presentation for hazards and preventions of electrical

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