This document discusses electrical hazards and how to prevent them. It describes the dangers of electricity like electric shock, burns, falls and fires. Two main types of electrical injuries are direct injuries from electrocution or shock and indirect injuries from falls. Common electrical hazards on construction sites include high-voltage overhead power lines, inadequate wiring, damaged cords and wires, improper grounding, and overloaded circuits. The document provides tips for controlling hazards through proper grounding, GFCI use, avoiding wet conditions and following safe work practices.

1. Electrical Hazards
AND
PREVENTION

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Consensus Standards
• References
–OSHA 29 CFR 1926 Subpart K Electrical
–NFPA 70E

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Dangers of Electricity
• Electric shock or electrocution
• Skin burns
• Falls
• Fire from electrical shorts or
as an ignition source
• Improper operation of power
equipment
About 5 workers are electrocuted every week in the United States
Burn caused by electricity

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Electricity – How it Works
• Electricity is the flow of energy
from one place to another
• Requires a source of power:
usually a generating station
• A flow of electrons (current)
travels through a conductor
• Travels in a closed circuit
Source
Load
Conductor
Switch

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Electrical Terms
• Current
– Flow of electric charge in a medium
• measured in Amperes (A)
• Voltage
– Measure of “push” available to motivate electrons
• measured in Volts (V)
• Resistance
– Measure of opposition to electric current
• measured in Ohms (Ώ)

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Electrical Terms
• Conductors
– Materials that allow electricity to flow
• Insulators
– Materials with high resistance to electricity
• Grounding
– A conductive connection to the earth which acts as
a protective measure

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Conductors / Insulators
Conductors
• silver
• copper
• gold
• aluminum
• iron
• steel
• brass
• bronze
• mercury
• graphite
• dirty water (salty water)
Insulators
• glass
• rubber
• oil
• asphalt
• fiberglass
• porcelain
• ceramic
• (dry) paper
• (dry) wood
• plastic
• air
• pure water

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Electrical Injuries
Two main types of electrical injuries:
• Direct
– Electrocution or death due to electric shock
– Electrical Shock
– Burns
• Indirect
– Falls

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Rules of Electricity
• Electricity travels in a complete/closed circuit
• Electricity always travels in the path of
least resistance
• Electricity always tries to travel to ground

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Electricity and People
• A person usually offers a
lesser resistance
for the electricity
• The person forms a
completed circuit when
touching the ground

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Discussion
• Will a bird resting on a high voltage, high
tension wire be electrocuted?

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Shock Severity
• You will get a shock if any part of the
body completes the electrical circuit
• Severity of the shock depends on:
– Path of current through the body
– Amount of current flowing
through the body (amps)
– Duration of the shocking current
through the body
• LOW VOLTAGE DOES NOT
MEAN LOW HAZARD!!

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Electrical Harm
1mA Barely perceptible
16mA Maximum current an average man
can grasp and “let go”
20-30mA Paralysis if respiratory muscles
100mA Ventricular fibrillation threshold
2Amps Cardiac standstill and internal
organ damage
*mA = milliampere = 1/1,000 of an ampere
*mA = milliampere = 1/1,000 of an ampere

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Burns
• Most common shock-related injury
• Occurs when you touch
electrical wiring or equipment
improperly used or maintained
• Typically occurs on hands
• Very serious injury that
needs immediate attention

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Falls
• Electric shock can also cause
indirect injuries like falls
• Workers in elevated locations
who experience a shock may
fall due to involuntary
movement of the muscles,
resulting in serious injury or
death

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General Electrical Hazards
• High-Voltage Overhead Power Lines
• Inadequate Wiring
• Damaged Cords and Wires
• Improper Grounding
• Overloaded Circuits
• Digging or Trenching Near
Underground Utilities
• Flammable materials

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Controlling Electrical Hazards
Electrical systems are engineered to be safe!
• Injuries / accidents typically occur when:
– Procedures are inappropriate
– Procedures are not followed or ignored
– Safety systems are circumvented
– Unsafe work practices
– Unsafe equipment / installation

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Inadequate Wiring
• Hazard
– Wire too small
– Distance too far
• Example: Portable tool with extension
cord wiring too small for the tool
– The tool draws more current than the cord
can handle, causing overheating &
possible fire without tripping breaker
– Breaker could be correct for circuit, but not
for smaller-wire extension cord
Wire gauge measures
wires ranging in size from
number 36 to 0 American
wire gauge (AWG)

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Use the Correct Wire
• Wire used depends on operation, building materials,
electrical load, and environmental factors
• Use fixed cords rather than flexible cords
• Use the correct extension cord (heavy duty)

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Defective Cords and Wires
• Worn / frayed cords must
be removed from service

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Damaged Cords
• Cords can be damaged by:
– Abrasion from adjacent materials
– Aging
– Door or window edges
– Staples or fastenings
– Sharp corners
– Hanging from nails
• Improper use can cause shocks,
burns or fire

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Cords and Wires
• Insulate live wires
• Inspect before use
• Use only 3-wire (grounded) type cords
• Use only cords marked for hard or extra-
hard usage
• Remove cords by pulling on the plugs
– not the cords

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Grounding
• Grounding creates
a low-resistance path
from a tool to the earth
to disperse unwanted current.
• When a short or lightning occurs,
energy flows to the ground,
protecting you from electrical
shock, injury and death.

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Improper Grounding
• Tools plugged into improperly grounded
circuits may become energized
• Removing the grounding pin from the plug

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Ground Tools & Equipment
• Ground power supply systems, electrical circuits,
and electrical equipment
• Frequently inspect electrical systems
to insure path to ground is continuous
• Inspect electrical equipment before use
• Don’t remove ground prongs from tools or
extension cords
• Ground exposed metal parts of equipment

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Use of GFCI
• Ground Fault Circuit Interrupter protects you
from shock
• GFCI’s are designed to sense an imbalance
in current flow over the normal path.
• If the current flow differs by more than
5mA, GFCI shuts off electricity in
1/40th of a second
• A GFCI is not an overcurrent device
like a fuse or circuit breaker.
• Test before each use.

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Power Tool Requirements
Hand held power tools must:
• Have three-wire cord with ground
plugged into a grounded receptacle,
OR
• Be double insulated
OR
• Be powered by a low-voltage
isolation transformer

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Overloaded Circuits
• Too many devices plugged into a circuit, causing
heated wires & possibly a fire
• Damaged tools overheating
• Lack of over-current protection
• Wire insulation melting, which may
cause arcing & fire where the
overload exists, even inside a wall

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Electrical Protective Devices
• GFCI, fuses, & circuit breakers
• Fuses & circuit breakers are
over-current devices.
• When there is too much current:
– Fuses melt
– Circuit breakers trip open
• Electrical system should be checked out by a qualified
electrician if circuit breakers or GFCI continue to trip

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Flammable Materials
• Flammable gases, vapors, liquids or
combustible dust can be ignited by static
electricity

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Proper Storage
Require specially designed electrical equipment
• Use “hazard location” or intrinsically safe equipment
• Use spark arrestors
• If stored in metal container, provide
proper bonding and grounding to
discharge static electricity

33. Safe Work Practices

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Electrical Cabinets
• Free from recognized hazards
• Labeling or certification required
• Check mechanical strength
and durability
• Electric equipment firmly
secured to the surface on
which it is mounted

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Electrical Equipment
• Barriers or guards to
prevent damage to
electrical equipment

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Panel Boards
• Electrical insulation
• Practical safeguarding
• Live parts by cabinets,
enclosures

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Cable Management
• Sufficient working space maintained around
equipment (3 to 4 feet required)

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Switches
• Disconnecting means identified

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Circuit Breakers
• Circuit breakers must clearly indicate open or
closed position
• Should identify what they control

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Isolation
Prevent unauthorized access with:
• warning signs
• secure location
• by location or elevation
– (7 feet / 2.1 meters)

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Extension Cords
• Must be used in continuous lengths with no splices

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Avoid Wet Conditions
• If you touch a live wire or other electrical component
while standing in water, you can get a shock
• Improperly grounded metal
switch plates & ceiling lights
are especially hazardous in
wet conditions
• Wet clothing, high humidity,
& perspiration increase your
chances of being electrocuted

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Industrial Plugs
• Provide a connection to the electrical mains rated at
higher voltages and currents than household plugs
and sockets.
• May have weatherproof covers, or may be interlocked
with a switch to prevent accidental disconnection of
an energized plug.
• Some types of connectors are approved for hazardous
areas where flammable gas may be present.
– such as coal mines or petrochemical plants

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Industrial Plugs

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Color Identification

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Distribution Panel, Wall Socket

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Clues that Hazards Exist
• Tripped circuit breakers or blown fuses
• Warm tools, wires, cords, connections, or
junction boxes
• GFCI that continually shuts off a circuit
• Worn or frayed insulation around wire or
connection

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Summary
• There are two main types of electrical injuries:
– Direct
• Electrocution or death due to electric shock
• Electrical Shock
• Burns
– Indirect
• Falls

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Summary
• Electrical Hazards in the Construction Site
– High-Voltage overhead power lines
– Inadequate wiring
– Damaged cords and wires
– Improper grounding
– Overloaded circuits
– Digging or trenching near underground utilities
– Flammable materials

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Summary
Methods of protection from electrical hazards
• Grounding
• Inspection
• Use of Signage
• Isolation
• Use of GFCI
• Use of overcurrent protective devices

51. Thank You