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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

Electrical Safety

Çağlar Girit

Zettl Group Safety Talk

1/18/07

understanding the risks
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

physiological effects
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: ???
physiological effects cont d
Physiological Effects (cont’d)

BODILY EFFECT DIRECT CURRENT (DC) 60 Hz AC 10 kHz AC

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Slight sensation Men = 1.0 mA 0.4 mA 7 mA

felt at hand(s) Women = 0.6 mA 0.3 mA 5 mA

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Threshold of Men = 5.2 mA 1.1 mA 12 mA

perception Women = 3.5 mA 0.7 mA 8 mA

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Painful, but Men = 62 mA 9 mA 55 mA

voluntary muscle Women = 41 mA 6 mA 37 mA

control maintained

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Painful, unable Men = 76 mA 16 mA 75 mA

to let go of wires Women = 51 mA 10.5 mA 50 mA

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Severe pain, Men = 90 mA 23 mA 94 mA

difficulty Women = 60 mA 15 mA 63 mA

breathing

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Possible heart Men = 500 mA 100 mA

fibrillation Women = 500 mA 100 mA

after 3 seconds

---------------------------------------------------------------

DC vs AC?

physiological effects cont d6
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
protection procedures and equipment
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
shock rescue procedures
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.
electrical safety reminders
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.
resources
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