Transcript NEWESD Electrical

Basic Electrical Safety
WAC 296-800-280
Concerned About Electricity?
• How many sets of holiday
lights do you plug into one
extension cord?
• Do you still use your hot
and sparking electric drill?
• Is your vacuum cleaner’s
cord twisted and frayed?
• Have you installed outlet
covers to protect small children’s
probing fingers?
Rules of Electricity
 Electricity travels in a completed circuit
 Electricity always travels in the path of
least resistance
 Electricity tries to travel to ground
 Shock occurs when body becomes part of
the electrical circuit
How Electricity Works
Substances with very little resistance to the flow of electrical current
are called conductors. Examples are metals.
Substances with such a high resistance that they can be used to
prevent the flow of electrical current are called insulators. Examples
are glass, porcelain, rubber, plastic, and dry wood..
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)
Additional Resistance
• Gloves
• Shoes
• Insulating Mats
Grounding
The term "ground" refers to a conductive body, usually the earth.
"Grounding" a tool or electrical system means intentionally creating a lowresistance path to the earth. When properly done, current from a short from
follows this path, thus preventing the buildup of voltages that would
otherwise result in electrical shock, injury and even death.
Improper
grounding
Inadequate Grounding
(Path Of Ground Missing Or Discontinuous)
Am I In Danger?
If the power supply to the electrical equipment
at your site is not grounded or the path has
been broken, fault current may travel through a
worker's body, causing electrical burns or death
Even when the power system is properly
grounded, electrical equipment can instantly
change from safe to hazardous because of
extreme conditions and rough treatment.
Removing the ground pin from a plug
to fit an ungrounded outlet not only
means your work area is unsafe, but
makes the cord unfit for future work
where there is grounding.
Death due to inadequate grounding
Ground Wire Not Attached
A fan connected to a 120-volt electrical system via an extension cord provided
ventilation for a worker performing a chipping operation from an aluminum stepladder.
The insulation on the extension cord was cut through and exposed bare, energized
conductors which made contact with the ladder. The ground wire was not attached on
the male end of the cord's plug. When the energized conductor made contact with the
ladder, the path to ground included the worker's body, resulting in death.
Electrical Shock Internal Injuries
Excessive electricity flowing through the human body can
cause serious damage to internal organs.
Resulting medical problems include hemorrhage (or internal
bleeding), tissue destruction, and nerve or muscle damage.
These internal injuries may not be immediately apparent to the
victim or observers; however, left untreated, they can result in
death.
Involuntary Muscle Contraction
Normal muscle contraction is caused by very small amounts of electricity that
are created within our bodies. Muscles violently contract when stimulated by
excessive amounts of electricity.
These involuntary contractions can damage muscles, tendons, and ligaments,
and may even cause broken bones. If the victim is holding an electrocuting
object, hand muscles may contract, making it impossible to drop the object
and prolonging contact with the current.
Also, injury or death may result when violent muscle contractions cause
workers to fall from ladders and scaffolds or inadvertently strike other objects.
Contact with Power Lines
Overhead power lines are
un-insulated and can carry
tens of thousands of volts,
making them extremely
dangerous to employees
who work in their vicinity.
Stay at least 10 feet
Away from power lines
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Overhead and buried power lines at a
construction site are especially hazardous
because they carry extremely high voltage. Fatal
electrocution is the main risk, but burns and falls
from elevation are also hazards. Using tools and
equipment that can contact power lines increases
the risk.
Examples of equipment that can contact power
lines:
Backhoes
Concrete pumpers
Cranes
Long-handled cement finishing floats
Metal building materials
Metal ladders
Raised dump truck beds
Scaffolds
Hazard Control
• Injuries typically occur
when:
– Procedures are
inappropriate
– Procedures are not
followed or ignored
– Safety systems are
circumvent
Power Tools
 Avoid accidental starting. Do not hold fingers on the switch button while
carrying a plugged-in tool.
 Use gloves and appropriate safety footwear when using electric tools.
 Store electric tools in a dry place when not in use.
 Do not use electric tools in damp or wet locations unless they are
approved for that purpose.
 Ensure that cords from electric tools do not present a tripping hazard.
 Remove all damaged portable electric tools from use and tag them:
"Do Not Use."
 Use double-insulated tools.
Power Tools
Hand-held tools manufactured with non-metallic cases are called
double-insulated. If approved, they do not require grounding under
the National Electrical Code. Although this design method reduces
the risk of grounding deficiencies, a shock hazard can still exist.
Double insulated
marking
Portable Power Tools
• Inspect portable power tools
• Never use damaged equipment
– Tag it out of service
– Have it repaired or replaced
• Never use portable power equipment in
wet or damp areas
• Stop using power tools if they become hot
or start sparking
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
metal hooks or nails
Electrical Cord Inspection
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Deformed or missing pins
Damaged outer jacket or insulation
Evidence of internal damage
If damaged, take out of service until
repaired
OSHA prohibits using tape to repair
electrical cords
Circuit Protection
• Energize or de-energize with appropriate
switches, breakers, etc.
• Do not energize or de-energize with fuses,
terminal lugs, or cable splice connections
• If circuit protection device is tripped—
inspect (this may be you last warning)
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
• NEVER cut the ground leg (third prong) off
of a plug. It is there to protect you!
Examples of Prohibited Uses of
Flexible Cords
Substitute for
fixed wiring
Run through walls,
ceilings, floors,
doors, or windows
Concealed behind
or attached to
building surfaces
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
Summary
• Electricity will try to reach ground even if it
means going through a person
• Even the “small” voltage from your home
can cause serious injury
• Always inspect power tools and cords and
do not use them if damaged
• Do not attempt to repair electrical
equipment unless trained and qualified
water + electricity = danger
Strained
Power cord
Replace missing
outlet covers
Tripping hazard
More Information
NIOSH – Electrical Safety – Safety & Health Training for Electric Trades
OSHA Construction eTool – Electrical Incidents
DOSH Construction Standard – Electrical Rules
eLCOSH – Basic Electrical Safety
eLCOSH – Electrocution
eLCOSH – Why GFCIs Fail
eLCOSH – Protection from Electric Shock and Arc Flash
OSHA Fact Sheet – Working Safely with Electricity