you must be disciplined when planning dives. Remember to make a safety stop of 3-5 minutes at 3 to 5 meters (10 to 15 feet) for all dives below 9 meters (30 feet). When using tables If you plan a dive using the Dive Tables, and you exceed the Doppler no-decompression limits by no more than 5 minutes, you must ascend normally up to 5 meters (15 feet) and stop for at least 10 minutes, or longer if your air supply allows. If you exceed the Doppler no-decompression limits by more than 5 minutes but less than 10 minutes, we recommend you stop at 5 meters (15 feet) for at least 20 minutes or longer if you have enough breathing mixture left to do so. In either case, do not make any additional dives in the following 24 hours. When using a computer If you exceed the no-decompression limits using a dive computer, make all the mandatory stops indicated by the device and an additional safety stop of 3 minutes at 5 meters (15 feet). Remember, even though your computer will allow it, the use of a dive computer does NOT automatically authorize you to make dives beyond the no-decompression limit. Dives that require mandatory decompression stops have a significantly higher risk of DCS and require a high level of experience well beyond the training you will receive in this SNSI Open Water Diver program. Once you have obtained your SNSI Open Water Diver certification, you can attend the SNSI Advanced Open Water Diver course. Only then will you qualify to take the SNSI Recreational Deco Diver course where you will learn how to dive beyond the no-decompression limits. DIVING AT ALTITUDE AND FLYING AFTER DIVING Diving at altitude (over 300 meters /1,000 feet) above sea level) requires special consideration, not the least of which is that most dive tables and decompression models are designed for use at sea level. However, because the ambient pressure at altitude is 112

115 lower, it must be taken into consideration when planning your dive. Reaching your diving destinations often involves flying, which also means a reduction in ambient pressure. Most small aircraft do not have pressurized cabins, so you are exposed to whatever pressure is present at the altitude you are flying. Commercial aircraft normally maintain a cabin pressure equivalent to an altitude of 1,500 2,000 meters (5,000 7,000 feet). The general guidelines to be followed when flying after diving are as follows: When making just one dive a day wait at least 12 hours before flying. When making repetitive dives, especially if for several days consecutively, wait for at least 24 hours. SUMMARY This chapter has discussed the indirect effects of pressure on the diver and how to plan an air dive to reduce your risk of decompression sickness. You have also learned about dive computers and how to choose the right device for your specifics needs. As you learn more, and practice what you learn, you will become a more confident diver capable of handling whatever challenges await you. Diving is fun and serious accidents are quite rare, but understanding what may go wrong - and how to deal with it - is the first step in accident prevention. Watch the SNSI OWD Scuba Skills #3 Video CHAPTER 4 PHYSIOLOGY 113

116 STUDY GUIDE: CHAPTER 4 CHAPTER 4 PHYSIOLOGY 1. What is the oxygen partial pressure of air on the surface? 0.21 atm / 3.1 psi 0.79 atm / 11.6 psi 21% 2. What is the nitrogen partial pressure of the air at 33 feet/10 meters of depth? 0.42 atm / 6.2 psi 79% 1.58 atm / 23.2 psi 3. The recommended ascent rate for recreational diving is: 18 meters / 60 feet per minute. 15 meters / 50 feet per minute. 9 meters / 30 feet per minute. 4. Residual nitrogen is the amount of nitrogen dissolved: in the diver s tissues after the dive. in the diver s tissues before the second dive. Both. 5. For all dives below 9 meters / 30 feet, remember to make a safety stop of: 3-5 minutes at 3 to 5 meters /10 to 15 feet minutes at 3 to 5 meters / 10 to 15 feet. 3-5 minutes at 6 to 9 meters / 20 to 30 feet. 6. You can exceed the no-decompression limits using a dive computer: True. False. 114

117 CHAPTER 5 NITROX OPTION

118 CHAPTER 5 NITROX 116

119 CHAPTER 5 INTRODUCTION In this chapter, we will discuss the differences between diving with air and diving with Oxygen Enriched Air (Nitrox), and explore its advantages. We will also cover the basics of planning and executing a Nitrox dive. This information will enable you to make dives using Nitrox, within the guidelines for SNSI certified Open Water Divers. However, it is not a substitute for the SNSI Nitrox Diver course in which the concepts of Nitrox diving are discussed in much greater depth. WHAT IS NITROX? By definition, Nitrox is any gas made up of a mixture of nitrogen and oxygen. We could say that we re actually breathing Nitrox (also termed normoxic ) as we read this manual. But in underwater diving terms, Nitrox more commonly refers to a mixture containing a larger amount of oxygen than in the air that we normally breathe. The term Enriched Air Nitrox or EANx is used in recreational diving, with the x standing for the percentage of oxygen in that particular Nitrox blend. Two standard mixtures have been established by the National Oceanic and Atmospheric Administration (NOAA): EAN32 (32% oxygen) and EAN36 (36% oxygen), also referred to as N1 or NN1 and N2 or NN2, respectively. Using our knowledge of Dalton s Law, we can examine how the pressures exerted by the two gases (nitrogen and oxygen) vary with changes to their percentages within a mixture. At a pressure of 1 atm (14.7 psi) using a N1 mixture, oxygen exerts a partial pres- CHAPTER 5 NITROX 117

120 Depth Sea Level 33 feet / 10 meters 66 feet / 20 meters Absolute Pressure AIR N1 - EAN32 1 atm / 14.7 psi 2 atm / 29.4 psi 3 atm / 44.1 psi O 2 N 2 O 2 N 2 O 2 N atm / 3.1 psi 0.79 atm / 11.6 psi 0.42 atm / 6.2 psi 1.58 atm / 23.2 psi 0.63 atm / 9.3 psi 2.37 atm / 34.8 psi 0.32 atm / 4.7 psi 0.68 atm / 10.0 psi 0.64 atm / 9.4 psi 1.32 atm / 20.0 psi 0.96 atm / 14.1 psi 2.04 atm / 30.0 psi N2 - EAN atm / 5.3 psi 0.64 atm / 9.4 psi 0.72 atm / 10.6 psi 1.28 atm / 18.8 psi 1.08 atm / 15.9 psi 1.92 atm / 28.2 psi CHAPTER 5 NITROX sure of 0.32 atm (4.7 psi), while nitrogen exerts a partial pressure of 0.68 atm (10.0 psi). Using a N2 mixture, oxygen exerts a partial pressure of 0.36 atm (5.3 psi), while the nitrogen pressure is 0.64 atm (9.4 psi). Now, if we compare the partial pressures of the three gases (air, N1 and N2) at a depth of 20 meters (66 feet) at a total pressure of 3 atm (44.1 psi), we see that nitrogen exerts less pressure when Nitrox is used. In fact, when we breathe normal air, the partial pressure of oxygen is 0.63 atm (9.3 psi) and nitrogen is 2.37 atm (34.8). With 32% Nitrox (N1), the partial pressure of oxygen is 0.96 atm (14.1 psi) and nitrogen is 2.04 atm (30.0 psi). With 36% Nitrox (N2), the partial pressure of oxygen is 1.08 ata (15.9 psi) and nitrogen is 1.92 atm (28.2 psi). The decreased pressure of nitrogen means that less is absorbed. Therefore, the real advantage of Nitrox is not the effect of oxygen but the reduction in nitrogen the extra oxygen provides. Of course, less nitrogen will likely mean less risk of both nitrogen narcosis and decompression sickness. 118

121 A LITTLE HISTORY HOW THE AIR IS ENRICHED The use of Enriched Air Nitrox (EANx) is not new. Its use in diving dates back to the 1950 s but it was not until 1970 that NOAA began to experiment with its use in underwater operations. These studies led to the production of NOAA Nitrox 1, a standard breathing mixture consisting, as mentioned previously, of 32% oxygen and 68% nitrogen. In 1990, they established a second standard mixture NOAA Nitrox 2 containing 36% oxygen and 64% nitrogen. At the same time, NOAA published dive tables for EANx, which allowed dive times longer than those for atmospheric air. EANx was first used in recreational diving under the auspices of diver training organizations with specific Nitrox Diver courses, including the SNSI system. For years, divers went to diving centers to have their tanks filled with air. It is a simple procedure: the tank is connected with a hose to an air compressor, and air is pumped into the tank after being filtered to remove moisture and impurities. Although highly compressed, the air in the cylinder has the same nitrogen/oxygen ratio as atmospheric air. However, filling a tank with Nitrox is a bit more complex. Although nitrox divers can use gas mixtures as high as 40% oxygen, SNSI recommends using a mixture of not more that 36% (N2). The methods most commonly used for producing EANx are the Partial Pressure technique and the Membrane System. The Partial Pressure technique uses pure oxygen. Since pure oxygen under certain conditions is very dangerous, this method requires specialized training. CHAPTER 5 NITROX Nitrox Filling Station Membrane System 119

122 CHAPTER 5 NITROX Never try this on your own! It involves placing a small quantity of pure oxygen into the tank, then filling remainder of the tank with atmospheric air as you would normally from a compressor. Mixtures ranging from 22% to 99% of oxygen can be produced, with technicians using special mixing tables or mathematical calculations to determine the amount of pure oxygen required to obtain a specific EANx mixture. Mixing may be performed one tank at a time, or the mixtures can be prepared in advance and stored in special tanks to allow single tanks to be filled more quickly. Due to the risk of explosion, extreme care and attention to detail are warranted whenever pure oxygen is used. The equipment used also must be specially cleaned and certified to be oxygen-compatible, and the compressor air requires additional filtration beyond the norm. Because of these additional precautions, using Nitrox from a Specialized Nitrox Filling Center provides a guaranteed breathing mixture with a degree of purity that can surpass compressed air. Producing EANx by the Membrane technique works in exactly the opposite way to the Partial Pressure technique. Instead of adding pure oxygen to atmospheric air to increase the percentage of oxygen, the Membrane system eliminates a percentage of nitrogen. The compressor pumps atmospheric air through a set of special membrane filters that remove a predetermined quantity of nitrogen. As the nitrogen is removed, the percentage of oxygen increases. Regardless of method, the final EANx mixture is the same. The EANx produced using the Membrane system is sometimes referred to as DNAx (Denitrogenated Air). NITROX COMPATIBLE EQUIPMENT Due to the increased levels of oxygen present in the mixture, any cylinder and valve used to hold EANx must be Nitrox compatible. Nitrox compatible cylinders are marked with a green and yellow band and are used for Nitrox only. Because the silicone grease and rubber O-rings normally used in regulators may deteriorate if exposed to high levels of oxygen, they must be Nitrox-compatible as well. To address these issues, many manufacturers produce equipment specifically for Nitrox use. Regulators used for air require special cleaning to eliminate contaminants such as oil and lubricants that are not compatible with high percentages of oxygen. Specialized Nitrox Filling Center 120

123 PROBLEMS RELATED TO BREATHING OXYGEN AT HIGH PARTIAL PRESSURES A common misconception is that EANx allows you to dive deeper. However, the opposite is true; you cannot dive as deeply on EANx as you can on air. This reduction in depth is due to the increased oxygen level. Using Dalton s Law, a diver using Ean36 to a depth of 30 meters (100 feet), where the ambient pressure is 4 atm (58.8 psi), breathes oxygen at a partial pressure of 1.44 atm (21.2 psi), 36% of 4 atm (58.8 psi), which is about 50% higher than when breathing pure oxygen on the surface. How can oxygen be harmful if it is essential for life? It turns out that oxygen is a very tricky gas, especially when breathed at higher pressure. Experiments in 1878 by the French physiologist Paul Bert described convulsions caused by oxygen at increased pressure due to its effect on the central nervous system. This is termed Acute Oxygen Toxicity or sometime just Oxtox. (There is also a form of chronic or low-pressure/long-duration oxygen toxicity, but this isn t relevant to divers except during treatment in a recompression chamber). The symptoms of oxygen toxicity at high partial pressures include: muscle tremors, visual disturbances, hearing impairment, nausea, irritability, dizziness and seizures. Since there is no gradual progression from minor symptoms to the CHAPTER 5 NITROX 121

124 CHAPTER 5 NITROX extremely serious condition of convulsions, we must deal with oxygen toxicity through prevention. Just as with decompression sickness, this involves proper dive planning. On the back of the SNSI table you will find the time limits for exposure to oxygen at high partial pressures on the CNS% and UPTD Table (upper left). You will also find the depth limits for the maximum partial pressure (PpO 2 ) of oxygen on the table Oxygen Partial Pressures Tables for Various Depths (upper right). For the two EANx mixtures used in this course, you must determine the depth and time limits that prevent risk of oxygen toxicity. Although the maximum partial pressure of breathable oxygen established by the US Navy and NOAA is 1.6 ata (23.5 psia), the SNSI limit for recreational diving with EANx is 1.5 ata (or 22.0 psia). This limit reduces the partial pressure of oxygen to 80% of the NOAA limits. The EANx depth limit, or Maximum Operating Depth (MOD) is 36 meters (120 feet) for EAN32 and 30 meters (100 feet) for EAN36. However, for Open Water Divers, the depth limit remains 18 meters (60 feet) regardless of the mixture used. Exceeding the Maximum Operating Depth exposes you to the serious risk of oxygen toxicity, which may lead to convulsions and possible drowning. Although exposure to high levels of oxygen for long times at depth may contribute to oxygen toxicity, this problem does not arise when diving according to the SNSI guidelines for using EANx. Looking at the CNS percentage table, you will see that toxic levels of oxygen are possible at a partial pressure of 1.5 ata or 22.0 psi for a 120-minute dive. Using EAN36 at 30 meters (100 feet), the oxygen partial pressure is just under 1.5 ata. If you now look at Table 1 on the reverse side, you see that the Doppler no-decompression limit at 30 meters (100 feet) with EAN36 is 28 minutes. It is therefore impossible to reach the limits of exposure time for oxygen toxicity. The benefits of diving with EANx vary according to the purpose of your dive. For technical dives, the increase in bottom time without exceeding the no-decompression limits in the EANx tables is considered 122

125 the biggest advantage. For example, we can see in Table 1 that a dive on air to 21 meters (70 feet) will result in the same nitrogen absorption as a dive with EAN32 to 24 meters (80 feet) and a dive with EAN36 to 27 meters (90 feet). As an example, your no-decompression limit on air at 21 meters (70 feet) is 37 minutes, but on EAN36 your no-decompression limit is 63 minutes. However, for recreational divers, the most important 3 4,5 6 7,5 9 10, benefit of diving with enriched air is a greater margin of safety. Since enriched air contains a higher percentage of oxygen, the percentage of nitrogen for absorption is decreased, which also decreases the risk of developing decompression sickness and nitrogen narcosis. It follows that you can gain an additional margin of safety by breathing EAN32 or EAN36, but using the bottom time limits of the standard tables for air or a computer programmed for air. This allows you to absorb less nitrogen than you would if breathing air, rather than EANx, under the same conditions of depth and time. This is particularly beneficial for divers with a potentially higher risk of DCS such as elderly or obese individuals, heavy smokers, ARIA 1 DEPTH NDL EAN 32 EAN 36 Doppler U.S. Navy NOAA 4,5 6 7, ,5 9 10, No Limit No Limit No Limit OPEN WATER DIVER and less physically fit divers. Additionally, most divers using enriched air feel less tired after the dive, especially when making repetitive dives over consecutive days. DIVING WITH EANx Planning the dive with enriched air begins with your choice of EANx mix when you are having your tanks filled. After filling, the contents must be analyzed by the user to confirm the oxygen percentage. This will be further certified by an EANx label to the tank. The label must contain the following information: the percentage of oxygen in the mixture (which may TABLE 1 REPETITIVE GROUP DESIGNATION A B C D E F G H I J K L CHAPTER 5 NITROX 123

126 CHAPTER 5 NITROX have a tolerance of +/ 1%) depending on the mixture, the percentage of nitrogen, the Maximum Operating Depth (MOD) for that mixture, and the date and name of the person who analyzed the tank, which must be the user. Portable oxygen analyzers are normally battery powered with a digital read-out, and are attached either to the low pressure hose or directly to the tank valve. Any refilling center or boat that uses EANx must provide an analyzer. Never use an EANx tank if you have not personally analyzed its contents. SNSI SAFETY LIMITS FOR USING NITROX Diving with Nitrox using the NOAA Nitrox tables has an excellent safety record. But SNSI has created tables for its recreational diving certifications that help to simplify dive planning with an approach similar to the recreational tables for air. In addition, we have established rules for planning enriched air dives intended to increase the safety of recreational divers. They are as follows: -- The maximum dive time for a single Nitrox dive must be 120 minutes, regardless of the depth reached and the EANx mixture used. -- For repetitive dives, the maximum bottom time 124

127 must not exceed 180 minutes within 24 hours, regardless of the depth reached and the EANx mixture used. -- The maximum depths for Nitrox dives: 36 meters (120 feet) for N1 and 30 meters (100 feet) for N2. -- The surface interval between two Nitrox dives, regardless of their profiles, may not be less than 2 hours (120 minutes). -- If the maximum allowed time is reached over a period of 24 hours during repetitive dives with Nitrox, you must wait 12 hours on the surface before making the next dive, regardless of the residual nitrogen time. -- It is strongly recommended that you make no more than two Nitrox dives per day. If you make a third dive, it should be with air, and to a maximum depth of 15 meters (50 feet). -- It is important not to confuse the no-decompression limits with the time limits for exposure to high partial pressures of oxygen. -- If unexpected conditions arise or an increase in carbon dioxide is suspected (fatigue, stress, cold), the depth of the dive should be halved and the dive be terminated if the problem persists. SUMMARY The information contained in this chapter should enable you to evaluate the advantages and disadvantages of using enriched air. After you have received your Open Water Diver certification with the Nitrox option, you ll be able to choose between diving with regular air or enriched air, depending on your situation and preferences. OPTIONAL: If You used Nitrox during two of the open-water training sessions, You will have qualified to be certified as a SNSI Open Water Nitrox 32 Diver. X CHAPTER 5 NITROX 125

128 STUDY GUIDE: CHAPTER 5 CHAPTER 5 NITROX 1. What is the oxygen partial pressure of the EAN32 on the surface? 0.21 atm / 3.1 psi 32% 0.32 atm / 4.7 psi 2. What is the nitrogen partial pressure of the EAN32 at 33 feet/10 meters of depth? 1.32 atm / 20.0 psi 79% 0.64 atm / 9.4 psi 3. A dive on air to 50 feet/15m. will result in the same nitrogen absorption as a dive with EAN32 to a depth of: 18 meters / 60 feet. 21 meters / 70 feet. 12 meters / 40 feet. 126

129 CHAPTER 6 THE UNDERWATER ENVIRONMENT

130 CHAPTER 6 ENVIRONMENT SCUBA AND NITROX SAFETY INTERNATIONAL A Project for 128 Marine Life deserves Our Respect; We are temporary Guest in their Environment. As a Scuba Diver you promise to: USE all gear appropriate for your dive, and in perfect working condition. PLAN your dive, and dive your plan. ALWAYS DIVE with a buddy, and abide by proper buddy rules. WEAR the proper amount of weight. CHECK your instruments often. NEVER EXCEED the no-decompression limits. MAINTAIN proper buoyancy. ASCEND slowly. STAY in adequate physical condition, and practice your skill level. RESPECT other divers and the environment. Underwater Life

131 INTRODUCTION About 71% of the Earth s surface is covered with water, so opportunities to go diving abound. However, every aquatic habitat is different, and becoming familiar with these habitats - including their residents - will help you better appreciate your under water experience. While this chapter is relatively comprehensive it s still just an introduction, and cannot prepare you to dive everywhere. It is always best to seek an orientation to any new environment from those with local knowledge such as a Diving Center or other professionals. TEMPERATURE AND VISIBILITY Temperature and visibility underwater are two important factors that determine the difficulty or ease CHAPTER 6 of a dive. Of course, it s easier to dive in clear, warm water, since you ll need less exposure protection and are less likely to become lost or disoriented. Although equally satisfying, diving in cold water and more turbid water is a bit more challenging given the need for additional exposure protection and the decreased visibility. Water temperatures vary, depending on the dive site, anywhere from about 2 C (28 F) in sub-polar locations to nearly 32 C (90 F) in the tropics. Regardless of temperature, some form of exposure suit is always a good idea, even in tropical water. Many are surprised to find that temperatures below 26 C (80 F) - a very comfortable air temperature - are quite uncomfortable for any extended period in the water. Below 21 C (70 F) full exposure protection is essential. One rule of CHAPTER 6 ENVIRONMENT 129

132 CHAPTER 6 ENVIRONMENT thumb is to always wear more exposure protection than you think you ll need because water will drain heat from you about 25 times faster than air. Deeper water also tends to be colder - sometimes very much so - making exposure suit selection more challenging. This is because of a phenomenon known as a thermocline. Water that differs in temperature also differs in density, and the denser water (normally the colder) sinks while the warm water rides on top. So, an exposure suit that might be perfectly adequate for surface temperatures might be completely inadequate for deeper water at the same location. Extreme thermoclines are generally found in temperate regions, but even in the tropics deeper water is often somewhat colder than on the surface. Your local Diving Center can help you select the proper suit for your location. Visibility is another environmental factor that can have a major influence on your dive. The most serious concern is how the lack of visibility may contribute to disorientation or getting lost. Factors affecting visibility include the type of bottom, water movement, seasonal variations, tides and weather conditions. There are specialized techniques for diving in conditions of limited visibility, which are discussed in the SNSI Advanced Open Water Diver course. You should avoid diving in limited visibility until you are more familiar with these techniques. Even very good visibility can be problematic. Very clear water can sometimes lull a diver into descending deeper than they realize. Under such conditions it s important to check your instruments frequently to confirm your depth, and to be sure that you are not descending too quickly. Regardless of the visibility, dive buddies should always remain in close proximity - close enough to respond effectively to an emergency. If you become separated and can t see your buddy, look around, below, and above you for about one minute. If you still can t see your buddy, return to the surface. If both buddies follow this procedure, you will find each other on the surface. 130

133 WAVES AND BREAKERS Waves are caused by wind blowing on the surface of the water. The height of the waves depends on the speed of the wind, its duration and the distance over which the wind blows (fetch). When the wind blows over a calm sea, small waves form on the surface. If the wind continues to blow, these waves become higher and the wind transfers more energy to the water. If there is an increase in the duration, speed and fetch, larger waves form and gradually become more regular. These waves will be of a similar size and will tend to move together at the same speed. Wave energy is concentrated on the surface and in shallow water. As depth increases, the energy begins to dissipate, eventually disappearing all together. Wave energy is greatly absorbed when the waves break on shore. As waves approaches a shore, water near the bottom encounters friction from the seabed while the water near the surface does not. This disparity in speed, and increasing wave height, eventually destabilizes the wave causing it to break (surf). TIDES AND CURRENTS Tides are caused by many factors including bottom topography and current, but the most significant contributors are the gravitational attraction of the moon and, to a lesser degree, the sun. Tidal range can vary CHAPTER 6 ENVIRONMENT 131

134 CHAPTER 6 ENVIRONMENT from a few inches to more than 40 feet, depending on where you are on earth. For divers it s important to understand the effect of tidal currents as they can be very strong, and capable of carrying away even a strong swimmer. Predicting tidal current can be tricky and often requires local knowledge. For this reason it s best to consult a local Diving Center with experience at any specific dive site. They can provide information on how and when to time your dive to slack water, the period when tides are reversing so there s little or no current. Not all currents are caused by tides. Some are permanent ocean circulation currents caused by the rotation of the earth, and their patterns can be complex. You must always consider the potential effect of currents anytime you plan a dive in the open ocean. Trying to swim against even a mild current can be difficult, and impossible against a strong one. When shore diving, you must always plan your entry and exit points in consideration of currents and how they may change over the course of a dive. If you do find yourself caught in a current, don t fight it. You can never win a battle with the sea. Inflate your BC, relax and signal for assistance. UNDERWATER LIFE For most, the main reason we dive is to witness firsthand an entirely different world we could never otherwise experience. But to fully appreciate this new world you need a little knowledge. Itis not unlike going on a holiday. The more you know about your destination, the more you will enjoy the trip. Yet another reason a basic knowledge of the underwater world is useful for divers 132

135 is that, the more you know, the less likely you will encounter problems or engage in behaviors that are detrimental to the environment. This section is not intended to be a comprehensive guide to marine life; only an introduction. But hopefully what is presented here will motivate you to continuing learning more about the subjects that are most relevant and interesting to you. The goal is to appreciate that, while diving involves certain skills and technical knowledge, understanding the environment in which divers function is just as vital to a safe and enjoyable dive. Understanding Marine Habitats One way to appreciate any marine environment is by first understanding that it provides a home (habitat) and occupation (niche) for its residents. Furthermore, the physical setting in which creatures live, and conditions they are subjected to, determine what organisms can live where. Some of the basic conditions that regulate the distribution of marine organisms are light, temperature, nutrient availability, substrate (bottom type) and hydrodynamics (waves and currents). Light can penetrate for hundreds of feet underwater, depending on the clarity, but color diminishes very quickly, beginning at the red end of the spectrum. In deeper water, even if it is very clear, everything appears in a monochromatic blue. This is why a dive light should be a standard part of every diver s kit. Reduced light is bad news for any light-dependent creature, so as you dive deeper you ll find fewer and fewer photosynthesizing organisms (plants and algae). This is one reason that of the hundreds of thousands of flowering plants on earth, very few live in the sea. Some algae can deal better with the diminishing light, but eventually all come to their limits. Another important factor is substrate or the type of bottom present. Normally, it s either soft sediment (sand and mud) or rocky (natural or biological). Generally, rocky bottoms are much more interesting to divers than are soft bottoms. The reason is that creatures such as corals, sponges, al- CHAPTER 6 ENVIRONMENT 133

136 CHAPTER 6 ENVIRONMENT gae, gorgonians, bryozoans (each discussed later) can not burrowing into rock, but can easily attach to it. In turn, their presence provides more attachment points and habitat for other creatures. Rocky bottoms provide more living and hiding spaces, so they tend to be more diverse - and certainly more interesting - than soft-bottom communities. This is particularly evident on tropical coral reefs where life is so abundant that it s astounding. Water motion, in the form of currents and waves, is also an important controlling factor. Plankton suspended in the water column is a vital food source and is distributed by water motion. Upwelling currents can bring nutrients, normally sequestered in deeper water, into sunlit surface waters where photosynthesizing plankton can initiate the ocean food web. Currents also determine the distribution of any organism that broadcasts their fertilized eggs into the water. THE PRINCIPLES OF CLASSIFICATION We do not really know how many organisms exist on earth (estimates range from 30 to 100 million), but so far science has identified and described fewer than two million. In organizing life on earth we need a way to categorize organisms. Ideally, this system should also reflect whether and how one organism is related evolutionarily to others. Equally important, given the number of languages spoken on earth, communicating this organization across language barriers is a concern. Furthermore, many of the same organisms go by different local names. To avoid confusion and misunderstanding, science has a system of classifying every organism by using two names; a genus (always capitalized) and species (never capitalized). Humans, for example, are Homo sapiens while the creature known to many as a bottle- 134

137 nose dolphin is Tursiops truncatus. Names are derived from Latin and ancient Greek because these are dead languages, and not subject to change. The system is also more than just a way to name things; the name is also a clue as to how the organism fits into the evolutionary scheme of life. The genus and species are just the end points in a hierarchical system in descending order from domain, kingdom, phylum, class, order, family, genus and species. Each of these categories is referred to as a taxon (plural, taxa). Marine Algae Algae are the most common plant-like organisms in the ocean. Taxonomically, plants are multicellular organisms within the Kingdom Plantae, while all alga are classified within an entirely different Kingdom, Protista. Regardless, the term algae has no real classification value, but indicates a group of single-cell and multi-cell organisms with different life histories and structure. Commonly, marine plants are referred to as seagrass while marine multicellular algae are termed seaweed. All algae have photosynthetic pigments, like plants, but have no roots, stems or leaves. Some algae are unicellular and compose a major part of the ocean s planktonic community, while larger multicellular algae are more plant-like and live attached to the bottom. What is referred to as the stem of a plant in an alga is called the stipe; the root is the holdfast; and the leaf is called a thallus. In many species of kelp (brown algae) the thallus may reach a length of tens of feet, and grow nearly a half-meter a day! Algae also have different shapes according to the species and may be filamentous, erect, laminar, branched or CHAPTER 6 ENVIRONMENT 135

138 CHAPTER 6 ENVIRONMENT fouling (like on the bottom of boat). Algae are divided into three main groups or divisions, based on their photosynthetic pigments: Rhodophyta (red algae), Phaeophyta (brown algae) and Chlorophyta (green algae). Many red algae secrete limestone (calcify) and therefore are rigid rather than supple. Their color is not always red, but may be pink, violet and even whitish. This depends on the proportions of which the pigments are present in their tissues. The color may vary within the same species according to its stage of development or the environment in which it lives. There are over 4,000 species of Rhodophyta, many of which are economically important both as food products and for their derivatives (the agar used in laboratory cultures or carragenin in some sauces and meat substitutes). The brown algae contain abundant photosynthetic pigments called carotenoid and xanthophyll. When combined with the presence of two types of chlorophyll, a and c, different color variations ranging from golden to greenish to brown are seen. The shape of brown algae varies from filamentous to highly complex forms. Another well-known marine brown alga is sargassum. Some species of sargassum float free on the sea surface, rather than attach to the bottom. There are also some species of brown algae that are economically important for the substances they contain, particularly alginates, which are used in making products such as ice cream, gelatin and syrup. The green algae are more similar to terrestrial plants because they possess the most chlorophyll, a and b, together with other carotenoids and xanthophyll. They also have 136

139 cells with cellulose walls and use starch as a reserve substance. There are about 7,000 species of Chlorophyta, including those used in food. Marine Plants Plants are distinguishable from algae in that they have roots, stems, leaves and even flowers and fruits. Unlike algae, marine plants can draw nutrients from the sediment in which they root, and distribute it throughout the plant. Although there are far fewer marine plants than marine algae, seagrasses comprise highly productive communities and are extremely important both ecologically and economically. Aside from their role as a food source, seagrasses provide vital habitat for a vast number of marine species, and their meadows help prevent coastal erosion. Sponges Poriferans, or sponges, are the oldest multicellular animals, dating back to the Cambrian period 485 million years ago. There are more than 10,000 species of these ancient sessile (living attached to the bottom) creatures. They often have no defined shape, and do not possess organs, but are made up of layers of cells. They also secrete hard, stiffening structures shaped like needles or fibers called spicules. These perform a supporting function and are bound together by a collegen protein compound called spongin. Poriforans are divided into four classes: Hyalospongiae, Calcispongiae, Sclerospongiae and Demospongiae, the Oscolum Porifera body structures Sponge most numerous. The body of a sponge, which may be soft or quite stiff, is divided into cavities with varying degrees of complexity, while the outer surface is typically porous. The vast number of small holes (ostia) enables sponges to filter enormous volumes of water, up to 10 to 30 thousand times their volume per day! An in-current water flow is maintained via tiny flagella (tail-like structures) rotated by specialized cells called choanocytes. In this way sponges get both oxygen and food (bacteria and organic particles). Water is expelled through larger pores called oscula. Cnidarians Cnidarians (the name originates from a Greek word meaning nettle ) are marine animals including the CHAPTER 6 ENVIRONMENT 137

140 CHAPTER 6 ENVIRONMENT sea anemone, jellyfish and coral. Their circular body form is termed radially symmetrical and occurs as either a bag-like polyp or jellyfish-like medusa. The polyp is fixed to a substrate, with its mouth facing upwards surrounded by a variable number of tentacles. The medusoid form is mobile, and has the shape of an umbrella with tentacles along the edge, with its mouth facing downwards. In both forms, the mouth opens to a chamber called a coelenteron (which is why these creatures were once known as Coelenterates). Cnidarians can change shape and appearance. This is very evident in sea anemones, which change shape drastically depending on conditions. The unifying characteristic of all Cnidarians is the presence of stinging cells (cnidocytes) arrayed in large numbers throughout their tentacles. Reproduction is sexual and asexual (gemmation and fission). Some Cnidarians exhibit what s termed alternation of generation, which means that at some life stages it s a medusa and at other times it s a polyp. Many Cnidarians, like corals, only occur as polyps and form colonies of identical copies or clones. Others, like Portuguese man-of-war, are made up of individuals with different specialized functions (defense, nutrition, reproduction). There are about 10,000 known species divided into four classes: Hydrozoans, Scyphozoans, Cubozoans and Anthozoans. Gonad Jellyfish Jellyfish Ephyra Larva Gonad Mouth Manubrium: stalk-like structure hanging down from the center of the underside, with the mouth at its tip. Polyp strobilates Polyp grows Medusa grows 138

141 Anthozoans are the bestknown group because they comprise the sea anemones and most corals. They re divided into two large subclasses, Octocorallia (soft corals) and Hexacorallia (hard corals), which may be distinguished by the number and type of tentacles. The former have polyps with eight tentacles (or multiples of eight) while the latter have six tentacles (or multiples of six). The small phylum Ctenophora comprises marine organisms with a similar appearance to jellyfish, but distinguished by the lack of stinging tentacles. They instead feed by tiny hair-like projections (cilia) arranged like teeth on a comb (hence their common name, comb jellies). The undulation of these cilia often creates an beautiful reflective rainbow-like lighting effect. They are mainly planktonic and comprise about 100 species grouped into two classes. Marine worms Although the term worm has no meaning from the classification standpoint, it is nonetheless one most people understand as a descriptor for a wide range of marine organisms. Divers are most likely to encounter two categories of worms: flatworms (phylum Platyhelminthes) and segmented worms (phylum Annelida). The flatworms have, of course, a flattened body with an obvious head. They are hermaphroditic (produce both eggs and sperm) and reproduce both asexually (by fission) and sexually. There are about 25,000 known species grouped into three classes of which the class Turbellaria is most commonly found in the sea. Due to their bright colors and their size (from 0.40 to 4.00 inches 1 to 10 cm), flatworms are often mistaken for the unrelated nudibranchs (a Mollusc). Flatworms are distinguished from CHAPTER 6 ENVIRONMENT 139

142 CHAPTER 6 ENVIRONMENT nudibranchs by having no significant external structures (gills) except for a pair of tiny tentacles on their heads. They feed on small organisms and consume detritus (decaying organic matter). Segmented marine worms (Annelida) are similar in structure to the common earthworm. Their body is divided into segments (metameres), which are set along the longitudinal axis of the body. A common characteristic is that individual segments of annelids contain a variable number of tufts or bristles. The musclular control of each metamere allows it contract or relax in a coordinated manner to produce the typical movement of all segmented worms. They reproduce sexually. Most marine annelid worms belong to the class Polychaeta. Within this class divers are mostly familiar with the spectacular Christmas tree worm (Serpulidae) and their relative, the feather-duster worm (Sabellidae). Both project beautiful feeding appendages Caphopods into the water, removing them in the blink of Bivalves an eye when disturbed. Gastropods (nudibranch) Molluscs The phylum Mollusca includes most shelled animals like cowries, limpets, clams and mussels. It also contains members that lack shells entirely. Oddly, this group also includes cuttlefish, squid and octopus. Therefore, it s one of the most complex and varied animal kingdoms, and with more than eight classes of 80,000 species, it s the largest marine phylum, accounting for about 23% of all named marine organisms. Generally, molluscs are soft-bodied animals with a distinguishable head, developed to a varying degree, a foot, with a shape differing from one class to another and a mantle, a fold of tissue covering all the internal organs and part of the foot. Many feed using a radula, an Polyplacophorans organ studded with hard tooth-like structures that work like a rasp, to drill through shells (for predators) or scrape the substrate for algae. Molluscs have a heart, a Cephalopods (octopus) circulatory system, complex reproductive and excretory organs and comb-shaped gills 140

143 Rhinophores: Sensory Organs Branchial Plume (ctenidia), which in some groups like the nudibranchs may show great variety. Molluscan reproduction is sexual but individuals can be male, female or hermaphroditic. Chitons (Polyplacophorans) and tusk shells (Scaphopods) are the some of the strangest molluscs. Chitins have a flat foot suitable for slithering and a special shell made up of a series of overlapping calcareous plates; while tusk shells are distinguished by a tubular shell, open at either end, which often takes the form of an elephant s tusk. Molluscs in the class Gastropods ( stomach foot ) include familiar snail-like species such as cowries and conchs. Their foot is a large slithering locomotive organ located under the stomach ( gaster in Ancient Greek). Most Gastropods have twisted internal organs reflected by the typical spiral-shaped shell. Their shells are often very ornate, yet completely absent in some species such as the nudibranchs. Lacking the protection of a shell nudibranchs adopt alternative defensive systems such as producing toxic or noxious-tasting compounds within tissue. Bivalves (clams, oysters, mussels) have a shell that consists of two hinged halves or valves. They control opening the valves via a strong muscle that connects the two halves. Relaxing the muscle allows them to open the valves. Unlike the crawling gastropods, bivalves live a sedentary life with no need for a well-developed head. The foot is also specialized for digging. Nearly all bivalves use gills not only for breathing but also for filtering food particles suspended in the water. The bivalves that burrow in the mud or sand such as clams have two tubes (siphons); one conveys water and food to the mantle and the other conveys waste CHAPTER 6 ENVIRONMENT 141

144 CHAPTER 6 ENVIRONMENT out of the body. Reproduction is sexual. Cephalopods are exclusively marine animals and include squid, octopus and cuttlefish. In these organisms the foot merges with the head and is surrounded by a ring of tentacles eight in octopuses (Octopods) and 10 in cuttlefish and squids (Decapods). Both use well-developed suckers to capture and hold prey. Except for the Nautilus, the shell is internal and tends to be small, but is not present at all in octopus (though it does have a hard beak ). By contracting and releasing muscles through a siphon (funnel) in the mantle, cephalopods can move quickly by a form of water-jet propulsion. These highly-evolved animals - the most intelligent of all vertebrates studied - have a complex nervous and sensory system and a brain capable of learning. Their reproduction is sexual, but well-developed individuals emerge from fertilized egg clusters rather than larvae. Crustaceans Crustaceans are a subphylum of the phylum Arthropoda, the largest and most diverse group of animals on earth. Their unequalled success is due largely to the presence of a rigid external skeleton (exoskeleton), powerful articulated claws and appendages, specialized respiratory system, efficient nervous system and sensory organs, and life cycle. The exoskeleton is a sturdy cuticle made up of proteins and chitin (a polysaccharide), making it light and flexible. It s also strengthened by minerals such as calcium carbonate and calcium phosphate. The disadvantage to this suit of armor is that, once formed, it cannot grow. Instead, crustaceans discard or molt their shells periodically. At each successful molting, they increase in size. 142

145 The head and thorax of crustaceans are merged into what is called the cephalothorax, which precedes the abdomen. Both main parts have articulated appendages specialized in various functions (antennas to sense motion and Sea Star chemicals, claws to grip, limbs to walk or swim, filaments to carry eggs, etc.). Crustaceans include about 40,000 species, nearly all aquatic and mainly marine. They are divided into nine classes, the anus best known of which is the subclass Malacostraca, which comprises the Decapods (having 10 limbs), The sexes are separate, but there are also cases of hermaphroditism. Larvae emerge from fertilized eggs Sea Urchin mouth and undergo several stages of development (metamorphosis) before assuming the adult form. Bryozoans Bryozoans, sometimes called moss animals, belong to a phylum that is not very numerous, though all are aquatic. These are small animals comprising a crown of tentacles set in a horseshoe arrangement around the mouth. They live in colonies that are often calcified, and have a branching tree-like structure. They are hermaphroditic and may reproduce both sexually and asexually. They are of interest to divers for their rigid structures that look like coral. In fact, there is one species, Myriapora truncata, which is incorrectly called a false coral because it s so easily mistaken for precious red coral. anus mouth mouth Brittle star anus no anus mouth anus Sea Lily Asteroidea (sea star) Ophiuridea (Brittle star) mouth Sea Cucumber Echinoidea (Sea Urchin) Crinoidea (sea lily) Holothuria (sea cucumber) CHAPTER 6 ENVIRONMENT 143

146 CHAPTER 6 ENVIRONMENT Echinoderms Another important marine phylum is Echinodermata (which literally means hedgehog skin ). This group includes an extensive array of marine invertebrates such as sea cucumbers, sea urchins and sea stars. There are over 6,000 known species divided into six classes (one, Centricocycloids, is represented by a single species not discovered until in 1986). The other classes are Asteroidea (sea stars), Ophiuroidea (basket or brittle stars), Crinoidea (sea lilies), Echinoidea (sea urchins) and Holothuroidea (sea cucumbers). A common feature in these animals is the presence of spines often modified into rounded tubercles. All have a calcareous skeleton and five-sided or pentameral symmetry clearly visible in the adults (like the five arms of sea stars). A characteristic of echinoderms is the presence of a special system of ducts connected to numerous muscular appendages termed tube feet. These tube feet have suckers activated by varying internal pressure. This enables many species to manipulate prey or adhere to the substrate, move or remain in place. Reproduction is generally sexual, but there are cases of asexual reproduction by fission-regeneration (under certain circumstances sea stars can regenerate lost limbs or a whole animal from a segment of a limb). Chordates The chordates include a vast and varied group of animals (about 47,000 species) including both invertebrates, such as sea squirts, and vertebrates, such as fish and humans. All share four common characteristics, at least in one phase of their life cycle, with two being of particular importance: 1) The presence of a central notochord (from which the name chordate derives). This structure performs a supporting function, and runs along the length of the organism. 2) A tubular dorsal nerve cord, set on top of the notochord. There are many taxa within the phylum Chordata. Of particular interest to divers are the subphylum Urochordata (tunicates), subphylum Vertebrata (animals with backbones). 144

147 Tunicates Urochordates are the tunicates, a group where the notochord is present only in the larval stage (similar in appearance to tadpoles) but disappears as an adult. They are exclusively marine and are divided into three classes: Larvacea, Thaliacea and Ascidiacea. Their body is wrapped in a hard or gelatinous covering called the tunic, made up of a substance similar to cellulose. In adults, the pharynx transforms into an organ with a dual function: respiration and nutrition. Tunicates are mainly hermaphroditic, but some may reproduce asexually. The most common tunicates are ascidians, more commonly known as sea squirts. They have two openings (siphons) through which they filter water to extract oxygen and food. Some ascidians occur as individuals while others form colonies. Also quite common in open water are planktonic tunicates known as salps, which form translucent linked chains of individuals. Vertebrates In vertebrates, the notochord forms a succession of hardened structures called the vertebral column or backbone. This and the rest of the internal skeleton (endoskeleton) are made of either cartilage or bone. There are about 45,000 known species within the superphylum Vertebrata, and of interest to divers are the subclass Agnatha (jawless fish), subclass Osteichthyes (bony fish), and class Chondrichthyes (cartilagenous fish). The other extant (living) classes are the Amphibia (amphibians), Reptilia (reptiles), Aves (birds) and Mammalia (mammals), many of which have marine representatives. CHAPTER 6 ENVIRONMENT 145

148 CHAPTER 6 ENVIRONMENT Fish Agnatha include lampreys and hagfish, which have a cylindrical body and cartilaginous skeleton. Lacking jaws, they have an oral disc similar to a sucker, with horny plates that burrow into their prey. The Chondrichthyes (sharks, skates and rays) have a skeleton made of cartilage rather than bone, with teeth that are modified scales. They are also distinguished by skin covered with tiny tooth-like placoid scales (the rough texture it makes it feel like sandpaper). Most have five gill openings on each side that lack a protective cover (operculum). In rays and skates, which typically live on the sea bottom, the gills are in direct contact with the sediment. This does not hinder respiration as water can reach the gills unobstructed through an opening (spiracle) on the animal s back. In sharks the caudal fin (tail) is typically asymmetrical, with the upper lobe more developed than the lower lobe. The sexes are separate and fertilization is always internal. Reproduction is mainly viviparous (live birth), but several small sharks, such as the dogfishes, and rays reproduce by laying eggs. The Osteichthyes or bony fishes account for most species (nearly 30,000). They differ from the chondrichthyes not only in the composition of their skeleton, but also in their skin that s covered with either smooth-edged cycloid scales or serrated-edged ctenoid scales. Their fins are supported by bony rays that may be rigid or flexible, and they have gills protected by a bony cover (operculum). The sexes can be separate or hermaphroditic. Fertilization is most often external. Reptiles Most marine reptiles are represented by turtles and sea snakes. Turtles have a bony shell divided into a carapace or shield (the top part) and plastron (the bottom part), and limbs well suited to swimming. Tur- 146

149 tles have separate sexes, even though they are difficult to distinguish, and are oviparous (egg-layers). The females periodically return to nesting beaches where they lay their eggs in unattended burrows. Sea snakes occur only in the Indo-Pacific. They differ from their land-based cousins mainly in their tail, which is flattened to aid its movement in water. Most species are ovoviviparous meaning their young are born alive in the sea from internally-hatched eggs but a few species do return to land to lay eggs. Other marine reptiles include the marine iguana, an exclusive resident of the Galapagos Islands, and the marine crocodile commonly found from India to the Solomon Islands. Mammals Marine mammals are too well known not to at least mention. These include the orders Cetacea (dolphins and whales), Sirenia (manatees and sea cows), Carnivora (sea otters and polar bears) and suborder Pinnipedia (seals and sea lions). TROPICAL ENVIRONMENTS While you can dive anywhere water is deep enough to submerge, most diving takes place in the tropics on coral reefs. This should not come as a surprise, given that the water there is warm and clear, and coral reefs abound with more species of marine life than in any other marine habitat. Although coral reefs are the most popular marine habitat among divers, they comprise a very small portion of the sea bottom, less than 0.1% of the ocean s surface or about 100,000 square miles (250,000 square kilometers). That s merely the size of the US State of Colorado or about half the size of France. In some places like Florida, Bermuda and Okinawa, coral reefs exist outside the tropics because ocean currents bring warm water into these regions. Finally, corals require clear water, and this brings us to one of the most important factors in understanding the function of these amazing animals. While corals are animals (Cnidarians), they also CHAPTER 6 ENVIRONMENT 147

150 CHAPTER 6 ENVIRONMENT secrete limestone (calcium carbonate) and could not exist without a close association (symbiosis) with resident single-cell algae collectively termed zooxanthellae. The photosynthetic zooxanthellae provide much of the food the coral polyps need. In turn, the polyps provide a safe place for the zooxanthellae to live. The polyp also provides the raw materials needed by the zooxanthellae in the form of respired carbon dioxide to make sugars and metabolic waste for nutrients (essentially, fertilizer ). Most vitally, as the zooxanthellae carry on photosynthesis, they must have access to light. This is why coral reefs require clear water, and why they re limited to relatively shallow depths. The zooxanthellae provide most of the coral s color, too. When they are lost most coral turn pale or white ( bleach ) as the now transparent skin reveals the colorless limestone beneath the living tissue. Their ability to secrete massive limestone structure give coral reefs a geologic function. Therefore, different types of reefs have different characteristics based on their origin, structure and proximity to the shoreline. Charles Darwin first described coral reefs as fringing reefs (occurring near the shoreline), barrier reefs (separated some distance for the shore) and atolls (circular reefs with no obvious nearby island or mainland). Regardless how large the reef, all are formed by millions upon millions of tiny polyps each secreting its own limestone house called a corallite. Each species secretes a unique form of corallite from which you can determine the species. Only the thin outer veneer of the reef is alive with polyps, and all colony members are connected with a common 148

151 tissue called the coenosarc. All coral reefs begin as a larvae settling on a hard substrate. This larvae secretes limestone becoming the founding polyp. From there it asexually divides, making countless copies of itself and building the reef in the process. When one polyp dies, another simply builds on top of the decedent. The irony is that these enormous structure that can last for millennia are formed by such tiny delicate creatures that can be crushed by the touch of a hand. This is why diving around coral reefs requires good buoyancy control and other responsible diving practices you ll learn from your instructor and dive operator. In general, for your safety and the health of the reef, look but do not touch. Leave only bubbles and take only memories. Reef Zones Although it can vary with location, coral reefs are traditionally divided into three zones: the back reef, reef crest and fore reef. All are subjected to different conditions. The back reef is closest to shore and therefore subject to very difficult conditions. The shallow water means that water temperatures can vary considerably over the day, and whatever sediment or pollutants enter the nearshore waters first affect this community. This means that relatively few but hardy coral species are normally found here. The reef crest, which sometimes reaches all the way to the surface, takes the full brunt of wave energy. Here you often find branching species that allow energy to quickly dissipate through them. Stinging fire coral may also be present. During very low tides the corals in the shallowest water may even have to contend with emersion for a few hours. (They do so by secreting lots of mucus.) Sometimes the wave CHAPTER 6 ENVIRONMENT 149

152 CHAPTER 6 ENVIRONMENT energy is so strong that only coralline algae can live here, forming a dull, featureless ridge. In less energetic environments the crest may contain diversity of both corals, fishes and other invertebrates taking advantage of the planktonic food brought to them by the wave action. The fore reef is sometimes known as the drop off, especially when it falls away almost vertically into the abyss. With less disturbance from waves more species can survive until depths are reached where light diminishes to a point where the zooxanthellae can no longer do their job of feeding their host polyps. Below this depth exist a few corals that do not host zooxanthellae, along with sponges and, of course, fishes. The high energy environment of the outer reef, and the many bioeroding (boring) organisms that reside there, can also give rise to spectacular canyon-like formations called spurs and grooves as well as extensive caves and caverns. The fore reef is usually the zone divers most enjoy. A glance at reef life Reefs are fascinating, complex environments that are hard to describe in brief. Now that you know a bit about the essential characteristics of coral reefs, let s look closer at other aspects of life on the reef. While the reef world may seem chaotic, it is anything but; there are clear reasons why everything you observe happens in the way it does. Perhaps the most important rule for life on the reef is to eat without being eaten; and the rule applies to all residents, including the corals. It may not look like it, but all corals are equipped with fearsome weapons. Like all Cnidarians, they have stinging cells (cnidocyte) distributed throughout their tentacles. Most corals can only 150

153 sting and capture tiny zooplankton, but some, like fire coral, have cnidocytes powerful enough to inflict a painful sting on humans (another good reason not to touch anything when reef diving). Soft corals defend themselves by depositing sharp calcareous spicules within their tissues to discourage predators. Sponges take a similar approach, as well as employing power toxins. Another sign of toxicity is garish coloration, a warning mechanism employed by nudibranchs (though some fishes are immune to these toxins). Molluscs and crustaceans use yet a different strategy, using strong shells for defense against predators or elaborate camouflage enabling them to hide discretely within the reef. Even the bright colors of many fishes are, in reality, a means of defense. For example, the bright black spots decorating the posterior of many butterfly fish are, in reality, fake eyes that fool predators. The distinct stripes seen on many fish swimming among the corals actually break up their outline, acting as camouflage in the same way as the black and white stripes of zebras or the stripes of tigers do in their native background. You can also learn a lot by studying the shape and structure of an organism, or what s called its morphology. For sessile (attached) creatures like coral and anemones a circular body plan is useful as it allows them to collect food from any direction, while some echinoderms like brittle sea stars and crinoids have scores of feathered arms. Studying their morphology is also an excellent way of understanding fish. Obviously, the shape of a moray eel allows it to swim effortlessly through cracks and crevasses in the reef, while coralivorous butterfly fish, with their high, flat bodies, move easily through coral colonies to access their favorite food, polyps. Using camouflage or by partially burying themselves in sediment, many CHAPTER 6 ENVIRONMENT 151

154 CHAPTER 6 ENVIRONMENT bottom-dwelling fish lay in wait to ambush their prey. Other predators, like barracuda, use speed and efficient hydrodynamic shape to swiftly chase down their slower swimming meal. Specialization extends even to the way some fish eat. The shape and capability of fishes mouths can be very revealing. Jaw construction allows some fish to selectively pick food from the water, while others have jaws and teeth that allow them to crush invertebrates picked from the sediment or coral colony. In the case of the herbivorous parrotfish, their specialized teeth allow them to bite and scrape the limestone reef to harvest algae. Studying fish morphology also gives insight into defensive strategies. Some slow moving reef fish avoid being eaten by possessing bony plates under their skin or by erecting spines that make them an unwise choice as a meal. The social relations between fish are also extremely varied. Some are territorial species like damselfishes and clown fish, as well as many wrasses and groupers, while some fish simply wander the reef in search of food or mates. Others move in schools to provide safety in numbers, and to improve their chance of finding food. Coral reefs are somewhat like factories that never close. Once the sun goes down, the day shift goes home and the night shift takes over. If you dive at night you ll discover a world that is completely different from the day. Many conspicuous daytime fish, like parrotfish and wrasses, disappear among the corals or bury themselves under the sand. Butterflyfish and angelfish also disappear, and are replaced by red soldierfish and squirrelfish which, during the day, occupy caves and dark crevasses. Some nocturnal types such 152

155 as moray eels, bigeyes and cardinal fish are busy hunting other fish, plankton, or invertebrates. Others, like grunts, are also busy hunting, but leave the sanctuary of the reef to stalk nearby seagrass beds. The world of the invertebrates also changes at night. Each night tiny planktonic creatures ascend from the safety of their hiding places within the reef into the water column to hunt even smaller prey. Coral polyps extend their hungry tentacles in hope of capturing some of this planktonic meal if it swims too close. Herbivorous sea urchins also take advantage of their absent predators and actively feed on algae. Many gastropods roam the bottom scouring up organic material from the sediment, while some actively hunt for prey using poisonous darts that they shoot with great precision. Even the sandy bottom, of little interest during the day, comes alive with hunters such as stingrays, gobies, and crocodile fish. Surely, the reef is just as beautiful - and deadly - at night as it is in daylight. SUMMARY Congratulations! You ve reached the end of the course. Aside from the skills and techniques needed to dive safety you now also have some insight into the workings of the underwater world. Never forget that, when visiting this world, you are a guest and you must always leave it no worse off than you found it. You are now ready to embark on the adventure of a lifetime where you can discover not only what s under water but above as well. Diving can be a ticket to discover new countries and different cultures, and socialize with others who share the same passion. However, remember that you re only beginning a journey; your education should not stop here. By continuing your training with SNSI, you ll gain the experience and confidence to feel completely ease in any underwater environment you wish to experience. The adventure starts now, so DiveUpYourLife! Watch the SNSI OWD Scuba Skills #4 Video CHAPTER 6 ENVIRONMENT 153

156 STUDY GUIDE: CHAPTER 6 CHAPTER 6 ENVIRONMENT 1. Water will absorb heat from you about times faster than air Waives are caused by the wind blowing on the surface of the Water. True. False. 3. Currents are caused by many factors including bottom topography and tides. True. False. 154

157 APPENDIX: DIVE TABLES U.S. NAVY DIVING TABLE Table 9-9. Air Decompression Table. (DESCENT RATE 75 FPM ASCENT RATE 30 FPM) Bottom Time (min) 30 FSW Time to First Stop (M:S) Gas Mix DECOMPRESSION STOPS (FSW) Stop times (min) include travel time, except first air and first O 2 stop Total Ascent Time (M:S) Chamber O 2 Periods 371 1:00 AIR 0 1:00 0 Z AIR/O 2 0 1: :20 AIR 5 6: Z AIR/O 2 1 2:00 In-Water Air/O 2 Decompression or SurDO 2 Recommended :20 AIR 22 23: Z AIR/O 2 5 6: :20 AIR 42 43: AIR/O : :20 AIR 71 72:00 1 AIR/O :00 Exceptional Exposure: In-Water Air Decompression In-Water Air/O 2 Decompression or SurDO 2 Required :20 AIR 92 93:00 1 AIR/O : :20 AIR :00 1 AIR/O : :20 AIR : FSW AIR/O : :10 AIR 0 1:10 0 Z AIR/O 2 0 1: :30 AIR 4 5: Z AIR/O 2 2 3:10 In-Water Air/O 2 Decompression or SurDO 2 Recommended :30 AIR 28 29: Z AIR/O 2 7 8: :30 AIR 53 54: Z AIR/O : :30 AIR 71 72:10 1 Z AIR/O : :30 AIR 88 89:10 1 AIR/O :10 Exceptional Exposure: In-Water Air Decompression In-Water Air/O 2 Decompression or SurDO 2 Required :30 AIR : AIR/O : :30 AIR : AIR/O : :30 AIR :10 2 AIR/O : :30 AIR :10 2 AIR/O : :30 AIR : AIR/O : :30 AIR :10 3 AIR/O :10 Repet Group 155

158 APPENDIX: DIVE TABLES U.S. NAVY DIVING TABLE Table 9-9. Air Decompression Table (Continued). (DESCENT RATE 75 FPM ASCENT RATE 30 FPM) Bottom Time (min) 40 FSW Time to First Stop (M:S) Gas Mix DECOMPRESSION STOPS (FSW) Stop times (min) include travel time, except first air and first O 2 stop Total Ascent Time (M:S) Chamber O 2 Periods 163 1:20 AIR 0 1:20 0 O AIR/O 2 0 1: :40 AIR 6 7: O AIR/O 2 2 3: :40 AIR 14 15: Z AIR/O 2 5 6:20 In-Water Air/O 2 Decompression or SurDO 2 Recommended :40 AIR 21 22: Z AIR/O 2 7 8: :40 AIR 27 28: Z AIR/O : :40 AIR 39 40: Z AIR/O : :40 AIR 52 53: Z AIR/O : :40 AIR 64 65:20 1 Z AIR/O : :40 AIR 75 76:20 1 Z AIR/O :20 Exceptional Exposure: In-Water Air Decompression In-Water Air/O 2 Decompression or SurDO 2 Required :40 AIR :20 1 Z AIR/O : :40 AIR : AIR/O : :40 AIR : AIR/O : :40 AIR :20 2 AIR/O : :40 AIR : AIR/O : :40 AIR : AIR/O :20 Exceptional Exposure: In-Water Air/0 2 Decompression SurDO 2 Required :40 AIR :20 3 AIR/O : :40 AIR : AIR/O : :40 AIR :20 4 AIR/O :20 Exceptional Exposure: SurDO :40 AIR : AIR/O :20 Repet Group 156

159 APPENDIX: DIVE TABLES U.S. NAVY DIVING TABLE Table 9-9. Air Decompression Table (Continued). (DESCENT RATE 75 FPM ASCENT RATE 30 FPM) Bottom Time (min) 45 FSW Time to First Stop (M:S) Gas Mix DECOMPRESSION STOPS (FSW) Stop times (min) include travel time, except first air and first O 2 stop Total Ascent Time (M:S) Chamber O 2 Periods 125 1:30 AIR 0 1:30 0 N AIR/O 2 0 1: :50 AIR 2 3: O AIR/O 2 1 2: :50 AIR 14 15: O AIR/O 2 5 6:30 In-Water Air/O 2 Decompression or SurDO 2 Recommended :50 AIR 25 26: Z AIR/O 2 8 9: :50 AIR 34 35: Z AIR/O : :50 AIR 41 42:30 1 Z AIR/O : :50 AIR 59 60:30 1 Z AIR/O : :50 AIR 75 76:30 1 Z AIR/O :30 Exceptional Exposure: In-Water Air Decompression In-Water Air/O 2 Decompression or SurDO 2 Required :50 AIR 89 90:30 1 Z AIR/O : :50 AIR :30 1 Z AIR/O : :50 AIR : Z AIR/O : :50 AIR : Z AIR/O : :50 AIR : Z AIR/O : :50 AIR :30 2 AIR/O : :50 AIR :30 2 AIR/O : :50 AIR : AIR/O : :50 AIR :30 3 AIR/O :30 Exceptional Exposure: In-Water Air/0 2 Decompression SurDO 2 Required :50 AIR : AIR/O : :50 AIR :30 4 AIR/O :30 Exceptional Exposure: SurDO :50 AIR : AIR/O :30 Repet Group 157

160 APPENDIX: DIVE TABLES U.S. NAVY DIVING TABLE Table 9-9. Air Decompression Table (Continued). (DESCENT RATE 75 FPM ASCENT RATE 30 FPM) Bottom Time (min) Time to First Stop (M:S) Gas Mix DECOMPRESSION STOPS (FSW) Stop times (min) include travel time, except first air and first O 2 stop Total Ascent Time (M:S) Chamber O 2 Periods 50 FSW 92 1:40 AIR 0 1:40 0 M AIR/O 2 0 1: :00 AIR 2 3: M AIR/O 2 1 2: :00 AIR 4 5: N AIR/O 2 2 3: :00 AIR 8 9: O AIR/O 2 4 5:40 In-Water Air/O 2 Decompression or SurDO 2 Recommended :00 AIR 21 22: O AIR/O 2 7 8: :00 AIR 34 35: Z AIR/O : :00 AIR 45 46:40 1 Z AIR/O : :00 AIR 56 57:40 1 Z AIR/O : :00 AIR 78 79:40 1 Z AIR/O :40 Exceptional Exposure: In-Water Air Decompression In-Water Air/O 2 Decompression or SurDO 2 Required :00 AIR 96 97:40 1 Z AIR/O : :00 AIR : Z AIR/O : :00 AIR : Z AIR/O : :00 AIR : Z AIR/O : :00 AIR :40 2 AIR/O : :00 AIR :40 2 AIR/O : :00 AIR :40 2 AIR/O : :00 AIR :40 2 AIR/O : :00 AIR : AIR/O : :00 AIR :40 3 AIR/O :40 Exceptional Exposure: In-Water Air/O 2 Decompression SurDO 2 Required :00 AIR : AIR/O : :00 AIR : AIR/O :40 Exceptional Exposure: SurDO :00 AIR : AIR/O :40 Repet Group 158

161 APPENDIX: DIVE TABLES U.S. NAVY DIVING TABLE Table 9-9. Air Decompression Table (Continued). (DESCENT RATE 75 FPM ASCENT RATE 30 FPM) Bottom Time (min) Time to First Stop (M:S) Gas Mix DECOMPRESSION STOPS (FSW) Stop times (min) include travel time, except first air and first O 2 stop Total Ascent Time (M:S) Chamber O 2 Periods 55 FSW 74 1:50 AIR 0 1:50 0 L AIR/O 2 0 1: :10 AIR 1 2: L AIR/O 2 1 2: :10 AIR 4 5: M AIR/O 2 2 3: :10 AIR 10 11: N AIR/O 2 5 6:50 In-Water Air/O 2 Decompression or SurDO 2 Recommended :10 AIR 17 18: O AIR/O 2 8 9: :10 AIR 34 35: O AIR/O : :10 AIR 48 49:50 1 Z AIR/O : :10 AIR 59 60:50 1 Z AIR/O : :10 AIR 84 85:50 1 Z AIR/O :50 Exceptional Exposure: In-Water Air Decompression In-Water Air/O 2 Decompression or SurDO 2 Required :10 AIR : Z AIR/O : :10 AIR : Z AIR/O : :10 AIR : Z AIR/O : :10 AIR :50 2 Z AIR/O : :10 AIR :50 2 AIR/O : :10 AIR :50 2 AIR/O : :10 AIR : AIR/O : :10 AIR : AIR/O : :10 AIR : AIR/O : :10 AIR :50 3 AIR/O :50 Exceptional Exposure: In-Water Air/0 2 Decompression SurDO 2 Required :10 AIR : AIR/O : :10 AIR : AIR/O : :10 AIR :50 4 AIR/O :50 Exceptional Exposure: SurDO :10 AIR : AIR/O :50 Repet Group 159

162 APPENDIX: DIVE TABLES U.S. NAVY DIVING TABLE Table 9-9. Air Decompression Table (Continued). (DESCENT RATE 75 FPM ASCENT RATE 30 FPM) Bottom Time (min) Time to First Stop (M:S) Gas Mix DECOMPRESSION STOPS (FSW) Stop times (min) include travel time, except first air and first O 2 stop Total Ascent Time (M:S) Chamber O 2 Periods 60 FSW 60 2:00 AIR 0 2:00 0 K AIR/O 2 0 2: :20 AIR 2 4: L AIR/O 2 1 3: :20 AIR 7 9: L AIR/O 2 4 6: :20 AIR 14 16: N AIR/O 2 7 9:00 In-Water Air/O 2 Decompression or SurDO 2 Recommended :20 AIR 23 25: O AIR/O : :20 AIR 42 44:00 1 Z AIR/O : :20 AIR 57 59:00 1 Z AIR/O : :20 AIR 75 77:00 1 Z AIR/O :00 Exceptional Exposure: In-Water Air Decompression In-Water Air/O 2 Decompression or SurDO 2 Required :20 AIR : Z AIR/O : :20 AIR : Z AIR/O : :20 AIR :00 2 Z AIR/O : :20 AIR :00 2 Z AIR/O : :20 AIR :00 2 AIR/O : :20 AIR : AIR/O : :20 AIR : AIR/O : :20 AIR : AIR/O : :20 AIR :00 3 AIR/O : :20 AIR :00 3 AIR/O :00 Exceptional Exposure: In-Water Air/0 2 Decompression SurDO 2 Required :20 AIR : AIR/O : :20 AIR : AIR/O : :20 AIR :00 4 AIR/O :00 Exceptional Exposure: SurDO :20 AIR : AIR/O :00 Repet Group 160

163 APPENDIX: DIVE TABLES TABLE 1 SNSI DIVE TABLES BASED ON U.S. NAVY (Rev.6 April 2008) AND NOAA DIVE TABLES DOPPLER NO-DECOMPRESSION LIMITS TABLE: Find the planned mixture and the depth of your dive at the far left of Table. Read to the right until you find the time (minutes) you plan to stay at the depth. Read upwards to find the Repetitive Group Designation letter. DEPTH NDL REPETITIVE GROUP DESIGNATION ARIA 3 4,5 6 7,5 9 10, TABLE 2 EAN 32 EAN 36 Doppler U.S. Navy NOAA 4, No Limit 6 7,5 217 No Limit 7, No Limit 9 10, SURFACE INTERVAL TABLE: Enter with the Repetitive Group Designation from table. Follow the arrow to the corresponding letter on Table 2. Read to the left until you find the times between witch your surface interval falls. Then read down until you find your new Repetitive Group Designation. (*) Dives following surface intervals longer than this are not repetitive dives. 0:10 2:20* 1:17 3:36* 2:12 4:31* 3:04 5:23* 3:56 6:15* 4:49 7:08* A B C D E F G H I J K L 0:10 1:16 0:56 2:11 1:48 3:03 2:40 3:55 3:32 4: A B C D E F G H I J K L :10 0:55 0:53 1:47 1:45 2:39 2:38 3:31 0:10 0:52 0:53 1:44 1:45 2:37 0:10 0:52 0:53 1:44 0:10 0:52 5:41 8:00* 4:24 5:40 3:30 4:23 2:38 3:29 1:45 2:37 0:53 1:44 0:10 0:52 6:33 8:52* 5:17 6:32 4:22 5:16 3:30 4:21 2:38 3:29 1:45 2:37 0:53 1:44 0:10 0:52 7:25 9:44* 6:09 7:24 5:14 6:08 4:22 5:13 3:30 4:21 2:38 3:29 1:45 2:37 0:53 1:44 0:10 0: :36* 7:01 8:16 6:07 7:00 5:14 6:06 4:22 5:13 3:30 4:21 2:38 3:29 1:45 2:37 0:53 1:44 0:10 0:52 TABLE 3 RESIDUAL NITROGEN TIME TABLE: Enter with the new ARIA EAN 32 EAN 36 Repetitive Group Designation from 3 4,5 6 table 2. Next, find the planned mixture and 6 7,5 9 depth of your repetitive dive in meters at the far left of Table 3. The box that intersects the Repetitive dive depth and the new Repetitive Group Designation letter will have two numbers. The top number (yellow box) indicates the Residual Nitrogen time in minutes. The bottom number (green box) indicated the maximum adjusted No-Decompression time limit, in minutes, for the next dive :10 11:29* 10:02 12:21* A B C D E F G H I J K L Residual Nitrogen Time Adjusted No-Decompression Time Limits Max No-Decompression time limits U.S. Navy/NOAA Tables :53 9:09 8:45 10:01 6:59 7:52 7:51 8:44 6:07 6:58 6:59 7:50 5:14 6:06 6:07 6:58 4:22 5:13 5:14 6: :30 4:21 4:22 5:13 2:38 3:29 3:30 4: :45 2:37 2:38 3: :53 1:44 1:45 2: :10 0:52 0:53 1: :10 0: SCUBA AND NITROX SAFETY INTERNATIONAL 161

164 APPENDIX: DIVE TABLES CNS% AND UPTD TABLE RELATIVE TO OXYGEN PARTIAL PRESSURE OXYGEN PARTIAL PRESSURE TABLE AT VARIOUS DEPTHS P02 CNS% UPTD bar per min. per min. Exposure limit (min.) in 24 hours DEPTH AIR EAN 32 EAN 36 0,8 0,9 1,0 1,1 1,2 1,3 1,4 1,5 1,6 0,22% 0,28% 0,33% 0,42% 0,47% 0,56% 0,65% 0,83% 2,22% 0,65 0,93 1,00 1,16 1,32 1,48 1,63 1,78 1,93 SNSI RULES REGARDING THE OXYGEN ATTENTION FACTOR MAX 0 2 PARTIAL PRESSURE = 1,5 BAR MAXIMUM TIME LIMITS: 120 MINUTES FOR SINGLE DIVE 180 MINUTES (TOTAL) FOR REPETITIVE DIVES Single Ripetitive 1 - The maximum bottom time for each single nitrox dive will be 120 minutes regardless of the depth reached and the mixture used. 2 - For repetitive dives, the maximum bottom time may not exceed 180 minutes in 24 hours. 3 - The above named points apply only by adhering to the maximum depth allowed for EAN32 and EAN36 mixtures (36 meters and 30 metes respectively). 4 - The surface interval between two nitrox dives regardless of the planned parameters may not be less than 2 hours (120 minutes). 5 - In case of reaching the maximum time limit allowed during repetitive nitrox dives then it must be done 12 hours surface interval prior to make another dive regardless of residual nitrogen values. 6 - It is highly recommended to make only 2 nitrox dives per day. In case of a third dive, then it must be conducted in air to a maximum depth of 15 meters. 7 - Care must be taken always not to mistake the no-decompression time limits with that of exposure to higher oxygen partial pressure. 8 - Abnormal or suspicious CO 2 increased conditions (fatigue, cold or stress) must be used as a sign to reduce up to half the intended dive parameters and if the problem persists the dive must be interrupted ,27 6 0,33 9 0, , , , , , , , , ,03 Meters Pp0 2 4,5 0,46 7,5 0, , , , , , , , , ,57 6 0,58 9 0, , , , , , , ,55 SCUBA AND NITROX SAFETY INTERNATIONAL WARNING: The U.S. Navy e NOAA dive tables are designed to Navy specifications for use by Navy Divers. When used by recreational divers, the tables should be used conservatively. Even when used correctly with proper safety procedures, decompression sickness may still occur. SAFETY STOP PROCEDURE: It is recommended to make a 2-5 minutes safety stop at 5 meters an all dives in Nitrox or Air deeper than 9 mters.. OMITTED DECOMPRESSION PROCEDURE: Should you exceed the Doppler No-Decompression time limits by less than 5 minutes, it is recommended that you ascend normally to 5 meters and stop for at least 10 minutes or longer if you air supply allows. Should you exceed the Doppler No-Decompression time limits by more than 5 minutes but less than 10 minutes, it is recommended that you ascend normally to 5 meters and stop for at least 20 minutes or longer if you air supply allows. Refrain from any further Scuba Diving activities for at least 24 hours 162

165 APPENDIX: DIVE TABLES TABLE 1 SNSI DIVE TABLES BASED ON U.S. NAVY (Rev.6 April 2008) AND NOAA DIVE TABLES DOPPLER NO-DECOMPRESSION LIMITS TABLE: Find the planned mixture and the depth of your dive at the far left of Table. Read to the right until you find the time (minutes) you plan to stay at the depth. Read upwards to find the Repetitive Group Designation letter. DEPTH (fsw) NDL REPETITIVE GROUP DESIGNATION AIR TABLE 2 EAN 32 EAN 36 Doppler U.S. Navy NOAA No Limit No Limit No Limit SURFACE INTERVAL TABLE: Enter with the Repetitive Group Designation from table. Follow the arrow to the corresponding letter on Table 2. Read to the left until you find the times between witch your surface interval falls. Then read down until you find your new Repetitive Group Designation. (*) Dives following surface intervals longer than this are not repetitive dives. 0:10 2:20* 1:17 3:36* 2:12 4:31* 3:04 5:23* 3:56 6:15* 4:49 7:08* A B C D E F G H I J K L 0:10 1:16 0:56 2:11 1:48 3:03 2:40 3:55 3:32 4: A B C D E F G H I J K L :10 0:55 0:53 1:47 1:45 2:39 2:38 3:31 0:10 0:52 0:53 1:44 1:45 2:37 0:10 0:52 0:53 1:44 0:10 0:52 5:41 8:00* 4:24 5:40 3:30 4:23 2:38 3:29 1:45 2:37 0:53 1:44 0:10 0:52 6:33 8:52* 5:17 6:32 4:22 5:16 3:30 4:21 2:38 3:29 1:45 2:37 0:53 1:44 0:10 0:52 7:25 9:44* 6:09 7:24 5:14 6:08 4:22 5:13 3:30 4:21 2:38 3:29 1:45 2:37 0:53 1:44 0:10 0: :36* 7:01 8:16 6:07 7:00 5:14 6:06 4:22 5:13 3:30 4:21 2:38 3:29 1:45 2:37 0:53 1:44 0:10 0:52 TABLE 3 RESIDUAL NITROGEN TIME TABLE: Enter with the new AIR EAN 32 EAN 36 Repetitive Group Designation from table 2. Next, find the planned mixture and depth of your repetitive dive in feet at the far left of Table 3. The box that intersects the Repetitive dive depth and the new Repetitive Group Designation letter will have two numbers. The top number (yellow box) indicates the Residual Nitrogen time in minutes. The bottom number (green box) indicated the maximum adjusted No-Decompression time limit, in minutes, for the next dive :10 11:29* 10:02 12:21* A B C D E F G H I J K L Residual Nitrogen Time Adjusted No-Decompression Time Limits Max No-Decompression time limits U.S. Navy/NOAA Tables :53 9:09 8:45 10:01 6:59 7:52 7:51 8:44 6:07 6:58 6:59 7:50 5:14 6:06 6:07 6:58 4:22 5:13 5:14 6: :30 4:21 4:22 5:13 2:38 3:29 3:30 4: :45 2:37 2:38 3: :53 1:44 1:45 2: :10 0:52 0:53 1: :10 0: SCUBA AND NITROX SAFETY INTERNATIONAL 163

166 APPENDIX: DIVE TABLES CNS% AND UPTD TABLE RELATIVE TO OXYGEN PARTIAL PRESSURE P02 CNS% UPTD ata per min. per min % 0.28% 0.33% 0.42% 0.47% 0.56% 0.65% 0.83% 2.22% SNSI RULES REGARDING THE OXYGEN ATTENTION FACTOR MAX 0 2 PARTIAL PRESSURE = 1.5 ATA (22.0 PSI) MAXIMUM TIME LIMITS: 120 MINUTES FOR SINGLE DIVE 180 MINUTES (TOTAL) FOR REPETITIVE DIVES Exposure limit (min.) in 24 hours Single Ripetitive 1 - The maximum bottom time for each single nitrox dive will be 120 minutes regardless of the depth reached and the mixture used. 2 - For repetitive dives, the maximum bottom time may not exceed 180 minutes in 24 hours. 3 - The above named points apply only by adhering to the maximum depth allowed for EAN32 and EAN36 mixtures (120 feet and 100 feet respectively). 4 - The surface interval between two nitrox dives regardless of the planned parameters may not be less than 2 hours (120 minutes). 5 - In case of reaching the maximum time limit allowed during repetitive nitrox dives then it must be done 12 hours surface interval prior to make another dive regardless of residual nitrogen values. 6 - It is highly recommended to make only 2 nitrox dives per day. In case of a third dive, then it must be conducted in air to a maximum depth of 50 feet. 7 - Care must be taken always not to mistake the no-decompression time limits with that of exposure to higher oxygen partial pressure. 8 - Abnormal or suspicious CO 2 increased conditions (fatigue, cold or stress) must be used as a sign to reduce up to half the intended dive parameters and if the problem persists the dive must be interrupted OXYGEN PARTIAL PRESSURE TABLE AT VARIOUS DEPTHS AIR EAN 32 EAN ata 3.97 psi ata 5.00 psi ata 5.88 psi ata 6.91 psi ata 7.79 psi ata 8.67 psi ata 9.70 psi ata psi ata psi ata psi ata psi ata psi ata psi Depth (fsw) Pp0 2 (ata - psi) ata 6.91 psi ata 8.23 psi ata psi ata psi ata psi ata psi ata psi ata psi ata psi ata psi ata psi ata 8.52 psi ata psi ata psi ata psi ata psi ata psi ata psi ata psi ata psi SCUBA AND NITROX SAFETY INTERNATIONAL WARNING: The U.S. Navy e NOAA dive tables are designed to Navy specifications for use by Navy Divers. When used by recreational divers, the tables should be used conservatively. Even when used correctly with proper safety procedures, decompression sickness may still occur. SAFETY STOP PROCEDURE: It is recommended to make a 2-5 minutes safety stop at 15 feet an all dives in Nitrox or Air deeper than 9 mters.. OMITTED DECOMPRESSION PROCEDURE: Should you exceed the Doppler No-Decompression time limits by less than 5 minutes, it is recommended that you ascend normally to 15 feet and stop for at least 10 minutes or longer if you air supply allows. Should you exceed the Doppler No-Decompression time limits by more than 5 minutes but less than 10 minutes, it is recommended that you ascend normally to 15 feet and stop for at least 20 minutes or longer if you air supply allows. Refrain from any further Scuba Diving activities for at least 24 hours 164

167 Our Objectives: Campaign to study mangroves: the unique tree that grows in salty water. Hippocampus Mission : Census of Mediterranean population of seahorses. Census of Caulerpa taxifolia: An algae that must be monitored continuously because it is harmful to the environment. DIVE WITH US INTO A GREAT GLOBAL PROJECT Code for C-Card application Project Save the Manatees for the protection of these mammals. Project Mediterranean underwater Biodiversity. STE Project: Scuba Tourism for the Environment

168 If you enjoy the outdoors, like adventure, and sports that require physical and mental dexterity This program is for you! You may be reading it for pleasure, curiosity about SCU- BA or to learn more about the SNSI and our Dynamic, Modern Educational System. However, if you are reading it as part of one of the many highly sought after SNSI SCUBA Training Programs, you should be aware that it is only part of the educational system for learning to SCUBA dive safely and enjoyably. There is additional, required in water training with an SNSI Instructor and no book alone can replace the knowledge, experience and safety that only an SNSI instructor will impart. Join us and you will embark on a never ending journey of a lifetime, full of discoveries and adventures with memories you will treasure forever! ISO : Level 2: Autonomous Diver Copyright SNSI All rights reserved.