Transcript Electrical Safety

ELECTRICAL SAFETY!
It’s shocking!
OSHA 29 CFR
1910.332
Introduction
 An average of one worker is electrocuted on
the job every day.
 There are four main types of electrical
injuries:
 Electrocution (death due to electrical
shock)
 Electrical shock
 Burns
 Falls
Electrical Terminology
 Current – the movement of electrical charge
 Resistance – opposition to current flow
 Voltage – a measure of electrical force
 Conductors – substances, such as metals, that have
little resistance to electricity
 Insulators – substances, such as wood, rubber, glass,
and bakelite, that have high resistance to electricity
 Grounding – a conductive connection to the earth
which acts as a protective measure
Leading causes of injury
 Unsafe work practices
(cause of 75% of fatalities)
 Working with unsafe
equipment
 Working in an unsafe
environment
OSHA Definitions
Qualified worker vs. Unqualified Worker
Qualified
 One who is familiar with the construction and operation of the
equipment and hazards involved (licensed electrician).
Or
 One who is undergoing “on-the-job” training and has
demonstrated competency in performing the duties safely
(apprentice).
OSHA Definitions
 Qualified workers
 How to identify exposed energized parts
 How to safeguard or work on energized parts
 Unqualified workers
 How electricity works
 Risks of working with energized equipment
 Tasks to be performed only by qualified workers
Electrical Shock
• Received when current passes
through the body
• Severity of the shock depends on:
 Path of current through the body
 Amount of current flowing through
the body
 Length of time the body is in the
circuit
• LOW VOLTAGE DOES NOT MEAN
LOW HAZARD
Electrical Shock
Dangers of Electrical Shock
• Currents greater than 75 mA* can cause
ventricular fibrillation (rapid, ineffective
heartbeat)
• Will cause death in a few minutes unless
a defibrillator is used
• 75 mA is not much current – a small
power drill uses 30 times as much
Defibrillator in use
* mA = milliampere = 1/1,000 of an ampere
Electrical Shock
How is an electrical shock received?
• When two wires have different potential differences (voltages), current
will flow if they are connected together.
 In most household wiring, the black wires are at 110 volts relative to
ground.
 The white wires are at zero volts because they are connected to
ground.
• If you come into contact with an energized (live) black wire, and you are
also in contact with the white grounded wire, current will pass through
your body and YOU WILL RECEIVE A SHOCK.
Electrical Shock
• If you are in contact with an energized wire or any energized
electrical component, and also with any grounded object, YOU
WILL RECEIVE A SHOCK!!
• You can even receive a shock when you are not in contact with a
ground.
 If you contact both wires of a 240-volt cable, YOU WILL
RECEIVE A SHOCK and possibly be electrocuted.
Electrical Hazards
Shock
Blast
Arc
Rules of Electricity
 Electricity travels in a completed
circuit
 Electricity always travels in the path
of least resistance
 Electricity tries to travel to the
ground
Effects on the Human Body
 1 mA: Can be felt by the body
 2-10 mA: Minor shock, might result in a fall
 10-25 mA: Loss of muscle control, may not be

able to let go of the current
 25-75 mA: Painful, may lead to collapse or death
 75-300 mA: Last 1/4 second, immediately fatal
110/120 Volts = 60 mA
220/240 Volts = 120 mA
440/480 Volts = 240 mA
Severity Of Shock
Depends On:
 Amount of current flowing
through body
 The path it takes through the
body
 Elapsed time during shock
Body’s Resistance
Skin offers most of the body’s electrical resistance
 Increased resistance
 Thick and callused skin (foot or hand)
 Dry skin
 Decreased resistance
 Thin skin (inner forearm)
 Wet or sweaty skin
 Broken or abraded skin (scratches)
Conductor vs. Insulator
 Insulator
 Conductor
 Transfers electricity
 Stops electricity
 Does Not Conduct
electricity
General Electrical Hazards
 High-voltage overhead
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power lines
Damaged insulation on wires
Digging or trenching near
buried lines
Broken switches or plugs
Overloaded circuits
Overheated appliances or tools
Hazard Control
 Injuries typically occur when:
 Procedures are
inappropriate
 Procedures are not followed
 Safety systems are
circumvented
Portable Power Tools
 Inspect portable power tools
before every use!
 Never use damaged equipment.
 Tag it out of service
 Have it repaired or replaced
Portable Electric Equipment
 UL approved equipment and cords
 Graded for hazardous locations
 Extension cords must have a ground wire polarity plug.
 Inspect for frays, breaks or other damage to the cord insulation
 Inspect for grease, oil or chemicals on cords
 Do not unplug or raise equipment by cord
 Do not use around combustible atmospheres
(“Intrinsically Safe” only)
 Work in dry area - avoid water
Extension Cords
 Inspect and check for capacity
 For temporary work only
 Do not use as a rope
to pull or lift objects
 Should not be fastened with
staples or hung over hooks
Electrical Cord Inspection
 Deformed or mission pins
 Damaged outer jacket or
insulation
 Evidence of internal
damage
 If damaged, take out of
service until repaired
Grounding Equipment
 Most electrical equipment is
designed with a grounding system
 Do not use equipment with
damaged grounding connectors
 Do not use adapters that interrupt
the grounding connection
Static Electricity
 Created when materials rub together
 Can cause shocks or even minor skin burns
 Reduced or prevented by:
 Proper grounding
 Rubber matting
 Grounding wires, gloves, or shoes
Ground Fault Circuit Interrupters
 GFCIs reduce the likelihood of fatal shocks
 Detect small amount of earth current and automatically
switch off the power
 Used with extension cords and portable tools
 Fuses and circuit breakers protect equipment, not people
Most effective piece of safety
gear ever created…
Never touch anyone in
contact with electricity!
What to do in emergencies:
1. Shut off power
2. Call for emergency help
3. Administer First Aid/CPR
If unable to shut off power, use a wooden chair, pole, or PVC
to free the person.
Training
Train employees working with electric equipment in
safe work practices, including:
• Deenergizing electric equipment before
inspecting or making repairs
• Using electric tools that are in good repair
• Using good judgment when working near
energized lines
• Using appropriate protective equipment
Summary
Hazards
• Inadequate wiring
• Exposed electrical parts
• Wires with bad insulation
• Ungrounded electrical systems and
tools
• Overloaded circuits
• Damaged power tools and equipment
• Using the wrong PPE and tools
• Overhead power lines
• All hazards are made worse in wet
conditions
Protective Measures
• Proper grounding
• Using GFCI’s
• Using fuses and circuit
breakers
• Guarding live parts
• Proper use of flexible cords
• Training