Transcript Electrical Hazards - Bowling Green State University

General Electrical Safety
BGSU
Environmental
Health and Safety
Agenda
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Electrical Injuries
Classification of Exposure
Electrical Hazards
Electrical Hazard Control
Electrical Injuries
Electrocutions:
 1970s: 600-700 per year
 1990s: 300-400 per year (NIOSH, 1998)
5th leading cause of occupational fatalities.
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7% of total deaths, ranked after motor vehicle
crashes, homicide, falls, and mechanical trauma.
Each year, electrical accidents cause as many as
165,380 electrical fires and 7,000 injuries.
Classification of Exposure
High Voltage
 >600 volts: typically associated with “outdoor”
electrical transmission.
Accounts for 60% of electrocutions (OSHA).
Note: some people classify >480 volts as high voltage.
Low Voltage:
 <600 volts: typically associated with “indoor”
electrical service.
Accounts for 32% of electrocutions (OSHA).
Low voltage does not imply safe voltage.
Electrical Hazards
• Shock
:Conductors vs.
Resistors
:Grounding
:The Ground Fault
Accident
:GFCIs
• Burns
• Falls
• Fire
Electrical Hazards
Electrical Shock
• Shock occurs when current passes through
the body.
• Severity of the shock depends on:
– Path of current
– Amount and type of current
– Duration of exposure
• Electrocution is a fatal electrical injury.
Electrical Hazards
Conductors vs. Resistors
• All materials exhibit some resistance to
electrical current.
• Materials with low resistance are called
conductors (ex. copper, aluminum, gold,
water).
• Materials with high resistance are called
resistors (ex. rubber, glass, air, most plastics).
Electrical Hazards
Conductors vs. Resistors continued…
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Electricity wants to find the path of least
resistance to the ground.
Human tissues and body fluids are relatively
good conductors because of high water
content.
So if a person touches an energized bare
wire or faulty equipment while grounded,
electricity will instantly pass through the body
to the ground, causing a harmful, potentially
fatal, shock.
Electrical Hazards
Grounding
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Grounding is a method of protecting
employees from electric shock.
By grounding an electrical system, a lowresistance path to earth through a ground
connection is intentionally created.
This path offers low resistance and has
sufficient current-carrying capacity to prevent
the build-up of hazardous voltages.
A three pronged cord offers a grounding
connection.
Electrical Hazards
Grounding continued…
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White wire (neutral or common
wire), returns the power.
Black wire (hot wire), is
connected to the switch and
fuse and carries the power.
Green (or ground wire).
Three wires for each cord and
terminal.
A two prong plug has a hot
prong and a return prong, no
ground prong.
In any case, never remove the
third (grounding) prong from
any three-prong piece of
equipment.
Electrical Hazards
The “Ground Fault” Accident
• A ground fault accident occurs when a
person touches or grasps an electrically
energized object while the feet or other body
parts are in contact with the ground or a
grounded surface.
• In some cases a ground fault accident
occurs when the opposite hand touches
the ground or a grounded object.
Electrical Hazards
Ground Fault Accident Example
A woman was putting up her Christmas tree.
When she went to plug in the strands of
lights, her finger was touching the metal
prong on the plug. Her other hand was
touching a metal coffee table leg for support.
The current went through her body as a
result, causing cardiac arrest and death.
Electrical Hazards
Electrical Shock Example
A worker came out of the bathroom with her
hands dripping wet, and reached down to
plug in a lamp. She got a shock but survived.
The same worker was cleaning walls with a
sponge and a bucket of soapy water. Not
paying attention she washed over an outlet,
which also gave her a shock. The shock was
intensive enough to stop her breathing. She
survived this time as well.
Electrical Hazards
Ground-Fault Circuit-Interrupters (GFCI’s)
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GFCI’s are to be used when using
electrical equipment in a wet environment.
GFCI’s are designed to detect any
leakage of current in an electrical circuit.
GFCI’s turn off or “trip” the circuit
whenever the leakage is greater than
5/1000 of an ampere.
For comparison two 60 Watt light bulbs
draw a total of 1 ampere of current.
Electrical Hazards
Ground-Fault Circuit-Interrupters (GFCI’s)
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Three types of GFCI’s
A GFCI receptacle used in place of standard
receptacle.
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A portable GFCI plugs into a standard
receptacle.
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A GFCI circuit breaker combines leakage
current detection with the function of a
circuit breaker.
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Whenever working in a wet area, or
outdoors, employees should use one of
these types of GFCI’s.
Electrical Hazards
Electrical Burns
• Most common nonfatal electrical injury.
• Types:
– Internal: “deep tissue”.
– Skin: “entry” and “exit” points.
– Arc: “flash” burns from heat and radiant energy.
• Common sites of visible skin burns are the hands and
feet.
Electrical Hazards
Electrical Burns continued…
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Circuits may produce electrical burns with
relatively massive amounts of tissue
destruction by heating the tissues.
This is due to the physical property of friction
from the passage of electrons and by
destruction of cell membranes by producing
holes in the membranes.
Electrical Hazards
Electrical Burns Example
A worker was mounting a large mirror onto
the wall of an office. He was using a metal
power tool which accidentally severed a wire
causing a shock and massive burns. The
victim exhibited deep tissue destruction
along the entire current path, along with
surface tissue damage at the point of entry
and exit.
Electrical Hazards
Falls
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Involuntary muscle
contractions can
“throw” workers and
cause falls.
If working at elevation,
the fall may cause
serious injury or
death.
Electrical Hazards
Example of a Fall Due to Electricity
A worker fell from the top of a 12-story building and
landed on the concrete below. A short-circuited
electric drill was found dangling from the building's
top floor. Detectives discovered that the grounding
prong was missing from the drill's plug. A nail was
lodged in the rubber tread of the work boot, allowing
electricity to flow through the victim's body to the
ground. The electrical current caused muscle
contractions strong enough to throw the man from
the building, resulting in death.
Electrical Hazards
Fire
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In the United States 25% of fires are
caused by electricity.
A build-up of dust, trash and spider webs
increases the potential for fire to start in
the electrical system.
Unprotected light bulbs in work areas are
another potential hazard. They can be hit,
broken and cause a fire.
Electrical wiring can be hit when drilling
holes or driving nails in walls causing a
fire.
Electrical Hazards
Fires continued…
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Many fires result from defects in, or misuse
of the power delivery system.
Wiring often fails due to faulty installation,
overloading, physical damage, aging and
deterioration by chemical action, heat,
moisture and weather.
Such wiring should be replaced and new
circuits installed.
Electrical Hazards
Fires continued…
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Typical home and office electrical systems
run like this:
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The electrical service enters the house and
connects to a main electrical panel.
From the main electrical panel, wires run in
different directions throughout the house/building
to power lights, outlets, ceiling fans, air
conditioners, and various other direct-wired
electrical appliances.
Electrical Hazards
Fires continued…
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When electricity flows through a wire, the wire
heats up because of its resistance to the flow of
electrical current.
Both the size of the wire and how many electrical
devices on the circuit are drawing electricity affect
the amount of heat generated in the wire.
This is why electrical fuses or circuit breakers are
used in the main electrical panel. Their function is
to sense the overloading of circuits (and short
circuits) and shut off power to that branch circuit
before the wires get too hot and start a fire.
Electrical Hazards
Fires continued…
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To keep the wire from getting too hot and starting a
fire, circuit wiring attempts to contain the amount of
electrical load on the branch circuit by limiting the
number of potential electrical appliances that can be
running at the same time on that circuit.
For example, only so many outlets are put on one
branch circuit or larger pieces of electrical
equipment are put on circuits dedicated to that
equipment only.
The homeowner or worker can plug in and run too
many appliances on the same circuit at one time
and overload the circuit.
Electrical Hazards
Fires continued…
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Each circuit must be protected by a fuse or
circuit breaker that will blow or “trip” when
its safe carrying capacity is surpassed.
If a fuse blows or circuit breaker trips
repeatedly while in normal use (not
overloaded), check for shorts and other
faults in the line or devices.
Do not resume use until the trouble is
fixed.
Electrical Hazards
Fires continued…
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It is hazardous to overload
electrical circuits by using
extension cords and multiplug outlets.
Use extension cords only
when necessary and make
sure they are heavy enough
for the job.
Avoid creating an “octopus”
by inserting several plugs into
a multi-plug outlet connected
to a single wall outlet. (CDC)
Electrical Hazards
Fires continued…
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Dimmed lights, reduced output from heaters
and poor television pictures are all symptoms
of an overloaded circuit.
Keep the total load at any one time safely
below maximum capacity.
When using a high wattage device such as a
heater, iron or power tool, turn off all
unnecessary lights and devices.
Try to connect into a circuit with little
electrical power demand.
Electrical Hazards
Fire continued…
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Property damage is a
primary event resulting
from fire.
Injuries and fatalities
may result from fire
(secondary events).
Electrical Hazards
Electrical Fire Example at B.G.S.U.
In McDonald North, a fire broke out in a
student dorm room. A drop cord was found
to be the cause. The cord had been
damaged by the bed post, leaving frayed
wires. The power ran through a spare
breaker because the circuit was very hot.
The fire was detected by the smoke and heat
detectors and help arrived in time for the fire
to be extinguished. No injuries, but damage
to the wall and carpet.
Electrical Hazard Control
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Extension cords should only be
used on a temporary basis in
situations where fixed wiring is
not feasible.
DO NOT use extension cords as
permanent wiring. They may not
be able to carry the load.
However, if it is necessary to use
an extension cord, never run it
across walkways or aisles.
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It causes a potential tripping
hazard.
It wears down the insulation.
Electrical Hazard Control continued…
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Wall receptacles should be
designed and installed so that
no current-carrying parts will
be exposed, and outlet plates
should be kept tight to
eliminate the possibility of
shock.
Replace or repair electrical
appliances that over heated,
sparked, shorted out, smoked
or have damaged cords or
cracked equipment.
Electrical Hazard Control continued…
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If wires are exposed, they may cause a
shock to a worker comes into contact
with them.
Cords should not be hung on nails, run
over or wrapped around objects,
knotted or twisted. This may break the
wire or insulation.
Short circuits are usually caused by
bare wires touching due to breakdown
of insulation.
Electrical tape or any other kind of tape
is not adequate!
Cords in areas of water or other
conductive liquid must be approved for
those locations.
Electrical Hazard Control continued…
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When the outer jacket of a cord is damaged,
the cord may no longer be water-resistant.
The insulation can absorb moisture, which
may then result in a short circuit or excessive
current leakage to the ground.
These cords should be replaced
immediately.
Electric cords should be examined on a
routine basis for fraying and exposed wiring.
Electrical Hazard Control continued…
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Electrical cords should be examined visually before
use on any shift for external defects such as:
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fraying and exposed wiring
loose parts
deformed or missing parts
damage to outer jacket or insulation
evidence of internal damage such as pinched or
crushed outer jacket
If any defects are found the electric cords should be
removed from service immediately.
Electrical Hazard Control continued…
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Pull the plug not the cord. Pulling the cord
could break a wire, causing a short circuit.
Electrical Hazard Control continued…
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Plug your microwave or any other
large appliances into an outlet that is
not shared with other appliances.
Do not tamper with fuses as this is a
potential fire hazard.
Do not overload circuits as this may
cause the wires to heat and ignite
insulation or other combustibles.
Electrical Hazard Control continued…
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Keep office equipment properly cleaned and
maintained.
Ensure lamps are free from contact with
flammable material.
Always use lights bulbs with the
recommended wattage for your lamp and
ceiling fixtures.
Be aware of the odor of burning plastic or
wire.
Electrical Hazard Control continued…
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ALWAYS follow the manufacturer
recommendations when using or installing
new office equipment.
Wiring installations should always be made
by a licensed electrician or other qualified
person.
All electrical appliances should have the
label of a testing laboratory.
Water is VERY conductive!
Reference: http://www.safteng.net
Overloading!
Reference: http://www.safteng.net
Missing grounding prong!
Reference: http://www.safteng.net
Missing outlet cover!
Reference: http://www.safteng.net
Electrical tape is not a fix!
Reference: http://www.safteng.net
Pinched cord!
Damaged casing!
Reference: http://www.safteng.net
Any Questions?
Where to Get More Information
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http://www.osha.gov. Occupational Safety
and Health Administration.
http://www.bgsu.edu/offices/envhs.
Bowling Green State University
372-2171