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You will receive an electrical shock if a part
of your body completes an electrical circuit by...
- Touching a live wire and an electrical ground, or
- Touching a live wire and another wire at a different
voltage.
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Consumer Education : Electricity can KILL .
Dangers of Electrical Shock |
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The severity of injury from electrical shock
depends on the amount of electrical current and the length of
time the current passes through the body. For example, 1/10 of
an ampere (amp) of electricity going through the body for just 2
seconds is enough to cause death. The amount of internal current
a person can withstand and still be able to control the muscles
of the arm and hand can be less than 10 milliamperes (milliamps
or mA). Currents above 10 mA can paralyze or "freeze" muscles.
When this "freezing" happens, a person is no longer able to
release a tool, wire, or other object. In fact, the electrified
object may be held even more tightly, resulting in longer
exposure to the shocking current. For this reason, hand-held
tools that give a shock can be very dangerous. If you can't let
go of the tool, current continues through your body for a longer
time, which can lead to respiratory paralysis (the muscles that
control breathing cannot move). You stop breathing for a period
of time. People have stopped breathing when shocked with
currents from voltages as low as 49 volts. Usually, it takes
about 30 mA of current to cause respiratory paralysis.
Currents greater than 75 mA may cause ventricular fibrillation
(very rapid, ineffective heartbeat). This condition will cause
death within a few minutes unless a special device called a
defibrillator is used to save the victim. Heart paralysis occurs
at 4 amps, which means the heart does not pump at all. Tissue is
burned with currents greater than 5 amps.
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The table shows what usually happens for a range
of currents (lasting one second) at typical household voltages.
Longer exposure times increase the danger to the shock victim.
For example, a current of 100 mA applied for 3 seconds is as
dangerous as a current of 900 mA applied for a fraction of a
second (0.03 seconds). The muscle structure of the person also
makes a difference. People with less muscle tissue are typically
affected at lower current levels. Even low voltages can be
extremely dangerous because the degree of injury depends not
only on the amount of current but also on the length of time the
body is in contact with the circuit.
LOW VOLTAGE DOES NOT MEAN LOW HAZARD!
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| Effects of Electrical
Current*
on the Body
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Sometimes high voltages lead to additional
injuries. High voltages can cause violent muscular contractions.
You may lose your balance and fall, which can cause injury or
even death if you fall into machinery that can crush you. High
voltages can also cause severe burns (as seen on pages 9 and
10).
At 600 volts, the current through the body may be as great as 4
amps, causing damage to internal organs such as the heart. High
voltages also produce burns. In addition, internal blood vessels
may clot. Nerves in the area of the contact point may be
damaged. Muscle contractions may cause bone fractures from
either the contractions themselves or from falls. |
A severe shock can cause much more damage to
the body than is visible. A person may suffer internal bleeding
and destruction of tissues, nerves, and muscles. Sometimes the
hidden injuries caused by electrical shock result in a delayed
death. Shock is often only the beginning of a chain of events.
Even if the electrical current is too small to cause injury,
your reaction to the shock may cause you to fall, resulting in
bruises, broken bones, or even death.
The length of time of the shock greatly affects
the amount of injury. If the shock is short in duration, it may
only be painful. A longer shock (lasting a few seconds) could be
fatal if the level of current is high enough to cause the heart
to go into ventricular fibrillation. This is not much current
when you realize that a small power drill uses 30 times as much
current as what will kill. At relatively high currents, death is
certain if the shock is long enough. However, if the shock is
short and the heart has not been damaged, a normal heartbeat may
resume if contact with the electrical current is eliminated.
(This type of recovery is rare.) |
The amount of current passing
through the body also affects the severity of an electrical
shock. Greater voltages produce greater currents. So, there is
greater danger from higher voltages. Resistance hinders current.
The lower the resistance (or impedance in AC circuits), the
greater the current will be. Dry skin may have a resistance of
100,000 ohms or more. Wet skin may have a resistance of only
1,000 ohms. Wet working conditions or broken skin will
drastically reduce resistance. The low resistance of wet skin
allows current to pass into the body more easily and give a
greater shock. When more force is applied to the contact point
or when the contact area is larger, the resistance is lower,
causing stronger shocks.
The path of the electrical current through the body affects the
severity of the shock. Currents through the heart or nervous
system are most dangerous. If you contact a live wire with your
head, your nervous system will be damaged. Contacting a live
electrical part with one hand-while you are grounded at the
other side of your body-will cause electrical current to pass
across your chest, possibly injuring your heart and lungs.
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There have been cases where an arm or leg is
severely burned by high-voltage electrical current to the point
of coming off, and the victim is not electrocuted. In these
cases, the current passes through only a part of the limb before
it goes out of the body and into another conductor. Therefore,
the current does not go through the chest area and may not cause
death, even though the victim is severely disfigured. If the
current does go through the chest, the person will almost surely
be electrocuted. A large number of serious electrical injuries
involve current passing from the hands to the feet. Such a path
involves both the heart and lungs. This type of shock is often
fatal. |
Summary of Section 2
The danger from electrical shock depends on...
- the amount of the shocking
current through the body,
- the duration of the shocking
current through the body, and
- the path of the shocking
current through the body.
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Section 3
Burns Caused by Electricity |
The most common
shock-related, nonfatal injury is a burn. Burns caused by
electricity may be of three types: electrical burns, arc
burns, and thermal contact burns. Electrical burns can
result when a person touches electrical wiring or equipment that
is used or maintained improperly. Typically, such burns occur on
the hands. Electrical burns are one of the most serious injuries
you can receive. They need to be given immediate attention.
Additionally, clothing may catch fire and a thermal burn may
result from the heat of the fire.
Arc-blasts occur when powerful, high-amperage currents arc
through the air. Arcing is the luminous electrical discharge
that occurs when high voltages exist across a gap between
conductors and current travels through the air. This situation
is often caused by equipment failure due to abuse or fatigue.
Temperatures as high as 35,000°F have been reached in
arc-blasts.
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are three primary hazards associated with an arc-blast.
(1) Arcing gives off thermal radiation (heat) and intense light, which
can cause burns. Several factors affect the degree of injury, including
skin color, area of skin exposed, and type of clothing worn. Proper
clothing, work distances, and overcurrent protection can reduce the risk
of such a burn.
(2) A high-voltage arc can produce a considerable pressure wave blast. A
person 2 feet away from a 25,000-amp arc feels a force of about 480
pounds on the front of the body. In addition, such an explosion can
cause serious ear damage and memory loss due to concussion. Sometimes
the pressure wave throws the victim away from the arc-blast. While this
may reduce further exposure to the thermal energy, serious physical
injury may result. The pressure wave can propel large objects over great
distances. In some cases, the pressure wave has enough force to snap off
the heads of steel bolts and knock over walls.
(3) A high-voltage arc can also cause many of the copper and aluminum
components in electrical equipment to melt. These droplets of molten
metal can be blasted great distances by the pressure wave. Although
these droplets harden rapidly, they can still be hot enough to cause
serious burns or cause ordinary clothing to catch fire, even if you are
10 feet or more away.
Electrical Fires
Electricity is one of the most common causes of fires and
thermal burns in homes and workplaces.
Defective or misused electrical equipment is a major cause of
electrical fires. If there is a small electrical fire, be sure
to use only a Class C or multipurpose (ABC) fire extinguisher,
or you might make the problem worse. All fire extinguishers are
marked with letter(s) that tell you the kinds of fires they can
put out. Some extinguishers contain symbols, too.
The letters and symbols are explained below (including
suggestions on how to remember them)
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A (think: Ashes) = paper, wood, etc.
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B (think: Barrel) = flammable liquids |
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C (think: Circuits) = electrical fires |
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Here are a couple of fire extinguishers at a worksite. Can you
tell what types of fires they will put out?However, do not
try to put out fires unless you have received proper training.
If you are not trained, the best thing you can do is evacuate
the area and call for help.
Thermal burns may result if an explosion occurs when electricity
ignites an explosive mixture of material in the air. This
ignition can result from the buildup of combustible vapors,
gasses, or dusts. Occupational Safety and Health Administration
(OSHA) standards, the NEC, and other safety standards give
precise safety requirements for the operation of electrical
systems and equipment in such dangerous areas. Ignition can also
be caused by overheated conductors or equipment, or by normal
arcing at switch contacts or in circuit breakers.
Summary of Section 3
Burns are the most common injury caused by electricity. The
three types of burns are . . .
- electrical burns,
- arc burns, and
- thermal contact burns.
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First Aid
Fact Sheet |
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What Should I Do If a
Co-Worker Is Shocked or Burned by Electricity?
Shut off the electrical current if the victim is still in
contact with the energized circuit. While you do this, have
someone else call for help. If you cannot get to the switchgear
quickly, pry the victim from the circuit with something that
does not conduct electricity such as dry wood. Do not touch
the victim yourself if he or she is still in contact with an
electrical circuit! You do not want to be a victim, too!
Do not leave the victim unless there is
absolutely no other option. You should stay with the victim
while Emergency Medical Services (EMS) is contacted. The caller
should come back to you afterwards to verify that the call was
made. If the victim is not breathing, does not have a heartbeat,
or is badly injured, quick response by a team of emergency
medical technicians (EMT's) or paramedics gives the best chance
for survival.
Learn first aid and CPR now!
Once you know that electrical current is no
longer flowing through the victim, call out to the victim to see
if he or she is conscious (awake). If the victim is conscious,
tell the victim not to move. It is possible for a shock victim
to be seriously injured but not realize it. Quickly examine the
victim for signs of major bleeding. If there is a lot of
bleeding, place a cloth (such as a handkerchief or bandanna)
over the wound and apply pressure. If the wound is in an arm or
leg and keeps bleeding a lot, gently elevate the injured area
while keeping pressure on the wound. Keep the victim warm and
talk to him or her until help arrives.
If the victim is unconscious, check for signs of
breathing. While you do this, move the victim as little as
possible. If the victim is not breathing, someone trained in CPR
should begin artificial breathing, then check to see if the
victim has a pulse. Quick action is essential! To be effective,
CPR must be performed within 4 minutes of the shock.
If you are not trained in CPR or first aid, now
is the time to get trained-before you find yourself in this
situation! Ask your instructor or supervisor how you can become
certified in CPR. You also need to know the location of (1)
electricity shut-offs ("kill switches"), (2) first-aid
sup-plies, and (3) a telephone so you can find them quickly in
an emergency.
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The best way to stay safe is leave electrical work to the pros here at
Advanced Electrical Services Inc. Philadelphia Pa. Electricians in
Philly Pa. 215-396-2804
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Electrical Fire Hazards Pictures & Dangerous wiring in Philadelphia Pa.
Call :
215-3962804
for Repairs in Philadelphia Pa.
More pictures to come . Updated 6/19/10
