Ninety-nine percent of what you do in your job as a
Fire Controlman , you will do around electricity. Since
that makes you extremely susceptible to electric shock,
its very important for you to know the basics of
electric shock, how to avoid being shocked, and how to
treat victims of electric shock. The following section
discusses those factors.
This section discusses the severity, avoidance, and
victims of electric shock.
BASICS OF ELECTRIC SHOCK
The following factors determine the severity of the
effect electric shock has on your body:
The amount of body resistance you have to the
The path the current takes through your body.
The length of time the current flows through
Resistance varies greatly in different parts of your
body. A value of 1,500 ohms is commonly used as the
resistance between major extremities of an average
human body: hand to hand, or hand to foot.
For example, suppose you accidentally grabbed a
wire carrying 120 volts alternating current (V ac). We
can use Ohms law, I = E/R, to figure how much current
would flow through your body:
E = 120 V ac (the voltage you grabbed)
R = 1,500 ohms (your average body resistance)
I = 120/1,500 amp
I = .080 amp
I = 80 milliamperes
Therefore, if you grabbed a 120-V-ac wire, 80
milliamperes of current would flow through your
Table 3-1 shows the effects of varying amounts of
electric shock on a normal person. In our example, you
grabbed 80 milliamperes of current!
That is 15
milliamperes beyond what could be fatal. It is also 70
milliamperes beyond the cant-let-go threshold for a
120-pound person and 62 milliamperes beyond what is
needed to cause you to stop breathing.
Remember, the 1,500 ohms is just an average
value. Body resistance varies from person to person
and may often be less than 1,500 ohms. When your
skin is moist, your body resistance could be as low as
300 ohms! Also, breaks in your skin at the point of
contact could reduce your skin resistance to nearly
Skin resistance is only important when you are
handling voltages of less than 240 volts. If you get
shocked by more than 240 volts, the voltage arc will
burn through your skin and leave deep, third-degree
burns where it enters your body.
Current Flow Path
The two most dangerous paths that current can take
through your body are (1) from hand to hand and (2)
from left hand to either foot. The second path is the
MOST dangerous since the current will flow through
both your heart and other vital organs.
Current Flow Duration
Fibrillation is the shocking of your heart into a
useless flutter. The longer you are shocked, the more
chance there is for your heart to begin fibrillating. Most
people who die from electric shock die from
fibrillation. Fibrillation in a normal adult is unlikely if
the current in milliamperes is less than 116/t, where t
is the shock duration in seconds. The longer you are
shocked, the less current is needed to cause heart
(at 60 Hertz)
PERCEPTION: A slight tingling
CANT LET GO: Arm and hand
muscles close involuntarily:
A 120-pound person.
A 175-pound person.
CANT BREATHE: PARALYSIS OF
THE CHEST MUSCLES.
HEART FIBRILLATION: Rapid,
irregular contractions of the heart
muscles. Could be fatal.
Table 3-1.Effects of Electric Shock