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Electrical Safety

Electrical Safety. Çağlar Girit Zettl Group Safety Talk 1/18/07. Understanding the Risks. Electrical hazards, while a fraction of total workplace injuries, are more likely to result in death than injuries from other causes.

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Electrical Safety

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  1. Electrical Safety Çağlar Girit Zettl Group Safety Talk 1/18/07

  2. Understanding the Risks • Electrical hazards, while a fraction of total workplace injuries, are more likely to result in death than injuries from other causes. • Electrical accidents on the job cause an average of 13 days away from work and nearly one fatality every day. • Approximately 62 percent of an estimated 32,807 nonfatal electrical injuries occurring between 1992 and 1998 were classified as electric shock and 38 percent as electric burns. • The nonfatal workplace incidents that cause the highest number of days away from work include contact with an electrical current or a machine, tool, appliance or light fixture (38 percent), and contact with wiring, transformers or other electrical components (33 percent). • Nonfatal electrical injury occurs most often to those who work with machines or tools and around electrical wiring other than power lines. Source: “Occupational Electrical Injuries in the US, 1992–1998” published in the Journal of Safety Research

  3. Physiological Effects Burns • Internal burning of organs (body is a resistor dissipating heat) • External arcs • Shock • Muscle contraction and tetanus (“froze on the circuit”) • Heart: ventricular fibrillation • Lung: respiratory failure • Brain: ???

  4. Physiological Effects (cont’d) BODILY EFFECT DIRECT CURRENT (DC) 60 Hz AC 10 kHz AC --------------------------------------------------------------- Slight sensation Men = 1.0 mA 0.4 mA 7 mA felt at hand(s) Women = 0.6 mA 0.3 mA 5 mA --------------------------------------------------------------- Threshold of Men = 5.2 mA 1.1 mA 12 mA perception Women = 3.5 mA 0.7 mA 8 mA --------------------------------------------------------------- Painful, but Men = 62 mA 9 mA 55 mA voluntary muscle Women = 41 mA 6 mA 37 mA control maintained --------------------------------------------------------------- Painful, unable Men = 76 mA 16 mA 75 mA to let go of wires Women = 51 mA 10.5 mA 50 mA --------------------------------------------------------------- Severe pain, Men = 90 mA 23 mA 94 mA difficulty Women = 60 mA 15 mA 63 mA breathing --------------------------------------------------------------- Possible heart Men = 500 mA 100 mA fibrillation Women = 500 mA 100 mA after 3 seconds --------------------------------------------------------------- DC vs AC?

  5. Physiological Effects (cont’d) Body contact resistances • Wire touched by finger: 40,000 Ω to 1,000,000 Ω dry, 4,000 Ω to 15,000 Ω wet. • Wire held by hand: 15,000 Ω to 50,000 Ω dry, 3,000 Ω to 5,000 Ω wet. • Metal pliers held by hand: 5,000 Ω to 10,000 Ω dry, 1,000 Ω to 3,000 Ω wet. • Contact with palm of hand: 3,000 Ω to 8,000 Ω dry, 1,000 Ω to 2,000 Ω wet. • 1.5 inch metal pipe grasped by one hand: 1,000 Ω to 3,000 Ω dry, 500 Ω to 1,500 Ω wet. • 1.5 inch metal pipe grasped by two hands: 500 Ω to 1,500 kΩ dry, 250 Ω to 750 Ω wet. • Hand immersed in conductive liquid: 200 Ω to 500 Ω. • Foot immersed in conductive liquid: 100 Ω to 300 Ω. • Hand or foot contact, insulated with rubber: 20 MΩ typical. • Foot contact through leather shoe sole (dry): 100 kΩ to 500 kΩ • Foot contact through leather shoe sole (wet): 5 kΩ to 20 kΩ

  6. Protection Procedures and Equipment • Remove jewelry or any items that could improve electrical contact • Use rubber gloves and boots • De-energize circuit and ensure that it stays that way until all work is complete • Check to make sure circuit is not live • Use only one hand to avoid current path across body • Household safety items: GFCI (ground-fault circuit interrupter) and ground prong

  7. Shock Rescue Procedures • DO NOT TOUCH FROZEN PERSON or you can become frozen. • Deenergize the circuit (flip the circuit breaker) if possible. • Call for help and get first-aid supplies • Separate the person from the energy source. • Make sure you and the victim are in a safe zone - not in contact with any electrical source, away from downed or broken wires. • Never grab the person or pull the person off the current with your hands; you might become part of the circuit and become injured as well. • Use a dry wood broom, leather belt, plastic rope or something similar that is non-conductive such as wood or plastic cane with hook on the end to free the person from the energy source • Administer first aid: apply mouth-to-mouth resuscitation and/or CPR • Keep the victim lying down, warm and comfortable to maintain body heat until help arrives. Do not move the person in case of injury to neck or back. • If the victim is unconscious, put him/her on side to let fluids drain. • Make sure the victim receives professional medical attention (person shocked could have heart failure hours later) Apply burn victim first-aid.

  8. Electrical Safety Reminders • Re-route electrical cords or extension cords so they don't run across the aisle/corridor or over pipes or through doors. • Turn off and unplug equipment before removing the protective cover to clear a jam, replace a part, etc. • Don't use an electrical outlet or switch if the protective cover is ajar, cracked, or missing. • Use dry hands and stand on a dry surface when using electrical equipment. • Remove any combustible materials, such as paper and wood from the area. Be sure flammable liquids and gases are secured away from the area when the appliance is in use. • Never put conductive metal objects into energized equipment. • Remove cord from the outlet by pulling the plug instead of pulling on the cord. • Don't carry equipment by the cord - only by the handle or base. • Be sure extension cords are properly rated for the job and used only temporarily. • Use extension cords with 3-prong plugs to ensure the equipment is grounded. Never remove the grounding post from a 3-prong plug so you can put it into a 2-prong. • Don't overload extension cords, multi-outlet strips or wall outlets (15 A/120 VAC) • Take seriously any warning signs, barricades or guards posted when electrical equipment is being repaired, installed, etc.

  9. Resources • LBL Health and Safety Manual • LLNL ESH Electrical Safety Manual • All About Circuits Electrical Safety • Electrical Safety Foundation Intl • MIT EHS electrical safety • Safe Electricity website

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