Electrical Safety
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Welcome to Electrical Safety!
• An average of one worker is electrocuted on the
job every day in the United States
• The purpose of this presentation is to give you
basic information to practice good electrical
safety in your labs and work spaces.
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Biological Effects of Electrical
Hazards (or, How Electricity
Can Hurt You)
The effects can vary depending on:
• Source characteristics (current,
frequency, and voltage).
• Duration of the contact.
• Current’s pathway through the body.
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Effects of Electrical Current in the
Human Body
Current
Effect
1 milliamperes (mA)
Faint tingle
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Effects of Electrical Current in the
Human Body
Current
Effect
1 milliamperes (mA)
Faint tingle
10-25 mA
Painful shock, loss of muscle control
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Effects of Electrical Current in the
Human Body
Current
Effect
1 milliamperes (mA)
Faint tingle
10-25 mA
Painful shock, loss of muscle control
50-150 mA
Extreme pain, respiratory arrest, severe
muscular contractions
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Effects of Electrical Current in the
Human Body
Current
Effect
1 milliamperes (mA)
Faint tingle
10-25 mA
Painful shock, loss of muscle control
50-150 mA
Extreme pain, respiratory arrest, severe
muscular contractions
1-4 amperes (A)
Heart stops; death likely
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Effects of Electrical Current in the
Human Body
Current
Effect
1 milliamperes (mA)
Faint tingle
10-25 mA
Painful shock, loss of muscle control
50-150 mA
Extreme pain, respiratory arrest, severe
muscular contractions
1-4 amperes (A)
Heart stops; death likely
5-12 A
Current drawn by typical household appliances
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Effects of Electrical Current in the
Human Body
Current
Effect
1 milliamperes (mA)
Faint tingle
10-25 mA
Painful shock, loss of muscle control
50-150 mA
Extreme pain, respiratory arrest, severe
muscular contractions
1-4 amperes (A)
Heart stops; death likely
5-12 A
Current drawn by typical household appliances
10 A
Cardiac arrest and severe burns; death
probable
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Effects of Electrical Current in the
Human Body
Current
Effect
1 milliamperes (mA)
Faint tingle
10-25 mA
Painful shock, loss of muscle control
50-150 mA
Extreme pain, respiratory arrest, severe
muscular contractions
1-4 amperes (A)
Heart stops; death likely
5-12 A
Current drawn by typical household appliances
10 A
Cardiac arrest and severe burns; death
probable
15 A
Lowest overcurrent at which a typical fuse or
circuit breaker operates
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Biological Effects of Electrical
Hazards (or, How Electricity
Can Hurt You)
The effects can vary depending on:
• Source characteristics (current,
frequency, and voltage).
• Duration of the contact.
• Current’s pathway through the body.
• Body impedance (resistance).
• Environmental conditions.
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Ohm’s Law
This is not
what kills you.
This is!
𝑉𝑜𝑙𝑡𝑎𝑔𝑒
𝐶𝑢𝑟𝑟𝑒𝑛𝑡 =
𝑅𝑒𝑠𝑖𝑠𝑡𝑎𝑛𝑐𝑒
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Types of Injuries
• There are four main types of electrical injuries:
Electrocution (death due to electrical shock)
Electrical shock
Burns
Falls
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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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What Should I Look For?
1. Improper use of extension cords
2. Damaged and poorly maintained electrical
equipment and wiring
3. Improperly grounded or insulated power tools
4. Overloaded circuits and inadequate wiring
5. No GFCI
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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, and can
be a trip hazard.
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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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Damaged and poorly maintained
equipment may create signifant
electrical hazards
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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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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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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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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 for protection of equipment
• When there is too much current:
 Fuses melt
Circuit breakers trip
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Ground-Fault Circuit Interrupter
(GFCI)
• 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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Types of GFCI
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Clues that Electrical Hazards Exist
• Tripped circuit breakers or blown fuses
• GFCI that shuts off a circuit
• Warm tools, wires, cords, connections, or junction boxes
• Worn or frayed insulation around wire or connection
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Summary
Hazards
• Exposed electrical parts
• Wires with bad insulation
• Damaged power tools and
equipment
• Ungrounded electrical
systems and tools
• Inadequate wiring
• Overloaded circuits
• Improper use of extension
cords
• All hazards are made worse
in wet conditions
Protective Measures
• Guard live parts
• Remove damaged
equipment from service
• Proper grounding
• Use GFCI’s
• Proper use of extension
cords
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