Transcript Electrical Safety

CHEM 521 Safety Presentation
Hazard Symbols You Must Know
Take Electricity Seriously
• Over 30,000 non-fatal shocks occur each
year.
• Over 600 deaths occur annually due to
electrocution.
Source: Bureau of Labor Statistics
Electrical Accidents
• Leading Causes of Electrical Accidents:
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Drilling and cutting through cables
Using defective tools, cables and equipment
Failure to maintain clearance distance of 10 feet
Failure to de-energize circuits and follow Lockout/Tagout
procedures
Failure to guard live parts from accidental worker contact
Unqualified employees working with electricity
Improper installation/use of temporary electrical systems and
equipment
By-passing electrical protective devices
Not using GFCI (ground fault circuit interrupters) devices
Missing ground prongs on extension cords
Hazards of Electricity
• Shock – Most common and can cause electrocution or muscle
contraction leading to secondary injury which includes falls
• Fires – Enough heat or sparks can ignite combustible materials
• Explosions – Electrical spark can ignite vapors in the air
• Arc Flash - can cause burns ranging from 14,000 degrees f. to
35,000 degrees f
• Arc Blast – In a short circuit event copper can expand 67,000
times. The expansion causes a pressure wave. Air also expands
adding to the pressure wave
Fundamentals of Electricity
• Electrical current is the flow of electrons
through a conductor.
• A conductor is a material that allows
electrons to flow through it.
• An insulator resists the flow of electrons.
• Resistance opposes electron flow.
How Shocks Occur
• Current travels in closed circuits
through conductors (water, metal, the
human body).
• Shock occurs when the body becomes
a part of the circuit.
• Current enters at one point & leaves at
another.
Severity of the Shock
• Severity of the Shock depends on:
– Amount of current
• Determined by voltage and resistance to flow
– Path through the body
– Duration of flow through the body
– Other factors such as general health and
individual differences.
Effects of Current Flow
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More than 3 milliamps (ma): painful shock
More than 10 ma: muscle contraction
More than 20 ma: considered severe shock
More than 30 ma: lung paralysis - usually temporary
More than 50 ma: possible ventricular fibrillation
(usually fatal)
• 100 ma to 4 amps: certain ventricular fibrillation (fatal)
• Over 4 amps: heart paralysis; severe burns
Electrical Isolation
• We can be safe by keeping electricity away
from us. We can:
– Insulate the conductors.
• Example: The insulation on extension cords.
– Elevate the conductors.
• Example: Overhead powerlines.
– Guard the conductors by enclosing them.
• Example: Receptacle covers, boxes, & conduit.
Insulating the Conductors
• The first way to safeguard workers from
electrically energized wires is through
insulation.
• Rubber and plastic is put on wires to
prevent shock, fires, short circuits and for
strain relief.
• It is always necessary to check the
insulation on equipment and cords before
plugging them in.
• Remember, even the smallest defect will
allow leakage!
Defective Extension Cords
Photos depict hazardous condition
Defective Cord Incident
• Worker attempted to climb
scaffold with electric drill.
• Drill’s cord was damaged
with bare wires showing.
• The bare wire contacted the
scaffolding.
• The worker died!
Depicts hazardous condition
Guarding the Conductors
• The third way to safeguard workers from
electrically energized wires is by guarding
them.
• Covers, boxes, and enclosures are often put
around conductors to prevent worker contact.
• It is always necessary to check that electrical
boxes and panels are covered and free from
missing “knock-outs”.
• Remember, electric equipment operating at 50
volts or more must be guarded!
Photo depicts hazardous condition
Guarding the Conductors
Photos depict hazardous condition
Guarding the Conductors
Photos depict hazardous condition
Equipment Grounding
• We can be safe by providing a separate, low
resistance pathway for electricity when it
does not follow normal flow (ground prong).
• Grounding gives the stray current somewhere
to go and keeps you from becoming part of
the circuit.
Can You Rely on Grounding?
• Grounding will not work if the electricity can
flow through you more easily than the
ground. This can happen when:
– Your tool doesn’t have a ground pin.
– You’re working in wet locations.
– You’re touching a metal object.
What Must be Grounded?
• All circuits and extension
cords.
• All noncurrent carrying metal
parts.
• Portable & semi-portable
tools and equipment unless
double insulated.
Do Not Eliminate the Ground!
You become the next-best path for current!
Photos depict hazardous condition
Do Not Reverse Polarity
The prongs are different
sized so you can’t turn
the plug around. If you
do, the electrical fields
within the motor are always
energized. If there is
moisture present, the case
is likely to be “hot”. Even
with double-insulated tools,
you still could get a shock.
Photo depicts hazardous condition
Circuit Interruption
• We can be safer by automatically shutting off the
flow of electricity in the event of leakage,
overload, or short circuit.
• Ground Fault Circuit Interrupters (GFCI) are
circuit protection (or “overcurrent”) devices that
protect you, the worker.
• Circuit breakers & fuses protect equipment, not
you, because they take too much current & too
much time to trip.
Checking for Ground Continuity
What else we should we notice here?
Photo depicts hazardous condition
Temporary Wiring
• There must be separate circuits for electric
tools and lighting, each labeled as such.
• Light circuits do not require a GFCI.
– Unless used in a wet location.
• Test branch circuits before use.
• Maintain vertical clearances.
• Insulate wires from their supports.
SUBPART
Extension Cords and Cables
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Must be in good shape without splices.
Cannot be secured with staples, nails or bare wire.
Must be protected from damage.
Must have a ground pin.
Should be inspected regularly and pulled from
service if defective.
• Cannot be repaired with electrical or duct tape.
Must repair with heat-shrink sleeve or
bonding/vulcanizing tape to retain original
insulation properties.
Photos depict hazardous condition
Photo depicts hazardous condition
Safe Work Practices
• De-energized circuits and equipment must
be locked/tagged out.
SUBPART
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Safe Work Practices
• No metal ladders for or near electrical
work.
• No wet hands when plugging or
unplugging cords/equipment.
• No raising or lowering tools by the
cord.
• Unless equipment is designed for it,
cannot be used in damp and wet
locations.
Photo depicts hazardous condition
SUBPART
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Summary – Hazards & Protections
Hazards
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Protective Measures
Inadequate wiring
 Proper grounding
Exposed electrical parts
 Use GFCI’s
Wires with bad insulation
Ungrounded electrical systems and  Use fuses and circuit breakers
tools
 Guard live parts
Overloaded circuits
 Lockout/Tagout
Damaged power tools and
 Proper use of flexible cords
equipment
Using the wrong PPE and tools
 Close electrical panels by
Competent Person
Overhead power lines
All hazards are made worse in wet  Employee training
conditions
 Ensure Competent Person on
Damaged extension cords
site
Unqualified workers doing electrical  Use proper approved electrical
work
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equipment
Qualified person install
electrical devices
Report any concerns
• If you have any safety concerns about the lab you
are working in or the people working around you,
you can contact:
– Your lab instructor
– Dr. Neal Tonks – Head of the departmental safety
committee
– Dr. Pamela Riggs-Gelasco – Department Chair for
Chemistry and Biochemistry
– Dr. Jim Deavor, Associate Dean of the School of
Science and Mathematics.