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ELECTRICAL HAZARDS DEFINED
Electricity is the flow of negatively charged particles
(electrons) through electrically conductive material.
Electrons orbit the nucleus of an atom, located
approximately in the atom’s
atom s center.
center
The negative charge of electrons
is neutralized by particles called
neutrons, acting as temporary
energy repositories for the
interactions between positively
charged particles called protons
and electrons.
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ELECTRICAL HAZARDS DEFINED
Basic characteristics of a material are determined by the
number of electron rings and the number of electrons in
the outer rings of its atoms.
Each ring of electrons contains
a particular quantity of negative
charges.
ELECTRICAL HAZARDS DEFINED
A positive charge is present when an atom (or group of
atoms) has too many electrons in its outer shell.
In all other cases, the atom or material carries a
negative charge.
charge
Electrons freed from an atom
& directed by external forces
to travel in a specific direction
produce electrical current, also
called electricity.
electricity
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ELECTRICAL HAZARDS DEFINED
Conductors are materials with many free electrons at
room temperature, and can pass electricity.
Insulators do not have a large number of free electrons at
room temperature.
And do not conduct electricity.
Substances that are neither conductors nor insulators can
be called semiconductors.
ELECTRICAL HAZARDS DEFINED
Electrical current passing through the human body causes a
shock.
The quantity and path of this current determines the
level of damage to the body.
The path of this flow of electrons is from a negative source
to a positive point.
Because opposite charges attract one another.
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ELECTRICAL HAZARDS DEFINED
When a surplus or deficiency of electrons on the surface of
a material exists, static electricity is produced.
So-called because there is no positive material nearby
to attract the electrons and cause them to move.
When two surfaces of opposite static charges are brought to
close range, a discharge (spark) occurs.
ELECTRICAL HAZARDS DEFINED
The potential difference between two points in a circuit
is measured by voltage.
The higher the voltage, the more likely that electricity
will flow between negative & positive points.
points
• The higher the resistance—measured in ohms—the
lower the flow of electrons.
– Pure conductors offer little resistance to electron
flow.
– Insulators have veryy high
g resistance to electricity.
y
– Semiconductors have a medium-range resistance.
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ELECTRICAL HAZARDS DEFINED
The unit of measurement for electrical current is amperes
(amps)—usually designated by the letter I.
One amp is a current flow of
6.28 x 1018 electrons per second.
ELECTRICAL HAZARDS DEFINED
One ohm is the resistance of a conductor that has a
current of one amp under the potential of one volt.
Ohm’s law describes the relationship among volts,
ohms and amps,
ohms,
amps stated as:.
as:
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ELECTRICAL HAZARDS DEFINED
Power is measured in wattage (watts), and can be
determined from Ohm’s law:
ELECTRICAL HAZARDS DEFINED
Most industrial and domestic use of electricity is supplied
by alternating current (AC).
In the U.S., standard AC circuits cycle 60 times per
second called the frequency,
second,
frequency measured in hertz.
hertz
Because voltage cycles, effective current for AC
is slightly less than peak current during a cycle.
A direct current (DC current) has been found to
generate as much heat as a peak AC current 41.4%
percent higher.
Effective voltages are computed using
the same ratios as effective current.
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ELECTRICAL HAZARDS DEFINED
The path of electrical current must make a complete loop
for the current to flow.
This loop includes the source of electrical power, a
conductor to act as the path
path, a device to use the
current (called a load), and a path to the ground.
The earth is considered to have zero potential because of
its massive size—an electrical conductor pushed into the
earth is said to have zero potential.
Electrocution occurs when a person makes contact with a
conductor
d
carrying
i a current & simultaneously
i l
l contacts
the ground, or another object that includes a conductive
path to the ground.
ELECTRICAL HAZARDS DEFINED
Typical 110-volt circuit wiring has a hot wire carrying
current, a neutral wire, and a ground wire.
The neutral wire may be called a grounded
conductor with the ground wire being called a
conductor,
grounding conductor.
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ELECTRICAL HAZARDS DEFINED
The hot wire carries effective voltage of 110 volts, the
neutral wire carries nearly zero voltage.
If the hot wire makes contact with an unintended
conductor the current can bypass the load & go
conductor,
directly to the ground.
ELECTRICAL HAZARDS DEFINED
A short circuit is a circuit in which the load has
been removed or bypassed.
The ground wire in a standard three-wire circuit
provides a direct path to the ground
ground, bypassing the
load.
• Short circuits can be an electrical hazard if a
human is the conductor to the ground, thereby
bypassing the load.
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SOURCES OF ELECTRICAL HAZARDS
The major causes of electrical shock are:
Contact with a bare wire carrying current.
Working with electrical equipment that lacks the UL
label for safety inspection.
Electrical equipment not been properly grounded.
Working with electrical equipment on damp floors or
other sources of wetness.
Static electricity discharge.
U i metall lladders
Using
dd
to work
k on electrical
l
i l equipment.
i
Working on electrical equipment without ensuring that
the power has been shut off.
Lightning strikes.
SOURCES OF ELECTRICAL HAZARDS
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Electrostatic Hazards
Shocks from static electricity may result from a single
discharge or multiple discharges of static.
Sources of electrostatic discharge include:
Briskly rubbing a nonconductive material over a
stationary surface.
Multilayered clothing may also cause static sparks.
Moving large sheets of plastic, which may discharge
sparks.
Static buildup in farm grain silos and mine shafts.
shafts
Conveyor belts may cause static sparks.
Vehicle tires rolling across a road surface.
Friction between a flowing liquid and a solid surface.
Arcs and Sparks Hazards
With close proximity, or contact of conductors to complete
a circuit, an electric arc can jump the air gap between the
conductors, and ignite combustible gases or dusts.
A spark or arc may involve relatively little or a great deal
of power and is usually discharged into a small space.
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Combustible and Explosive Materials
High currents through contaminated liquids may cause
contaminants to expand rapidly and explode.
Particularly dangerous with contaminated oil-filled
circuit breakers or transformers.
A poor match between current or polarity and capacitors
can cause an explosion.
Overheating from high currents can also lead to short
circuits, which may generate fires/explosions.
Lightning Hazards
Lightning is static charges from clouds following the path of
least resistance to the earth, involving very high voltage
and current.
If this path to the earth involves humans, serious
disability may result, including electrocution.
Lightning tends to strike the tallest object on the earth
below the clouds.
A tree is a common natural path for lightning.
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Improper Wiring
Improper wiring permits equipment to operate normally
but can result in hazardous conditions.
One common mistake is to “jump” the ground wire to the
neutral wire.
The ground wire is actually connected to the neutral
wire.
If the neutral circuit becomes corroded or loose, the ground
wire voltage increases to a dangerous level.
When the ground is connected improperly,
improperly the situation is
referred to as open ground.
Improper Wiring
With reversed polarity, the hot and neutral wires have
been reversed.
A worker unaware that the black (hot) & white (neutral)
leads have been reversed could be injured.
injured
If a short between the on/off switch and the load occurs,
equipment may run indefinitely, despite switch
position.
In a reversed polarity light bulb socket, the screw threads
become conductors.
• Flexible wiring should rarely be substituted for fixed wiring
in permanent buildings.
– A loose knot should be tied in a flexible cord when the
plug is installed or replaced to prevent a pull on the cord
from being transmitted to electrical connections.
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Insulation Failure
Causes of insulation failure:
Direct sunlight or other sources of ultraviolet light.
Sparks or arcs from discharging static electricity, which can
result in burned-through holes in insulation.
Repeated exposure to elevated temperatures, producing slow
but progressive degradation of insulation material.
Abrasive surfaces can result in erosion of the insulation.
Substance incompatibility with the atmosphere around
the insulation, which can induce chemical reactions.
Animals such as rodents or insects chewing or eating the
insulation material, leading to exposure of the circuit.
• Insects can pack an enclosed area tightly that a short
occurs.
Moisture & humidity absorbed by the insulation material.
Equipment Failure
Common types of equipment failure:
Wet insulation can become a conductor and cause an
electrical shock.
Portable tool defects can result in the device’s housing
carrying an electric current.
Broken power lines carry great amperage & voltage and
can cause severe disability.
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Hazardous Locations for Electrical Equipment
NEC hazardous locations for electrical equipment.
ELECTRICAL HAZARDS TO HUMANS
The greatest danger to humans suffering electrical shock
results from current flow.
Some levels of current “freeze” a person to the
conductor; the person cannot voluntarily release his
or her grasp.
Let-go current is the highest current level at which a
person in contact with the conductor can release the
grasp of the conductor.
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ELECTRICAL HAZARDS TO HUMANS
Severity of injury depends on
the dosage of current, and the
path taken through the body
b th
by
the current.
t
The path is influenced by
resistance of various body
parts at the time of contact.
Skin is the major form of
resistance to current flow.
Current paths through the
h
heart,
b
brain,
i or trunk
k are
generally much more
injurious than paths
through extremities.
DETECTION OF ELECTRICAL HAZARDS
A circuit tester is an inexpensive piece of equipment with
two wire leads capped by probes, connected to a small
bulb—most test at least 110- to 220-volts.
The tester can ensure power has been turned off and
determine whether housings & other equipment parts
are carrying a current.
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DETECTION OF ELECTRICAL HAZARDS
A receptacle wiring tester is a device with two
standard plug probes for insertion into an ordinary 110volt outlet and a probe for the ground.
Indicator lights show an improperly wired receptacle
(outlet).
DETECTION OF ELECTRICAL HAZARDS
A continuity tester may be used to determine whether a
conductor is properly grounded or has a break in the
circuit.
Continuity is checked on circuits that are disconnected
from a power source.
• One terminal of the tester can be connected to the
equipment housing; the other terminal is connected to a
known ground.
– If the bulb does not light, the equipment is shown to be
improperly grounded.
– With a circuit, the bulb lights when a current is capable
of passing through the complete circuit.
– An unlit bulb of indicates a break in the circuit.
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REDUCTION OF ELECTRICAL HAZARDS
The purpose of grounding is to safeguard people from
electrical shocks, reduce the probability of a fire, and
protect equipment from damage.
Grounding ensures a path to the earth for the flow of
excess current.
Grounding also eliminates the possibility of a person
being shocked by contact with a charged capacitor.
Power surges and voltage changes are attenuated
proper
p system
y
g
grounding.
g
and usuallyy eliminated with p
REDUCTION OF ELECTRICAL HAZARDS
Bonding—used to connect two pieces of equipment by a
conductor—can reduce potential differences between the
equipment & reduce sparking.
Bonding and grounding together are used for entire
electrical systems.
Separate equipment grounding involves connecting all metal
frames of the equipment in a permanent and continuous
manner.
If an insulation failure occurs, the current should return
to the
h system ground
d at the
h power supply
l ffor the
h circuit.
i i
• The equipment ground wiring will be the path for the
circuit current, enabling circuit breakers and fuses to
operate properly.
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REDUCTION OF ELECTRICAL HAZARDS
The exposed metal parts of the equipment
shown must be g
grounded or double insulated
REDUCTION OF ELECTRICAL HAZARDS
A ground fault circuit interrupter (GFCI) can detect
the flow of current to ground & open the circuit, thereby
interrupting the flow of current.
When the current flow in the hot wire is greater than the
current in the neutral wire, a ground fault has
occurred.
The GFI cannot interrupt current passing between two
circuits or between the hot and neutral wires of a threewire circuit.
A GFI should be replaced periodically based on the
manufacturer’s recommendations.
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REDUCTION OF ELECTRICAL HAZARDS
The primary hazard of static electricity is the transfer of
charges to surfaces with lower potential.
Bonding and grounding are two means of controlling
static.
• Humidification above 65% is a mechanism for
reducing static.
Antistatic materials reduce electrical static hazards.
Increasing surface conductivity, reducing resistance.
Ionizers & electrostatic neutralizers ionize air around a
charged surface, to provide a conductive path for flow of
charges.
Radioactive neutralizers include a emit positive particles
to neutralize collected negative electrical charges.
REDUCTION OF ELECTRICAL HAZARDS
Fuses consist of a metal strip or wire that melts if a
current above a specific value passes through it.
This causes the circuit to open, stopping current flow.
Magnetic
i circuit
i
i breakers
b
k
use a solenoid
l
id to surround
da
metal strip connected to a tripping device.
When allowable current is exceeded, the magnetic force
of the solenoid retracts the metal strip, opening the
circuit.
Thermal circuit breakers rely on excess current to
produce heat and bending in a sensitive metal strip.
Once bent, the metal strip opens the circuit.
Circuit breakers are usually easier to reset than fuses &
often provide a lower time lag or none at all.
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REDUCTION OF ELECTRICAL HAZARDS
There are numerous methods of reducing
the risk of electrocution by lightning.
REDUCTION OF ELECTRICAL HAZARDS
Some of the
many methods
of reducing
electrical
hazards
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OSHA’S ELECTRICAL STANDARDS
OSHA standards relating to electricity are found in 29 CFR
1910 (Subpart S), extracted from the NEC.
The NEC code should be referred to when more detail
is needed than appears in OSHA
OSHA’ss excerpts.
excerpts
• Subpart S is divided into two categories of standards:
– Design of Electrical Systems.
– Safety-Related Work Practices.
ELECTRICAL SAFETY PROGRAM
Some NIOSH strategies for establishing an electrical safety
program:
Develop & implement a comprehensive safety program, revise
when necessary & comply with OSHA regulations.
regulations
Provide all workers with training in identification & control of
hazards associated with electricity in their workplace.
• Provide periodic retraining as necessary
Provide additional specialized training to those working with or
around exposed electric circuit component.
• Basic
as c electrical
e ect ca theory,
t eo y, safe
sa e work
o p
procedures,
ocedu es, hazard
a a d
awareness & identification, proper use of PPE,
lockout/tagout, first aid including CPR, and proper rescue
procedures.
Conduct safety meetings, and scheduled & unscheduled safety
inspections at work sites
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ELECTRICAL SAFETY PROGRAM
Some NIOSH strategies for establishing an electrical
safety program:
– Develop/implement procedures to control hazardous
electrical
l t i l energy th
thatt iinclude
l d llockout/tagout
k t/t
t procedures.
d
• Ensure that workers follow these procedures.
– Provide testing/detection equipment for those who work
directly with electrical energy that ensure their safety.
– Ensure that proper PPE is available and worn by workers
where required (including fall protection equipment).
– Conduct
C d t job
j bh
hazard
d analyses
l
off all
ll ttasks
k and
d iimplement
l
t
measures to insulate/isolate workers from electricity.
– Identify potential hazards &appropriate safety
interventions during the planning phase of construction or
maintenance.
ELECTRICAL HAZARDS SELF-ASSESSMENT
To help prevent accidents & injuries from electrical
hazards, safety personnel should consider check-lists
supervisors can use for assessments in their areas of
responsibility.
ibili
Are all electricians in your company up-to-date with
the latest requirements of the NEC?
Does your company specify compliance with the NEC
as part of its contracts for electrical work with
outside personnel?
Do all electrical installations located in the presence
of hazardous dust or vapors meet NEC requirements
for hazardous locations?
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ELECTRICAL HAZARDS SELF-ASSESSMENT
• Check-list items for supervisors:
Are all electrical cords properly strung, unfrayed, and free of
grease, oil, chemicals & other damaging materials?
Are all portable electric tools & appliances grounded or double
insulated?
Is all conduit, BX cable, etc., properly attached to supports
and tightly connected to junction boxes and outlet boxes?
Are metallic cables & conduit systems properly grounded?
Are all ground connections clean and tightly made?
Are all fuses & circuit breakers the proper size/type for the
load on each circuit, and free of “jumping”
Are all electrical switches properly marked to show their
purpose, properly mounted in clean, tightly closed metal
boxes, and free of evidence of overheating?
ELECTRICAL HAZARDS SELF-ASSESSMENT
• Check-list items for supervisors:
Are all electric motors kept clean and free of excessive
grease, oil, or potentially damaging materials?
A all
Are
ll electric
l t i motors
t
properly
l maintained
i t i d and
d provided
id d
with the necessary level of overcurrent protection?
Are bearings in all electrical motors in good condition?
Are all portable lights equipped with the proper guards?
Are all lamps kept free of any potentially combustible
materials?
I the
Is
th organization’s
i ti ’ overall
ll electrical
l t i l system
t
periodically
i di ll
checked by a person competent in the application of the
NEC?
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PREVENTION OF ARC FLASH INJURIES
An arc flash is an electrical short-circuit that travels
through air rather than flowing through conductors, bus
bars, and other types of equipment.
The uncontrolled energy released by an arc flash can
produce high levels of heat and pressure.
• It can also cause equipment to explode, sending
dangerous shrapnel flying through the air.
Arc flashes are sometimes produced by equipment
malfunctions,, but a more common cause is human
contact with an electrical circuit or conductor.
Arc flashes can ignite clothing, cause severe burns, and
even damage hearing by the high level of pressure that
can be released by an arc flash.
PREVENTION OF ARC FLASH INJURIES
The best, most obvious way to prevent arc flash injuries is
to de-energize the equipment and lock or tag it out
before beginning work on it.
Some maintenance/service functions, such as
troubleshooting require the equipment be energized.
When this is the case, consult NFPA’s Handbook for
Electrical Safety in the Workplace (NFPA 70E).
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TRAINING REQUIREMENTS FOR WORKERS
OSHA training requirements for all workers are contained
in 29 CFR 1910, and include:
Skills and techniques necessary to distinguish exposed
live parts from other parts of electric equipment.
Skills and techniques necessary to determine the
nominal voltage of exposed live parts.
Clearance distances and corresponding voltages to
which they will be exposed.
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