Welcome to this training session about arc flash. In this session, we ll talk about the hazards and risks of working around exposed, energized

Transcription

1 Welcome to this training session about arc flash. In this session, we ll talk about the hazards and risks of working around exposed, energized electrical equipment. We ll also discuss common arc flash hazards, general safe work practices for preventing an arc flash incident, and how to protect yourself from the hazards of an arc flash. This session provides information for unqualified workers, or those who lack the skills, knowledge, and training to work on or near exposed energized equipment. Qualified workers who work directly on or near such equipment can use this session to help them supervise the work of unqualified workers. 1

2 This presentation is designed for unqualified workers who work around, but not directly on, exposed, energized electrical equipment and parts. Only qualified persons are allowed to work on or test exposed, energized electrical equipment. Unqualified persons sometimes work around exposed, energized equipment but are not allowed to work directly on such equipment or within a certain restricted zone. A qualified person is someone who: Has demonstrated skills and knowledge in the construction and operation of electrical equipment and installations and the hazards involved and has training to identify the hazards and reduce the associated risk of injury or health effects of the energized equipment. This person also knows how to select and use the appropriate personal protective equipment, or PPE, for the task at hand. An unqualified person is: Not familiar with the construction and operation of the electrical equipment and hazards involved and has no formal training working with or on electrical equipment or the hazards involved. Basically, an unqualified person is anyone who is not designated as a qualified person. An unqualified person must never work directly on or too close to energized electrical equipment or parts. 2

3 By the end of the training session, you will be able to: Identify the causes and risks of arc flash; Follow safe work procedures to prevent arc flash; Identify and wear the proper PPE; and Respond appropriately to an arc flash incident. 3

4 An arc flash is a high-amperage short circuit that sends an electric current through the air. It occurs when an electric current flows between separate energized conducting surfaces or between an energized surface and ground for example, when circuit breakers and disconnects are opened and closed, when energized equipment is touched with a tool, or when equipment fails. Most electrical arc flash injuries do not occur in the presence of high-voltage (above 600 volts) electrical currents. Lowvoltage equipment sources (under 600 volts) account for most electrical arc flash occurrences. However, high-voltage incidents can be the most catastrophic. Electrical systems less than 50 volts are considered low risk for shock or arc flash. In an arc flash incident, an enormous amount of concentrated radiant energy emanates outward from the source of the arc, along with extremely hot gases, or arc plasma. A high-intensity flash is produced that can be bright enough to damage your eyesight. An instantaneous and powerful pressure wave that radiates from the source of the arc flash is also produced. The wave can cover several feet in half a second. The blast can send loose material like pieces of damaged equipment, tools, molten metal, and other objects flying through the air. The thermal blast generates a superheated ball of gas that can severely burn the human body and even melt metal. 4

5 Electrical burns, often severe, are a common injury from arc flash incidents. The flash itself can reach 35,000 degrees Fahrenheit, and the resultant fireball will severely burn skin and underlying tissue. The heat blast can cause severe burns several feet from the source. Severe burns can also occur from contacting surfaces, or from being hit by superheated projectiles, or when clothing or equipment catches fire from the thermal blast. The resulting pressure wave can damage your hearing. Equipment that is part of or exposed to the arc flash is often severely damaged. Also, flying debris can puncture or lacerate the skin. 5

6 You can be severely injured from an arc flash without touching the energized equipment! Workers have been injured while they were several feet away from the arc flash. The causes of an arc flash include: Tools dropped on conductors, circuit breakers, or other energized parts, which can cause a short circuit; Unintentional contact with electrical systems, such as a worker unintentionally touching an energized conductor thought to be de-energized; Improper work procedures, such as working on exposed, energized equipment when it should have been de-energized and locked out; Insulation failure where the fault current s magnetic effect causes conductors to separate, producing an arc; Testing electrical equipment with inappropriate instruments; and Distractions or inattentiveness to the risks posed by exposed, energized equipment. 6

7 Here are some additional causes of arc flash: Buildup of dust, impurities, and corrosion on insulating surfaces, which can provide a path for a current; Exposed to poorly maintained or defective equipment; Sparks produced during racking of breakers, replacement of fuses, and closing into faulted lines; and Birds or rodents that snap leads at connections. 7

8 The risk of an arc flash and your exposure to it depends on many factors. There is a higher risk of an arc flash incident when workers are: Exposed to energized parts repeatedly or for extended periods; Required to perform several tasks in the same work area during the same operation; Poorly trained in the specific tasks they must perform; or Diverted from paying attention to the task at hand. 8

9 The risk of an arc flash is lower when: Clear work practices are established and followed, such as written safety-related work practices and energized electrical work permits; Training is thorough and up to date; The right PPE rated for the job is worn at all times; Electrical equipment is routinely maintained and inspected; Workers are alert to the risks of their tasks; and Work is being done near electrical systems with less than 50 volts. 9

10 In this exercise, see if you can remember four arc flash effects. Four effects of arc flash are: Severe burns; Hearing loss; Excessive damage to equipment; and Puncture wounds and lacerations. 10

11 Now, see if you can remember at least three causes of arc flash. The causes of arc flash are: Dropped tools; Unintentional contact with electrical systems; Improper work procedures; Insulation failure; Voltage testing with inappropriate tool; Buildup of dust, impurities, and corrosion on insulating surfaces; Sparks produced during racking of breakers, replacement of fuses, and closing into faulted lines; Birds or rodents that break leads at connections; and finally Distracted workers. 11

12 Now it is time to ask yourself if you understand the information presented so far. Do you understand: What an arc flash is? Effects of a flash? What can cause a flash? And, your exposure risk? It is important for your safety that you understand this information. 12

13 Effective ways to prevent arc flash incidents from occurring are to: Leave all work on exposed, live electrical equipment to qualified persons only. A qualified person is one who has received documented training in the hazards of working on energized equipment in general and has been trained in the hazards of the particular equipment to be serviced and in the use and proper application of PPE. Only a qualified person is permitted to work on exposed, live electrical equipment. Create an electrically safe work condition by de-energizing all equipment, if possible, before beginning work. Follow safety-related work practices that we ll discuss later and that are described to you during the job briefing before you begin work. Use only the tools that have been designed and certified for the specific task at hand. Obey all warning signs and labels on or near electrical equipment. Report all unsafe conditions or defective equipment you see on or around electrical equipment. 13

14 In many cases, energized equipment will be de-energized and locked out by an authorized person before starting any work on it. You should be aware of these basic steps performed by the authorized person in the order shown and any other specific procedures for the particular equipment: 1. Determine all the possible sources of energy supply to the equipment. 2. After interrupting the load current, open disconnecting device(s) for each energy source. 3. Verify all elements of the disconnecting device are open or that circuit breakers are in the fully disconnected position, if possible. 4. Release any stored electrical energy in cables, batteries, and other electrical components. 5. Release any mechanical energy that is, kinetic or stored in springs, spinning blades, flywheels, or other energy stored in objects by the application of a force. 6. Apply lockout/tagout devices according to established procedures. 14

15 7. Test the voltage using only testing equipment that is in perfect working condition, has been verified to operate properly on a known voltage source, and that is rated for the equipment being tested. 8. Apply appropriate grounding devices as necessary with the possibility that stored electrical energy exists. 15

16 Never work around exposed, energized equipment at 50 volts or greater, except when: De-energizing or shutdown introduces additional or increased hazards, such as cutting power for ventilation to a workplace with a hazardous atmosphere; or It is not feasible to de-energize because of equipment design or operational limitations, such as when voltage testing is required for diagnostic purposes. Under most normal conditions, live parts that operate at less than 50 volts to ground need not be de-energized if there will be no increased exposure to electrical burns or to explosion due to electric arcs. There are instances where such voltage will require de-energizing, such as damp environments. 16

17 There are basic safe work practices and procedures you need to understand and follow before starting work in a work area with exposed, live or energized equipment. Each of these practices will be discussed in the next few minutes: Before you begin work, identify potential shock and arc flash hazards and observe workplace conditions that were described to you in the job briefing; Obey protection and approach boundaries; Wear appropriate PPE; Read the warning labels on equipment and make sure they are clear to you before continuing work, and get answers from the qualified worker to any questions you have; Observe signs and stay behind barriers and barricades; Use proper tools and portable equipment; Follow good housekeeping practices; and Keep clear of overhead lines. 17

18 When you enter a work space around exposed, energized equipment, look for potential shock, arc flash, and other hazards, and observe all site conditions that were described to you during the job briefing. Some things to watch for are: Voltage levels, which are displayed on warning labels or signs; Secondary voltage sources; Unusual conditions, such as damp or wet environments, hot enclosures, excessive noise, or unusual odors; Other workers and what they are doing; Clearing distances between electrical equipment, walls, and other objects or equipment in the area; and The condition and status of conductors, electrical boxes, fittings, and cables. For example, do all boxes have covers? Are all cables fastened near boxes or raceways? 18

19 When you are around exposed, energized equipment, do not cross the flash or shock boundaries without approval from a qualified person, and follow all precautions and personal protective equipment requirements. According to the National Fire Protection Association, or NFPA 70E, there are three boundaries that establish the level of arc flash burn exposure, or incident energy, and risk of an electrical shock a certain distance from an energy source. The arc flash or flash protection boundary is usually, but not always, the outermost established boundary from an energy source. It is the distance from the arc source to a surface, such as skin, where the incident energy could cause a second-degree burn. Unqualified persons are permitted inside this boundary when all precautions, including PPE, are followed and when supervised by a qualified person. The incident energy is the amount of thermal or heat energy that reaches a surface, like skin, during an electrical arc event. It is commonly shown on warning labels as calories per square centimeter at a certain distance. We ll cover this when we discuss warning labels. The limited approach boundary defines a distance from exposed live parts that could produce a shock. It may not be crossed by an unqualified person unless accompanied by a qualified person. The restricted approach boundary is usually but not always the closest of the three boundaries to energized equipment. It is the distance from exposed energized parts that may be crossed only by qualified persons using appropriate shock prevention techniques and equipment. 19

20 Wear PPE that is rated or otherwise appropriate for the electrical protection level and/or category required for the particular operation before entering the arc flash protection boundary or limited approach boundary, if permitted, such as: Head-area protection made of nonconductive material even hard hat liners must be arc-rated; Face shield that is arc-rated for the type of operation; Safety glasses; Voltage-rated gloves, with a heavy-duty leather glove over-glove for protection from burns over a rubber glove for shock protection; Leather footwear; and Arc-rated flame-resistant outer clothing don t wear any synthetic materials, such as nylon, acetate, or rayon, because it can burn or melt onto the skin. Use only pure cotton for undergarments that are covered by arc-rated clothing. Remember, do not wear metal buttons, clasps, or zippers they conduct electricity and can create additional electrical risks. 20

21 NFPA 70E establishes four categories of protective clothing and equipment rated to withstand specific levels of incident energy inside the arc flash boundary. PPE is rated for arc flash it does not have a rating for the explosive effects of an arc blast. 21

22 Category 1 clothing and equipment are rated to withstand at least 4 calories per square centimeter incident energy, and it requires a combination of eight items: 1. Arc-rated shirt; 2. Arc-rated pants or coveralls; 3. Arc-rated face shield or arc flash suit hood; 4. Arc-rated outer clothing such as jacket, parka, rain gear, or hard hat liner; 5. Arc-rated hard hat; 6. Insert-type hearing protection; 7. Rubber-insulating gloves with leather outer gloves and leather footwear; and 8. Safety glasses or goggles. 22

23 Category 2 PPE is rated to withstand at least 8 calories per square centimeter and requires everything in Category 1, plus: Arc-rated balaclava with the face shield if a suit hood is not worn; and Arc-rated hood at 12 cal/cm 2. 23

24 Category 3 PPE can withstand at least 25 calories per square centimeter and includes everything from Category 2, plus: Arc-rated pants and coverall; Flash suit jacket and pants; Suit hood (no shield); and Rubber-insulating gloves with outer leather protectors, or gloves. 24

25 Category 4 PPE can withstand at least 40 calories per square centimeter and includes everything from Category 3, but with a higher rating, to withstand at least 40 calories per square centimeter. 25

26 PPE will provide the protection it is designed for only when it is used as directed and maintained in good condition, such as: It must fit properly to allow unrestricted body movement; It must cover all potentially exposed areas; Inspect it before each use; Follow PPE manufacturer s care, cleaning, and maintenance instructions; and Store it in a way that prevents physical damage or damage from deteriorating agents or flammable materials. 26

27 Warning labels are placed on all electrical equipment that poses a potential shock and arc flash hazard. NFPA 70E states that labels should include at least: The nominal system voltage, such as 480 volts of alternating current, as shown on the example label. Arc flash (or flash protection) boundary. The example label shows 24 inches as the flash hazard (or protection) boundary. It means 24 inches from the source of an arc flash, a person would receive incident energy of 1.2 calories per square centimeter. Either the available incident energy and minimum arc rating of clothing or the required category of PPE. Labels created since 2011 will include either the incident energy and corresponding working distance, or the arc flash PPE category for the equipment, but not both. The label in this example shows the incident energy at a working distance of 18 inches. Also shown in this illustration are specific recommendations for the type and weight of protective clothing and equipment for the voltage and other conditions. It does not show the category of PPE. Other information may include specific PPE required within the limitedor restricted-approach shock boundaries, the minimum arc rating of clothing, and site-specific level of PPE. 27

28 Even when you are not involved with work on or around exposed, energized electrical equipment, you may be exposed to electrical hazards if you pass through an area where such work is being done. You should be aware of the following techniques to warn you of the hazards, even when you are outside of a flash protection or limited-approach boundary. In addition to the warning or danger labels on energized equipment, look around the work area for accident prevention tags, safety signs, and symbols that will warn about electrical hazards. For example, look for signs that say, DANGER HIGH VOLTAGE and/or the lightning bolt symbol that represents an electrical hazard is near. Examples of tags include DANGER LIVE WIRE written on a tag tied to a live wire. Barricades are used to physically mark out the area where a hazard exists, such as cones connected by warning tape. They are not barriers capable of stopping a person from passing through but establish a visibly marked line not to cross. In situations where signs and barricades can t provide adequate warning, an attendant will be stationed to signal or alert others to stay out of the work area. The attendant should not have any other job while on duty. Sometimes equipment that is safely de-energized and locked out looks similar to other equipment that is energized in the same work area. In these cases, the entire work area may have warning signs or attendants to make sure no one mistakenly gets near the look-alike equipment. 28

29 Follow these procedures when performing housekeeping duties near exposed, energized electrical equipment: Unless you are the qualified person, never conduct housekeeping operations within the limited-approach boundary; only qualified persons may do so. Use nonconductive cleaning materials whenever possible. For example, use an alternative to steel wool to avoid the chance of metal contact with an energized part. Also, remember that water is a conductive liquid and may pose a hazard. Avoid using any flammable materials in the work area. Make sure doors to electrical equipment are closed. Replace damaged electrical tools or devices, cords, plugs, receptacles, or connectors before using them. Identify and remove all environmental hazards, such as water on the floor, or oil on the floor, which can ignite or indicate a leak in an oilfilled breaker or transformer. 29

30 There are instances where unqualified workers might be working near energized overhead power lines. When an unqualified person is working close to energized power lines, either standing on the ground or elevated, the person and any conductive object he or she may carry or contact must not come closer to the line than: 10 feet for up to a 50-kilovolt line; or Greater distances away for lines rated higher than 50 kilovolts consult with a qualified person to determine your safe distance for any situation with overhead power lines. 30

31 Ask yourself if you understand the information presented so far. Do you understand about: Effects, causes, and risks of arc flash? Electrically safe work conditions? Safety-related work practices? PPE? 31

32 Follow these precautions in addition to the safety-related work practices already discussed for working around exposed, energized electrical equipment: Use only nonconductive tools when working near or in the flash protection or shock approach boundaries. As discussed earlier but worth repeating only wear clothes that do not conduct electricity for example, no metal zippers on any clothing. The work area should be well-lit so you can clearly recognize and stay clear of electrical hazards. Do not defeat or try to circumvent electrical interlock devices. Never reach with hands or tools into or behind areas where you cannot see exposed energized parts. 32

33 If there is an arc flash incident and you are uninjured and able to respond, take the following measures to minimize further damage or injury: Call for help sound the alarm. Turn off the power supply if you are trained and able to do so. Extinguish flames on a person first, then on equipment if the fire is incipient (early stages and small). Make sure anyone injured is not connected in any way to energized equipment or parts before you touch the person. Implement the contact release procedure if you are trained to do so, and have the right equipment otherwise, wait for emergency responders. If an injured person is not breathing, begin cardiopulmonary resuscitation, or CPR, but make sure there are no serious burn injuries to the chest region. Administer other first aid, including the use of an automated external defibrillator if you are trained to do so. 33

34 Damaged equipment can result in serious electrical hazards. Stop using, and report to your supervisor: Any damaged electrical covers on electrical panels, junction boxes, and other equipment where live electrical parts and wiring may be exposed; Damaged tools that may expose live electrical parts and wiring to a person; Damaged equipment, such as circuit breakers, connectors, switches; or Improper equipment placement, such as an extension cord over energized equipment. 34

35 In this exercise, describe at least three safe work practices. Some practices are: Don t enter the flash or shock approach boundaries unless authorized to do so by a qualified person and you are wearing all appropriate PPE. Wear the appropriate PPE for protection against arc flash and other known hazards. No housekeeping activities are allowed within the limited-approach shock boundary unless you are qualified and properly protected. Observe the workplace for any unusual conditions, such as excessive noise, hot enclosures, or unusual odors. Use only nonconductive cleaning materials around energized equipment or parts. Obey all warning labels, signs, barricades, or attendants. 35

36 Never underestimate the risks and hazards of an arc flash associated with working on exposed, energized equipment. The long-term physical and emotional costs of ignoring the hazards and not following safe work practices are high and often permanent. Here are a few key points to remember when working around exposed, energized electrical equipment. Always inspect equipment and work areas for arc flash hazards and risks each time you enter an area with live electrical equipment. Keep an eye out for arc flash warning labels. Human error is a major cause of arc flash incidents, such as: Dropped tools, contact with an electrical part, wrong test equipment, and improper work practices. An effective way to prevent arc flash incidents is to create an electrically safe work condition by de-energizing exposed, energized equipment. Follow safe work practices without fail, and do not deviate from them at all. They could save your life and years of pain and suffering. Wear all required PPE make sure it is in excellent working condition and rated for the specific use that your work calls for. And finally, always report and don t use damaged electrical equipment, testing equipment, and other tools. 36