Download Electrical Safety Introduction - Environmental Health and Safety

Electrical Safety - Laboratory Safety Seminar
09/27/2011
Electrical Safety
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Introduction
• There are four main types of electrical injuries:
Electrocution (death due to electrical shock)
Electrical shock
Burns
Falls
Around 300 workers were electrocuted in 2008
and 220 in 2009.
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Electrical Safety - Laboratory Safety Seminar
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Electrocution (Image very
graphic)
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Biological Effects of Electrical
Hazards
The effects can vary depending on
-Source characteristics (current,
frequency, and voltage).
- Body impedance and the current’s
pathway through the body.
- How environmental conditions affect
the body’s contact resistance.
- Duration of the contact.
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Electrical Safety - Laboratory Safety Seminar
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Electrical Safety - Laboratory Safety Seminar
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Electrical Burns
• Most common shock-related,
nonfatal injury
• Occurs when you touch
electrical wiring or equipment
that is improperly used or
maintained
• Typically occurs on the hands
• Very serious injury that needs
immediate attention
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Falls
• Electric shock can also cause
indirect or secondary injuries
• Workers in elevated locations
who experience a shock can
fall, resulting in serious injury
or death
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Recognizing Hazards
1. Exposed electrical parts
2. Wires with bad insulation
3. Electrical systems and tools that are not
grounded or double –insulated
4. Damaged power tools and equipment
5. Inadequate wiring
6. Overload circuits
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Guarding of Live Parts
• Must guard live parts of electric
equipment operating at 50 volts or
more against accidental contact by:
 Approved cabinets/enclosures, or
 Location or permanent partitions
making them accessible only to
qualified persons, or
 Elevation of 8 ft. or more above
the floor or working surface
• Mark entrances to guarded
locations with conspicuous warning
signs
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Cabinets, Boxes, and Fittings
• Junction boxes, pull boxes
and fittings must have
approved covers
• Unused openings in cabinets,
boxes and fittings must be
closed (no missing knockouts)
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Hand-held sander has exposed
wires
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Grounding and Double
Insulation
• Hand-held electric tools pose a
potential danger because they make
continuous good contact with the hand
• To protect you from shock, burns, and
electrocution, tools must:
 Have a three-wire cord with ground
and be plugged into a grounded
receptacle, or
 Be double insulated
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Equipment without a
grounding conductor
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Equipment with a grounding
conductor
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Electrical Safety - Laboratory Safety Seminar
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Grounding Path
• The path to ground from
circuits, equipment, and
enclosures must be
permanent and continuous
• Violation shown here is an
extension cord with a
missing grounding prong
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Ground-Fault Circuit Interrupter
• This device protects you from dangerous
shock
• The GFCI detects a difference in current
between the black and white circuit wires
(This could happen when electrical
equipment is not working correctly,
causing current “leakage” – known as a
ground fault.)
• If a ground fault is detected, the GFCI
can shut off electricity flow in as little as
1/40 of a second, protecting you from a
dangerous shock
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How GFCI works
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GFCI
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Inadequate Wiring Hazards
• A hazard exists when a conductor is
too small to safely carry the current
• Example: using a portable tool with
an extension cord that has a wire too
small for the tool
 The tool will draw more current
than the cord can handle, causing
overheating and a possible fire
without tripping the circuit breaker
 The circuit breaker could be the
right size for the circuit but not for
the smaller-wire extension cord
Wire Gauge
WIRE
Wire gauge measures
wires ranging in size from
number 36 to 0 American
wire gauge (AWG)
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Control Inadequate Wiring
Hazards
The wire must be able to handle the
current. Its insulation must be appropriate
for the voltage and tough enough for the
environment.
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Electrical Safety - Laboratory Safety Seminar
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Overload Hazards
• If too many devices are
plugged into a circuit, the
current will heat the wires to
a very high temperature,
which may cause a fire
• If the wire insulation melts,
arcing may occur and cause
a fire in the area where the
overload exists, even inside
a wall
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Electrical Protective Devices
• Fuses and circuit breakers are overcurrent
devices
When there is too much current:
Fuses melt
Circuit breakers trip open
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Clues that Electrical Hazards Exist
•
•
•
•
Tripped circuit breakers or blown fuses
Warm tools, wires, cords, connections, or junction boxes
GFCI that shuts off a circuit
Worn or frayed insulation around wire or connection
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Use of Flexible Cords
• More vulnerable than fixed wiring
• Do not use if one of the recognized
wiring methods can be used instead
• Flexible cords can be damaged by:
 Aging
 Door or window edges
 Staples or fastenings
 Abrasion from adjacent materials
 Activities in the area
• Improper use of flexible cords can
cause shocks, burns or fire
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Permissible Uses of Flexible Cords
Examples
Pendant, or
Fixture Wiring
Portable lamps,
tools or appliances
Stationary equipmentto facilitate interchange
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Prohibited Uses of Flexible Cords
Examples
Substitute for
fixed wiring
Run through walls,
ceilings, floors,
doors, or windows
Concealed behind
or attached to
building surfaces
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Energized Work
•
•
•
EXEMPTION 1
De-energizing introduces additional or increased hazards. Examples include
interruption of life support equipment, deactivation of emergency alarm
systems, shutdown of hazardous location ventilation equipment, or removal
of illumination for an area.
EXEMPTION 2
De-energizing is infeasible due to equipment design or operational
limitations. Examples include testing of electrical circuits that can only be
performed with the circuit energized, and work on circuits that form an
integral part of a continuous industrial process in a chemical plant that
would otherwise need to be completely shutdown in order to permit work on
one circuit or piece of equipment.
EXEMPTION 3
Live parts that operate at less than 50V to ground need not be de-energized
if there will be no increased exposure to electrical burns or to explosion due
to electric arcs. Explain specifics for this work:
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Electric Arc
35,000 °F
Molten Metal
Pressure Waves
Sound Waves
Copper
Vapor:
Solid to Vapor
Expands by
67,000 times
Shrapnel
Hot Air-Rapid Expansion
Intense Light
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Lockout/Tagout
(when servicing equipment)
(1) Shut down the machine or equipment
(2) Completely isolate the machine using the
appropriate energy-isolating devices
(3) Make sure a lockout or tagouot device is
applied for each energy-isolating device
and only by the authorized employee doing
the service or maintenance
(4) Make sure all potentially hazardous stored
or residual energy is relieved, disconnected
or restrained
(5) Notify affected employees
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Summary
Hazards
• Exposed electrical parts
• Wires with bad insulation
• Ungrounded electrical
systems and tools
• Damaged power tools and
equipment
• Inadequate wiring
• Overloaded circuits
• All hazards are made worse
in wet conditions
Protective Measures
• Guarding live parts
• Proper grounding
• Using GFCI’s
• Using fuses and circuit
breakers
• Proper use of flexible
cords
• Proper use of PPE
• Training
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