#import "../../core/core.typ"

=== Common sources of hazard

Of course there is danger of electrical shock when directly performing
manual work on an electrical power system. However, electric shock
hazards exist in many other places, thanks to the widespread use of
electric power in our lives.

As we saw earlier, skin and body resistance has a lot to do with the
relative hazard of electric circuits. The higher the body\'s resistance,
the less likely harmful current will result from any given amount of
voltage. Conversely, the lower the body\'s resistance, the more likely
for injury to occur from the application of a voltage.

The easiest way to decrease skin resistance is to get it wet. Therefore,
touching electrical devices with wet hands, wet feet, or especially in a
sweaty condition (salt water is a much better conductor of electricity
than fresh water) is dangerous. In the household, the bathroom is one of
the more likely places where wet people may contact electrical
appliances, and so shock hazard is a definite threat there. Good
bathroom design will locate power receptacles away from bathtubs,
showers, and sinks to discourage the use of appliances nearby.
Telephones that plug into a wall socket are also sources of hazardous
voltage (the open circuit voltage is 48 volts DC, and the ringing signal
is 150 volts AC -- remember that any voltage over 30 is considered
potentially dangerous!). Appliances such as telephones and radios should
never, ever be used while sitting in a bathtub. Even battery-powered
devices should be avoided. Some battery-operated devices employ
voltage-increasing circuitry capable of generating lethal potentials.

Swimming pools are another source of trouble, since people often operate
radios and other powered appliances nearby. The National Electrical Code
requires that special shock-detecting receptacles called Ground-Fault
Current Interrupting (GFI or GFCI) be installed in wet and outdoor areas
to help prevent shock incidents. More on these devices in a later
section of this chapter. These special devices have no doubt saved many
lives, but they can be no substitute for common sense and diligent
precaution. As with firearms, the best \"safety\" is an informed and
conscientious operator.

Extension cords, so commonly used at home and in industry, are also
sources of potential hazard. All cords should be regularly inspected for
abrasion or cracking of insulation, and repaired immediately. One sure
method of removing a damaged cord from service is to unplug it from the
receptacle, then cut off that plug (the \"male\" plug) with a pair of
side-cutting pliers to ensure that no one can use it until it is fixed.
This is important on jobsites, where many people share the same
equipment, and not all people there may be aware of the hazards.

Any power tool showing evidence of electrical problems should be
immediately serviced as well. I\'ve heard several horror stories of
people who continue to work with hand tools that periodically shock
them. Remember, #emph[electricity can kill], and the death it brings can
be gruesome. Like extension cords, a bad power tool can be removed from
service by unplugging it and cutting off the plug at the end of the
cord.

Downed power lines are an obvious source of electric shock hazard and
should be avoided at all costs. The voltages present between power lines
or between a power line and earth ground are typically very high (2400
volts being one of the lowest voltages used in residential distribution
systems). If a power line is broken and the metal conductor falls to the
ground, the immediate result will usually be a tremendous amount of
arcing (sparks produced), often enough to dislodge chunks of concrete or
asphalt from the road surface, and reports rivaling that of a rifle or
shotgun. To come into direct contact with a downed power line is almost
sure to cause death, but other hazards exist which are not so obvious.

When a line touches the ground, current travels between that downed
conductor and the nearest grounding point in the system, thus
establishing a circuit:

#image("static/00067.png")

The earth, being a conductor (if only a poor one), will conduct current
between the downed line and the nearest system ground point, which will
be some kind of conductor buried in the ground for good contact. Being
that the earth is a much poorer conductor of electricity than the metal
cables strung along the power poles, there will be substantial voltage
dropped between the point of cable contact with the ground and the
grounding conductor, and little voltage dropped along the length of the
cabling (the following figures are #emph[very] approximate):

#image("static/00068.png")

If the distance between the two ground contact points (the downed cable
and the system ground) is small, there will be substantial voltage
dropped along short distances between the two points. Therefore, a
person standing on the ground between those two points will be in danger
of receiving an electric shock by intercepting a voltage between their
two feet!

#image("static/00069.png")

Again, these voltage figures are very approximate, but they serve to
illustrate a potential hazard: that a person can become a victim of
electric shock from a downed power line without even coming into contact
with that line!

One practical precaution a person could take if they see a power line
falling towards the ground is to only contact the ground at one point,
either by running away (when you run, only one foot contacts the ground
at any given time), or if there\'s nowhere to run, by standing on one
foot. Obviously, if there\'s somewhere safer to run, running is the best
option. By eliminating two points of contact with the ground, there will
be no chance of applying deadly voltage across the body through both
legs.

#core.review[
  - Wet conditions increase risk of electric shock by lowering skin
    resistance.

  - Immediately replace worn or damaged extension cords and power tools.
    You can prevent innocent use of a bad cord or tool by cutting the male
    plug off the cord (while its unplugged from the receptacle, of
    course).

  - Power lines are very dangerous and should be avoided at all costs. If
    you see a line about to hit the ground, stand on one foot or run (only
    one foot contacting the ground) to prevent shock from voltage dropped
    across the ground between the line and the system ground point.
]
