Transcript Electrical Safety - University of California, Berkeley

Electrical Safety
Çağlar Girit
Zettl Group Safety Talk
1/18/07
Understanding the Risks
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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
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)
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
DC vs AC?
after 3 seconds
---------------------------------------------------------------
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
• 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
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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
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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
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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