1. Properties of gases 2. Cylinders 3. Storage of Gases 4. Regulators 5. Cryogenic Liquids Introduction All compressed gases by definition can be hazardous Know the properties of the gases you are working with, meaning you should read your MSDS sheets before using the gases It is important to be aware of not only the chemical hazards associated with the gas, but the hazards associated with the physical properties as well Compressed Gas Properties High Pressure: high inherent potential energy that can be released during a rupture Asphyxiant: gases can displace oxygen and make it difficult to breath Pyrophoric: gases which under normal conditions ignite upon contact with air Cryogenic: gases at very low temperatures that can cause burns or frostbite when in contact with skin Inert Gases: gases that do not react with anything, but they are asphyxiants Flammable : gases that when mixed with an oxidizer in a given range of concentrations can burn Compressed Gas Properties Definition of a Compressed Gas Oxidizing: gases which do not burn, but support and aid combustion Corrosive gases: cause destruction of material or tissue when contact is made, or do so in the presence of moisture Poisonous: produce chemically injurious or lethal effects in humans Any substance contained under pressure Includes dissolved gas or a gas liquified by compression or refrigeration With a critical temperature of less than 50 C Absolute vapour pressure of greater than 275.8kPa @ 21 C or 717 kpa @ 54 C or both or any liquid having an absolute vapour pressure exceeding 275.8 KPa@ 37.8 C
Example: How dangerours is Nitrogen? Nitrogen comprises 78% of our atmosphere, yet it was responsible for 80 deaths between 1992 and 2002 Occurred in laboratories, medical facilities, industrial plants Nitrogen and Helium are such hazards that NMR facilities use Oxygen sensors to ensure that the air is breathable at all times Properties of Cylinders Heavy, smooth, hard to grip Up to 57 inches (~140 cm) tall Can weight up to 150 lbs Have been know to cause injury and even death in some circumstances Physical hazards include tipping, rolling, uncontrolled projectile, bounce, pinning 1. Cylinder Cap 2. Valve Handwheel 3. Valve Outlet Connection 4. Valve Pack Nut 5. Pressure relief valve 6. Valve Outlet Cap 7. Cylinder Collar 8. DOT/Cylinder type & PSI rating 9. Cylinder serial number 10. Initial hydrostatic test date 11. First 5 year hydrostatic retest 12. qualifies for 10 year retest 13. Original inspectors insignia 1. 2. 4. 5. 3. 7. 8. 10. 9. 11. 12. 13. 6. Left-handed (notched fitting) Right-handed handed Standard cylinder outlets have been devised by the Compressed Gas Association (CGA) to prevent mixing of incompatible gases As a result, some fittings have either left or right handed threads, some internal, some external One should never change the adaptor on a regulator to prevent mixing of incompatible gases Cylinder Specifics Labels Always read the labels, never use cylinders that have no identification Always read MSDS sheets prior to use Read your SOP prior to use for specific instructions prior to handling Cylinder colours in no way, shape or form identify their contents, only labels indentify what is contained inside the cylinders
Moving of Cylinders You are required to use a cylinder trolley to move a cylinder over even short distances The trolley must be either a three or four wheeled cart, two wheels are not sufficient Secure the chain around the cylinder before attempting to move and push the cart, not pull it Avoid knocking and rolling the cylinders around and be aware that during transport the cylinders can be unstable Do not transport a cylinder without its cap in place, never move it with a regulator installed Why Do We Secure Cylinders? Cylinders, if they fall over, can become projectiles with such a force that they can smash through brick walls Storage Location of Gases Non flammables may be inside or outside of building Flammables must be outside of building Securing of Gas Cylinders Store in approved cages secured with cap Store away from heat, sunlight, weather Corrosive gases should not be kept for a long period of time Check recommendation of manufacturer Purchase least amount possible, but use common sense Do not order more than you can use, track what you use and adjust your order Gas cylinders must be secured at all times, whether in use or not, empty or full They must be attached to the wall, individually to the wall, or placed in a holding cage Chains or sturdy straps must be used to secure cylinder ¾ of the way up the cylinder
Types of Regulators Two-Stage Low Pressure Single-Stage High Pressure Regulators Delivery Pressure Gauge Flow Control Valve Cylinder Pressure Gauge Cylinder Connection Delivery Pressure Adjustment Knob Be certain that the tubing used to carry the gas from the regulator to its end use is compatible with the gas. Example: Copper tubing + acetylene =copper acetylene (explosive) Fittings for flammable, toxic and air reactive gases need to be checked at each installation on a new cylinder Never use excessive force always use the proper tools When attaching regulator, ensure that it is in the closed position After installation, open valve on cylinder slowly and look to see how much pressure is in the cylinder Notes on Regulators Check the regulator connections for leaks with appropriate leak detections equipment approved for the gas (it is up to the PI to ensure that the cylinder is in good condition and leak tested on a regular basis) Never use teflon tape, solvent or grease on the regulator fittings For corrosive gases, must use teflon o-rings If you feel a cylinder is not in good condition, return it to the supplier Installation of Regulator- Step by Step Setup your cylinder in its location, ensuring that it is secured to the wall or to the bench top with either a chain or a strap If it is a toxic, corrosive or air reactive, be sure to set up in a gas cabinet or fumehood
Remove the cap from the cylinder Select the appropriate regulator for your gas, make sure it has the correct CGA fitting for the cylinder Clean the threads of the cylinder with a brass brush or dry kimwipe, ensure that they are in good shape Inspect the regulator CGA fitting threads to make sure they are also in good shape Make sure that all threads are grease, solvent and teflon tape free Hand tighten the regulator, be certain to not cross thread it or strip it Use a proper wrench to tighten down, do not over tighten (use a proper box wrench as crescent wrenches tend to strip the regulator fitting) Ensure that all valves on the regulator are closed, then stand so that you are not in the path of any objects should they fly off of the regulator and open the cylinder Close the cylinder and wait ten minutes to see if the pressure decreases to test for leaks Check the other seals immediately with an appropriate method to ensure that there are no leaks Closing the Cylinder Turn the delivery pressure adjustment pressure knob clockwise until the desired pressure is reached on the delivery pressure guage Turn counter-clockwise to get lower pressure Close the main valve and bleed the lines if possible Turn the delivery pressure knob counter clockwise Remove the regulator from the cylinder and replace the safety cap If the cylinder is empty, remove to empty cylinder storage Never drain a cylinder completely empty Regulator Maintenance Standard visual checks of the regulators before each use to ensure that there is no visible damage Pressure check and functional test every 6 months Supplier servicing every 2 years Gas which when compressed in a container becomes liquid At ordinary temperature and pressure 25 2500 psig Boiling point range from 130 to 30 F ( 90 to 1 C) @ 70 F (21.1 C) the cylinder contains both liquid and gas
Properties of Liquid Nitrogen 78% of Atmosphere Colorless, Odorless, Tasteless and Nontoxic Boils at -320 degrees Fahrenheit (-196 C) Non-Flammable WILL NOT SUPPORT LIFE Gas is slightly lighter than air Characteristics of Cryogenic Liquid Nitrogen Primary Hazards Asphyxiation Potential for rupture of containers, pipelines, or systems. When liquid or even cold vapor is trapped between valves there is the potential to cause a pressure buildup to a point of violent rupture to a container or piping. (Reliable pressure relief devices are used to prevent this) Example: 1 cubic foot of liquid nitrogen will expand to 696 cubic feet of 100% gaseous nitrogen at 70 F The nitrogen gas can displace the oxygen in the area, leading to asphyxiation This is why cryogenic liquids should always be stored in wellventilated spaces Oxygen Deficiency: A Big Risk Liquid nitrogen, when returned to the gaseous state, can displace oxygen from the air and can create an oxygen-deficient atmosphere under the right conditions. It may be prudent to install oxygen monitors in areas where liquid nitrogen is stored and ventilation is minimal. Oxygen Deficiency Precautions All cryogenic liquids should be used and stored in wellventilated areas. High concentrations of nitrogen reduce the breathable oxygen in the air. Filling between containers, leaking valves, and liquid tank venting are some examples that could lead to an oxygen deficient atmosphere. Handling Liquid Nitrogen Precautions: Always wear safety equipment, including heavy loose fitting leather or cryogenic gloves, and eye and face protection. High concentrations of escaping gas should not be allowed to collect in an enclosed area. Avoid prolonged breathing of cryogenic liquid vapors. Avoid rough handling of liquid containers A cold outside jacket indicates a loss of vacuum-contact supervisor or vendor Liquid cylinders should only be moved with proper handling equipment. Handling Liquid Nitrogen Prior to use, ensure the fittings on the regulator match the fittings on the liquid container Never use adaptors Never attempt to change or remove any fittings
Different Types of Dewars Liquid to Gas Conversion in Dewars The liquid-to-gas conversion rate is about 2.3% per day under perfect conditions, so the actual vaporization rate experienced can vary. If gas product is not used, pressure will build until it is released by a control valve. Note that this is a high pressure container, with the gauge marked for 350 psig. Liquid to Gas Conversion Since liquid is converted to gas at about 2.3% per day even under ideal container conditions, if the liquid is not used regularly, the vessel will be empty in a certain amount of time. It is important to estimate your use so the liquid will not be wasted. Storage in Cold Rooms Contrary to popular belief, storage of liquid containers in cold rooms will not slow down the liquid to gas conversion. Storage in cold rooms can actually create an oxygen deficient atmosphere if the room does not have adequate ventilation to remove the nitrogen gas generated. If there is a concern regarding oxygen deficiency in these areas, oxygen deficiency alarms should be installed in these areas. Warning Never plug, restrict, or remove any relief device. Never attempt to cap or seal a venting relief device in any way. Ice or frost buildup on a pressure relief valve can be removed with a damp cloth. (Wear proper Personal Protective Equipment (PPE) when removing the frost.) Be aware that frost buildup can freeze open a pressure relief valve, which can then lead to the complete venting of the entire contents of the dewar Elevator Transport Use freight elevator if possible If a passenger elevator is used, it should be locked out to all other users Do not transport a liquid container at any time in an elevator with any other personnel in the car unless they have a supplied air respirator
Liquid Withdrawl Caution!! Always wear a full face shield, goggles, leather or cryogenic gloves, safety shoes, and aprons when transferring liquid. Ensure that the liquid cannot collect in pants cuffs or travel down into shoes. Do not tuck cuffs into pants! Cuff gloves over sleeves. Transfer of liquids at pressures higher than 22 psig into open vessels such as small dewars can lead to excessive splashing. This could result in injury from freezing of the body part Liquid Withdrawl Ensure that withdrawal hose is equipped with a phase separator to prevent splashing. Check with supervisor or supplier. Never dispense liquid into an unapproved container, such as a Thermos bottle. It will shatter!