Download Chapter 2: Electrical Hazards

Chapter 2: Electrical Hazards
Learning Objectives
In this chapter you will learn to:
• discuss the effects of electrical current on the human body;
• detect electrical hazards, determine which OSHA standards
apply, achieve the appropriate standards, and achieve the
appropriate protection; and
• discuss safe electrical work practices.
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True / False Quiz
This exercise shows how much you already know about electrical
hazards at construction renovation sites. It is not a test, and
scores will not be recorded. The only purpose of this quiz is to
give you an idea of what you need to learn to stay safe on the
job. Please take a few minutes to read the statements, then circle
T for “True” and F for “False.” Your instructor will go over the
answers when everyone in the class finishes the exercise.
1. When one of your co-workers is in contact with an
electrical circuit and being shocked, you should grab
him or her and break their connection with the electrical
current as quickly as possible. T F
2. All electricity is looking for ground. T F
3. Ground fault circuit interrupters (GFCI) should be used
at construction sites in addition to regular grounding and
insulation. T F
4. When you install temporary wiring at a construction site,
always disconnect it within the same workday. T F
5. Before working on electrical circuits, shut off all power at
the disconnect (i.e., circuit breaker or fusible switch) and
install a lockout/tagout system. T F
6. During renovations, you can plug your extension cords into
the existing building power outlets without any additional
equipment. T F
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Basics of Electricity
How serious a workplace hazard is electricity?
Very serious. Workers who misuse electricity may suffer injury
or death from electrical shock, electrocution, burns, fires and
explosions. In 1999 alone, 278 workers in this country died from
electrocutions on the job—or almost 5 percent of all recorded
U.S. workplace deaths. Most of these fatalities could have been
easily avoided. In addition, there are approximately 30,000
electrical shock accidents in this country each year.
How do different materials affect the flow of
electricity?
A “conductor” is a material that electricity flows through
easily. Conductors include metals, air, and even the earth itself.
“Insulator” materials slow or stop the flow of electricity and
include materials such as glass, plastic, porcelain, clay,
Many
pottery, and dry wood.
common
materials
Workers should avoid contact with known, uninsulated
can become
conductors of electricity and be careful in coming close
conductors
to supposedly poor conductors. Insulating materials can
of electricity.
become conductors in some cases. For example, pure
water is a poor conductor of electricity, but the addition of
small amounts of impurities in water, such as salt, acid, solvents
or other materials, can make water a conductor of electricity.
When insulating materials, such as dry wood or dry human skin,
become wet with water, they can become effective conductors of
electricity.
What causes electrical
shocks, and what hazards
do these pose?
+
Electricity travels in a defined
Source
path (or circuit), usually through
a conducting material. A person’s
body is a good conductor of
electricity and accidentally can
become a part of the circuit. When
this happens, the person may suffer an electrical shock.
Load
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Electrical shocks can affect the person in a variety of ways,
from a slight tingling sensation to a full heart attack. The most
common injury is electrical burns. The severity of a shock
Injury from
depends on the:
electricity
• amount of current passing through the person’s body;
depends on
current, path, • path the current takes through the body;
• length of time the body remains part of the electrical
and time.
circuit; and
• frequency of the current.
Depending upon the path that the current takes, if the shock
passes through the middle of the body, it may severely burn and
injure the internal organs.
Electrical shocks cause other hazards that also can injure people.
For example, electrical arcs can:
• start fires;
• send metal from damaged equipment flying in every
direction; and
• cause violent explosions that release toxic or flammable gases
into the air near workers.
Why do people “freeze” when they are shocked,
and what should their co-workers do to help them?
When people suffer from electrical shock, their muscles severely
tighten, and they often cannot break free from the electrical
circuit they are contacting. This situation is very dangerous,
because it increases the period of electrical shock. The longer a
person is exposed to a current, the greater the risk they face of
serious injury or death.
Act quickly, but
protect your
If a co-worker is “frozen” by contact with an electrical
own safety when circuit, shut off the electricity at once. If this is not
helping a victim
possible, pull or push the person away from the
of electrical
electrical source with boards, poles or sticks made of
shock.
wood or another non-conducting material. Do not
touch the person, or you may become part of the
circuit and be injured.
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Remember: you must act quickly to help a victim of electrical
shock, but protect your own safety by avoiding contact with the
electrical circuit through your endangered co-worker.
How do you know when a person has received a
severe electrical shock?
It is not always apparent. Shock victims suffer injuries that are
often not visible, including:
• severe burns and internal bleeding;
• tissue, nerve or muscle damage; and
• kidney and other organ damage.
A medical doctor should treat all victims of electrical shock.
What is static electricity, and why is it dangerous?
Static electricity occurs when a charge builds up on the surface of
an object. People can be shocked when they touch an object with
static and the electrical build-up is discharged. A good example
of a static electrical discharge is when a person grasps a metal
doorknob on a cold, dry day. In this case, the victim only suffers
minor discomfort, but static electrical discharges are often more
dangerous—for instance, when friction produces the build-up
of a high level of static electricity at a specific spot on an object
and the discharge ignites flammable or combustible substances
nearby.
This can occur when you fill up your truck on a cold, dry winter
day. If you do not ground yourself and the gas pump nozzle to
your gas port opening, a static discharge can occur and start a
fire. Static electricity can also occur when flammable liquids are
poured without properly bonding the containers together.
Static
This condition can cause fire and explosions.
discharge
will ignite
flammable
Basic Electrical Safety Work Practices
vapors.
Most electrical injuries happen because of unsafe equipment
or equipment installations, an unsafe environment, or
unsafe work practices. You can protect yourself and others from
such accidents with insulation, guarding, grounding, electrical
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protective devices, and safe work practices. Let’s discuss some of
the basic electrical safe work practices.
What are general safety guidelines to follow when
you’re working on or near electrical hazards?
You must receive training and be qualified to work on electrical
circuits. Unqualified workers should stay away from live electrical
wiring.
• Before starting work, find (or ask your employer to find)
any exposed or concealed hot electric power circuits on your
work site. If you are digging, operating a jack hammer, or
performing demo work, always wear appropriate voltage rated
gloves until you know the exact location of utilities. Always
call before you dig!
Know and • Your employer must determine if you
ONare qualified
use safe
through training and experience to work on or near hot
electrical
electrical equipment. It is up to your employer to decide if
work
you are qualified to do the work.
practices!
• The most important step that you can take to protect
yourself is to turn off all electrically powered equipment.
• All equipment should be locked and tagged out. To do a
lockout and tagout, an authorized person must locate the
switch or circuit breaker, shut off all power, and install a
lockout device with a tag to identify the person that put on
the lock. All locks must be used withOFF
tags.
• Never assume that electrical
equipment has been disconnected.
You must always act as if all electric
circuits are hot until a qualified person
makes sure that the energy has been
disconnected.
DANGER
• Remove all conductive clothing and
jewelry such as rings, watches, wrist
DO NOT
OPERATE
and neck chains, metal buttons, and
metal writing pens. Do not wear
synthetic fiber clothing (polyester or
other material) because electricity can
melt it.
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• Use recommended personal protective
equipment, shields, and/or barriers
that insulate you from contact with
electric circuits. These items include
electrically (voltage) rated insulated
gloves, aprons, eye protection such as
safety glasses and face shields, rubbersoled shoes, insulated shields, and
insulated tools.
• Avoid working in poorly lit areas where hot electric
equipment is located. If you must work in these areas, use
supplemental lighting.
Maintain
• Do not reach into areas with exposed electric
all
components if your view is partially or fully obstructed.
electrical
Make sure you have sufficient light to see in and around
tools and
any electrical components or equipment.
equipment
• Do not enter a confined space with exposed electric
in safe
parts, unless you’re qualified, authorized and wearing
condition
adequately rated protective clothing or are using proper
and check
barriers, shields or equipment.
them
• Do not use areas where exposed electrical equipment is
regularly
kept as shortcuts or passageways.
for defects.
• Make sure that ladders, scaffolds, or any other
equipment and materials that you use on the job never come
within 10 feet of an overhead electric high voltage power
line. If working at heights or handling long objects, make
sure there aren’t any overhead
wires close enough to touch
by accident. Know the voltage
of any power lines on your
project. You may be required
to stay more than 10 feet away
depending on the voltage.
This includes working in
equipment such as scissors lifts
and aerial lifts or on scaffolds
or any other raised platform.
• Do not bypass any protective
system or device designed
to protect employees from
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contact with
electricity. Do
not enter any
barricaded
electrical hazard
area unless you
are authorized
to do so.
Make sure
•
If an there is an electrical fire, use a Class C fire
ladders,
extinguisher to fight the fire.
scaffolds, or
equipment
never come
What are some key guidelines to follow in
within 10
using power tools?
feet of a
• Always have any underground utility, especially
power line.
underground electrical services properly located.
• Always wear insulated protective gloves when using
jackhammers or hand tools if the location of underground
power lines is unknown. If you are using these type insulated
gloves, they must be inspected prior to each use
and must also be tested at least twice each year
to ensure that they are providing the proper
insulation. (This is not something you, a worker,
does; your employer will send the gloves to a testing
laboratory qualified to do this.)
• Do not use any frayed, worn or otherwise defective
electrical cords or cables.
• Use only hard duty or extra hard duty 3-wire type
extension cords. You can identify 3-wire cords by the
lettering usually found on them: S, ST, SO, STO, SJ, SJT,
SJO, or SJTO.
• Maintain all electrical tools and equipment in safe
condition and check them regularly for defects.
• Tag any defective electrical equipment “Defective—Do Not
Use” or remove the tool from the site.
• Do not store electrical conductors or equipment in damp
or wet conditions; locations exposed to gases, fumes, vapors,
liquids or over corroding agents; or locations where they are
exposed to high temperatures.
• Never carry a tool by the cord or hose. This can cause the
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•
•
•
•
•
•
electrical insulation to pull away from the equipment and
expose the conductor wires.
Never yank the cord or hose to disconnect it from the
receptacle.
Disconnect or unplug tools when they are not in use, before
servicing, and when changing implements such as
Inspect
blades, bits and cutters.
power and
Wear insulated gloves and safety footwear when using
extension
tools.
cords
Check all of your electrical power tools to ensure that
frequently.
they are either three wire grounded or double insulated.
If they are double insulated, it will be marked on the
equipment.
Remove broken or damaged tools and equipment from the
job site.
Ensure that all electrical panels, generators, and welders
are properly grounded and also located so that will not be
exposed to rising water.
Insulation and Grounding
How do you identify the kind of insulation on an
electric wire?
Electrical wires are insulated by coating them with a
nonconductive material such as plastic. You can often identify
insulation by the color of the wire’s covering such as:
Be familiar
• green or green with yellow strips (or bare copper wire) for with the
color code
grounding conductors;
for the
• white or gray for grounded conductors; and
wiring on
• black or red for ungrounded conductors (though they can
each job.
be any color except green, white or gray).
Although these are the correct colors for these type wires, do
not assume that the colors are always correct on all equipment.
Always check insulation for any exposed wires before connecting
electrical equipment to a power source.
Why is it important to ground electrical equipment
and metal housings or enclosures?
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Grounding wires provide a path for siphoning off buildups
of excess electrical current from equipment and directing this
electricity safely into the earth. For example, a grounding wire
may run from electrical equipment to a known ground such as
a cold water pipe or a copper rod drove driven into the ground.
Electricity is always looking for ground.
Different grounding wires have different purposes: a service or
system ground primarily protects machines, tools and insulation.
An equipment grounding wire is designed to protect equipment
operators. Make sure that the ground wire is sufficient in size to
provide a proper ground.
What are the limitations of insulation and
grounding?
Insulation may be damaged by aging, heavy usage, or abuse of the
equipment. If workers aren’t observant, they may become exposed
to electrical shocks, burns or fires when working with wires they
think are well insulated. Double insulation can provide additional
protection, but it cannot protect against defective cords and plugs
or against very moist operating conditions.
Grounding reduces the chances of a serious electrical injury, but
it doesn’t guarantee that workers won’t get shocked. Users may
not know when a grounding system is malfunctioning.
A qualified worker should test all newly installed receptacles to
ensure the equipment is properly wired. If the receptacle was not
wired properly, you may create dangerous conditions such as an
open ground. The user of the equipment may think the receptacle
is grounded, but the ground wire may not be hooked up in the
circuit.
Proper grounding condition can be checking with a simple,
inexpensive circuit tester than can be purchased at any hardware
or construction materials supplier. If one isn’t available on the job
site, ask your employer for one. You must be trained and qualified
to test electrical circuits.
In what cases is it important to use ground fault
circuit interrupters?
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Insulation and grounding usually provide protection from
electrical-related injuries, but these methods do not solve all
problems. On construction sites,
common residential circuit breakers
do not provide enough protection to
prevent injuries. Circuit breakers work
when the electrical current flowing
is too great due to fault causing the
RESET
breaker to “heat up” and the breaker
TEST
to “open.” A ground fault circuit
interrupter (GFCI) works differently
by measuring whether there’s a
dangerous situation by comparing the
amount of electrical current going into
equipment with the amount of current
returning from it. If the difference is
too great, then the device automatically trips a circuit breaker or
blows a fuse, shutting off power. Because of this design, GFCIs
are fast-acting circuit breakers which can interrupt the flow of
electricity in as little as 1/40 of a second. Use GFCI devices
for all construction site equipment. If you are plugging into the
existing buildings’ power (not equipped with GFCI)
Use GFCI’s
you must use a GFCI cord set (commonly referred to
on all jobs.
as a “pigtail” or a temporary GFCI device) between
It could save
the existing power and your equipment. Always plug
your life!
the pigtail into the outlet before your extension card or
equipment plug. Do not plug the pigtail into the user
end of the extension cord!
All temporary 120 volt, 15 and 20 amp receptacles must be
protected by a ground fault circuit interrupter. You may plug
the power cord of your tool directly into an existing permanent
receptacle on the construction site, if you are not in a wet or
damp location. It is a best practice to always use ground fault
circuit interrupters.
Electrical Requirements: Portable Equipment
What must you do to protect your safety while
running portable equipment?
Construction workers frequently use portable tools, which
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require flexible extension cords. As a general rule, flexible cords
are easier to damage than fixed wiring because they are often
stretched, twisted and yanked.
To protect workplace safety, you must inspect the tools before
each day of use to ensure the cord and plug are not damaged. If
the tool is damaged, take it out of service immediately by tagging
it and putting in a secured location. On construction sites, the
insulation of cords is sometimes cracked or torn away, exposing
workers to hot electricity. These electrical currents often are
strong enough that workers shocked by them may fall or suffer
other potentially fatal injuries.
All portable tools must either be grounded or double insulated.
Double insulated tools have their electrical parts isolated from
the tool case. They typically have either a symbol or will show
that double insulation is present on the equipment.
Portable tools and the cords connecting them to power sources
should be protected with ground fault circuit interrupters
(GFCIs)—grounding devices that trip circuits very rapidly when
they detect dangerous electric discharges.
Double insulation symbol
Temporary Wiring Requirements
What are the general requirements for temporary
wiring?
Temporary wiring is often necessary on construction sites. Here
are some important safety guidelines to follow:
• use GFCI devices on all temporary power sources (including
extension cords);
• choose only grounding-type receptacles;
• ground metal-case sockets;
• never suspend temporary lights by their electric cords unless
cords and lights are designed for this means of suspension;
and
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• remove temporary wiring immediately after completion
of construction or the purpose for which the wiring was
installed.
Portable Generators
What are the electrical hazards of power
generators?
During power loss or until temporary power is established, it is a
common practice to produce electricity with portable generators.
Before starting any generator, make sure to turn off the main
circuit breaker and lock it out. Otherwise, power lines may
become re-energized (hot) with electricity inadvertently back-fed
from the generator. In these cases, utility workers face possible
electrocution while they work on power lines.
Always ensure that temporary generators are properly grounded
with a proper ground strap attached to a proper ground source.
Additionally, always ensure that the generator is equipped with
GFCI or that you use a pigtail at the generator plug-in.
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Key Terms to Remember
Here are some of the key terms presented in this chapter. Let’s
review them one more time to reinforce the lessons you learned
about electrical hazards.
Conductor: A “conductor” is a material that electricity flows
through easily. Conductors include metals, air, and even the earth
itself. “Insulator” materials slow or stop the flow of electricity and
include materials such as glass, plastic, porcelain, clay, pottery,
and dry wood.
Electrical circuit: A defined path that electricity follows, usually
passing through a conducting material. A person’s body is a good
conductor of electricity and accidentally can become a part of the
circuit.
Electrical shock: An injury that occurs when a person become
a part of the circuit. Electrical shocks can affect the person in a
variety of ways, from a slight tingling sensation to full cardiac
arrest. The most common injury is electrical burns.
Ground fault circuit interrupter (GFCI): GFCIs are fastacting circuit breakers, which can interrupt the flow of electricity
in as little as 1/40 of a second.
GFCI cord set: A cord with an inline ground fault circuit
interrupter. Commonly referred to as a “pigtail.”
Grounding: A technique that provides a path (through a
grounding wire) for siphoning off buildups of excess electrical
current from equipment and directing this electricity safely into
the earth.
Insulator: “Insulator” materials slow or stop the flow of
electricity and include materials such as glass, plastic, porcelain,
clay, pottery, and dry wood.
Pigtail: see GFCI cord set
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Lockout/tagout: This technique helps
safeguard employees from hazardous energy,
such as electricity while they are performing
service or maintenance on machines and
equipment. A lockout device is an energyisolating device that ensures the equipment it
controls cannot be operated until the lockout
device is removed. A tagout device indicates
that equipment being controlled may not be
operated until the tagout device is removed.
ON
OFF
DANGER
DO NOT
OPERATE
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True / False Quiz Revisited
Here are the answers to the pre-chapter quiz. How did you do?
1.
A Type C fire extinguisher is the type that works on
electrical fires. True
If an there is an electrical fire, use a Type C fire extinguisher.
2.
When one of your co-workers is in contact with an
electrical circuit and being shocked, you should grab him or
her and break their connection with the electrical current as
quickly as possible. False
If a co-worker is “frozen” by contact with an electrical circuit, shut
off the electricity at once. If this is not possible, pull or push the
person away from the electrical source with boards, poles or sticks
made of wood or another non-conducting material. Do not touch
the person or you may become part of the circuit and be injured.
3.
All electricity is looking for ground. True
4.
Ground fault circuit interrupters (GFCI) should be used
at construction sites in addition to regular grounding and
insulation. True
Grounding wires provide a path for siphoning off buildups of excess
electrical current from equipment and directing this electricity
safely into the earth. For example, a grounding wire may run from
electrical equipment to a known ground such as a cold water pipe
or a copper rod drove driven into the ground. Electricity is always
looking for ground.
A ground fault circuit interrupter (GFCI) works differently by
measuring whether there’s a dangerous situation by comparing the
amount of electrical current going into equipment with the amount
of current returning from it. If the difference is too great, then the
device automatically trips a circuit breaker or blows a fuse, shutting
off power. Because of this design, GFCIs are fast-acting circuit
breakers which can interrupt the flow of electricity in as little as
1/40 of a second. Use ground fault circuit interrupter (GFCI)
devices for all construction site equipment.
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5.
When you install temporary wiring at a construction site,
always disconnect it within the same workday. False
Remove temporary wiring immediately after completion of
construction or the purpose for which the wiring was installed.
6.
Before working on electrical circuits, shut off all power at
the disconnect (i.e., circuit breaker or fusible switch) and
install a lockout/tagout system. True
The most important step that you can take to protect yourself is to
turn off all electrically powered equipment. All equipment should be
locked and tagged out. To do a lock out and tagout, an authorized
person must locate the switch or circuit breaker, shut off all power,
and install a lockout device with a tag to identify the person that
put on the lock. All locks must be used with tags.
7.
During renovations, you can plug your extension cords into
the existing building power outlets without any additional
equipment. False
Use ground fault circuit interrupter (GFCI) devices for all
construction site equipment. If you are plugging into the existing
buildings’ power (not equipped with GFCI) you must use a GFCI
cord set (commonly referred to as a “pigtail” or a temporary GFCI
device) between the existing power and your equipment.
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