Transcript Document

Technical Services (HQ)
Safety Department
Welcome!
The reason for this Program
 Electricity is the most commonly used at
construction sites.
 Unsafe use of Electricity can cause serious
accidents including electrocution (death).
The goal of this Program
 Learn basic fundamentals of electricity.
 Learn how electricity effects human body.
 Learn to identify common electrical hazards and
protection devices.
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Welcome!
 The program is not designed to
teach you to work on Electrical
Equipment.
 If you find any problem with
electrical equipment, you should
report it to supervisor/engineer.
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Basic Fundamentals of Electricity
Electricity flows through conductors – metals,
water, the human body etc.
Insulators are non-conductors – Rubber, wood
etc.
The Human Body is a Conductor.
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Basic Fundamentals of Electricity
Voltage.
Electric Pressure (water pressure).
Current
Electricity Flow Rate in amperes (water flow rate).
Impedance/Resistance.
Resistance to flow of current/electricity (pipe friction)
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Basic Fundamentals of Electricity
Circuit.
Path of flow of current/electricity.
Circuit Elements
Objects which are part of a circuit and through which
current flows.
Fault.
Current flow through an intended path.
Grounding.
Ground conductor provides connection between
equipment and earth.
Provides protection from electric shock.
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Basic Fundamentals of Electricity
Basic Rules
Circuit is not live until current flows.
Electrical current won’t flow until circuit is complete
(power source to equipment (load) to power source).
Current prefers to flows through the least resistance
path.
Current in a circuit = Voltage/Impedance (Resistance).
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How you get an electric shock?
Electricity travels in closed circuit. You get
shock when the body becomes part of
electrical circuit – current enters the body at
one point and leaves at another point.
Shock occurs when a person contacts:
Both wires of an energized circuit.
One wire of an energized circuit and ground.
A metallic part in contact with an energized circuit
while the person is in contact with ground.
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How electrical current affects
human body
Three factors that affect the severity of the
Shock.
Amount of current that flows through the body.
Path of the current through the body.
Length of time the body is in circuit.
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How electrical current affects
human body
Other factors that may affect the severity of the
shock
The voltage of the circuit.
The presence of moisture in the
environment/body.
The general health of the person (body
resistance).
The phase of the heart cycle when the shock
occurs.
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Probable effect of shock on
human body
General relationship for a 50 cycles, hand-to-foot
shock of one second duration.
1mA
Slight tingling sensation.
5 mA
Slight shock; not painful but disturbing. Average
individual can let go.
6-30 mA
Painful shock, muscular control is lost. This is
called freezing current.
50-150
mA
Extreme painful, respiratory arrest, severe
muscular contractions. Death is possible.
10004300 mA
Ventricular fibrillation (the rhythmic pumping
action of the heart ceases.) Muscular contraction
and nerve damage occur. Death is most likely.
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Probable effect of shock on
human body
Under dry conditions, human skin is very
resistant. Human body resistance is
approximately 100 kilo ohms
Dry condition current = 230/100,000 = 2.3
mA
Under wet conditions, wet skin dramatically
drops the body’s resistance to approximately
1 kilo ohm.
Wet condition current = 230/1000 = 230 mA
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Probable effect of shock on
human body
Human Resistance to Electrical Current
Body Area
Resistance (ohms)
Dry Skin
100,000 to 600,000 ohms
Wet Skin
1,000 0hms
Internal body – hand to
foot
400 to 600 ohms
Ear to ear
(about) 100 ohms
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Probable effect of shock on
human body
If the extensor muscles are excited by the
shock, the person may be thrown away. This
often result in a fall from elevation that may
kill the victim.
If muscular contraction caused by stimulation
does not allow the victim to free himself from
electric circuit, even low voltage could be
dangerous, because degree of injury increases
with time the body is in contact with circuit.
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Probable effect of shock on
human body
Low Voltage does not imply low Hazard.
100 mA for 3 seconds = 900 mA for 0.03
seconds in causing fibrillation.
A difference of less than 100 mA exists
between a current that is barely perceptible
and one that can kill.
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Probable effect of shock on
human body
High Voltage greatly reduces the body’s
resistance by breaking down human skin. Once
the skin is punctured, the lowered resistance
results in heavy current through the human
body.
At 1000 volts, Current = 1000/500 = 2 Amps.
This can cause cardiac arrest and serious
damage to internal organs.
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Injuries to human body from
electric shocks
Shock related injuries include:
Electric Burns.
Internal Injuries.
Involuntary muscle contractions.
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Injuries to human body from
electric shocks
Electric Burns.
Electric burns are the result of heat generated by the
flow of electric current through the body and cause
tissue damage.
High temperature produced by electric arc or explosion
cause flash burns.
Thermal contact burns occur when skin comes in
contact with overheated electric equipment.
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Injuries to human body from
electric shocks
Internal Injuries.
Excessive current flowing through the human
body cause serious damage to internal organs
including internal bleeding, tissue damage,
nerve or muscle damage. These internal
injuries may not be immediately apparent to
victim or others, however if left untreated,
these can result in death.
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Injuries to human body from
electric shocks
Involuntary Muscle Contraction.
Normal muscle contraction is caused by very small
amount of current that is created inside our body.
Muscles violently contract when stimulated by excessive
current. These can cause damage to 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 prolong contact with current. This may lead
to injury or death or victim to fall from elevation.
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Injuries to human body from
electric shocks
Severity of Electric Shocks
Injuries from electric shock are less severe
when the current does not pass through or near
nerve centers and vital organs. However in
majority of accidents at construction sites the
current flows through hand to feet. Since such a
path involves both heart and lungs, the shocks
are usually serious.
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What are the hazards in use of
electricity ?
Contact with Live Parts.
Lack of ground fault protection.
Path to ground missing or discontinuous.
Equipment not used properly
Improper use of extension and flexible
wires/cords.
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What are the hazards in use of
electricity ?
Contact with live parts.
Temporary wiring that caries high voltage (over 440
volts) is guarded and fenced to keep out unauthorized
personnel.
Area around electrical equipment is not used as
passageways when energized parts are exposed.
There is adequate illumination and those working on the
equipment are not endangered by live parts. Theses
workers are provided with rubber gloves.
Electrical boards or live parts are protected by suitable
enclosures and appropriate warning signs displayed.
Electrical equipment and wiring are in safe condition.
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What are the hazards in use of
electricity ?
Lack of ground fault protection
Due to the nature of work at construction site,
electrical equipment are prone to excessive
wear and tear that results in insulation breaks,
short circuits and exposed wires. If there is no
ground fault protection, it can cause current
through worker’s body resulting in electric
shock.
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What are the hazards in use of
electricity ?
Lack of ground fault protection
Use earth leakage circuit breakers for all 230 volt, single
phase, 15 amps hand held electric tools.
Provide earth to all 3 phase electric equipment through
assured equipment grounding conductor program.
Follow manufacturers’ recommended testing instructions to
ensure GFCI is working properly.
Use tools and equipment according to the manufacturer's
instructions.
Visually inspect all equipment for fray cords, missing ground
links, cracked tool casing etc.
Ground conductor is not used as the return path.
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What are the hazards in use of
electricity ?
GFCI (Ground-fault circuit interrupter)
A device that detects an insulation failure by comparing
the amount of current flowing to electrical equipment with
the amount of current returning from the equipment.
Whenever the difference is greater than 5 milliamps, the
GFCI trips and thereby interrupts the flow of electricity.
It is also called ELCB (Earth Leakage Circuit Breaker)
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What are the hazards in use of
electricity ?
Path to ground missing or discontinuous.
If the power supply to electrical equipment at
site is not grounded or the path is broken, fault
current may travel through worker’s body
causing accident (electric shocks etc)
Ground all power supply systems, distributions boards,
electrical equipment.
Inspect electrical systems frequently to ensure that the
path to ground is continuous.
Visually inspect all electrical equipment before use.
Remove any defective equipment from service.
Use double insulated tools.
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What are the hazards in use of
electricity ?
Equipment not used properly
If electrical equipment is used in a manner for
which it is not designed, safety feature built in by
the manufacture may not work and may damage
the equipment or cause injury.
Using circuit breakers or fuses with wrong rating for over
current protection e.g. using 20 amp circuit breaker for
15 amp tool.
Using tools or cords with worn insulation or exposed
wires.
Using only two wires for three wired tools.
Using multi-receptacle boxes and placing them on
ground.
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What are the hazards in use of
electricity ?
Improper use of extension and flexible
wires/cords.
The normal wear and tear on extension/flexible
wires can loosen or expose wires and may
create hazardous conditions.
Remove cords from receptacles by pulling on the plug,
not wire.
Use extension cords that are 3-wired type and are for
hard usage.
Flexible cords are not subjected to mechanical injury.
Use flexible cords in continuous length without splices.
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What are the hazards in use of
electricity ?
Flexible cords are not placed near/in water/liquids.
Flexible cords are equipped with metal clad industrial
plugs.
Flexible cords are used for only portable tools.
Inspect cords regularly and remove any defective cords.
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What to do – in case of electrical
accidents
Electrical accidents are very serious. Knowing
what to do can make a life-or-death difference.
Respond immediately in case of electrical
emergencies. There are:
Electrical Fires.
Electrical Shocks.
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What to do – in case of electrical
accidents
Electrical Fires – Electrical fires are different
from other fires, because water conducts
electricity, throwing water may cause the fire to
become bigger. Take these steps.
Switch off the main power supply.
Never use water on electrical fires.
Use only dry chemical powder or carbondioxide type fire extinguisher.
Call local fire brigade and inform that it is
electrical fire.
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What to do – in case of electrical
accidents
Electric Shock – If some one has got an electric
shock, it may be possible that he is still in
contact with source of electricity. Do NOT touch
the person or anything he is touching. You could
also become part of electric circuit and get a
shock. Take these steps:
 Switch off the main power supply.
 Call for help.
 When the victim is not in contact with
electricity you may give first aid. This may
include CPR.
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What if some one is injured
 Since the most common result of electrical
accident is failure of the nervous which
controls breathing, it is important the the
victim be applied to cardiopulmonary
resuscitation (CPR).
 The technique should be continued until
victim is revived or death is diagnosed by a
physician.
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What if some one is injured
What is Cardiopulmonary resuscitation (CPR)
• Cardiopulmonary resuscitation is a lifesaving technique
useful in many emergencies including cardiac arrest due
to electric shocks.
• Cardiac arrest is often caused by an abnormal heart
rhythm called ventricular fibrillation (VF). When VF
develops, the heart quivers and doesn't pump blood. The
victim in VF cardiac arrest needs CPR and delivery of a
shock to the heart, called defibrillation. Defibrillation
eliminates the abnormal VF heart rhythm and allows the
normal rhythm to resume.
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What if some one is injured
 CPR involves a combination of mouth-to-mouth rescue
breathing and chest compression that keeps
oxygenated blood flowing to the brain and other vital
organs until more definitive treatment can restore a
normal heart rhythm.
 When the heart stops, the absence of oxygenated blood
can cause irreparable brain damage in only a few
minutes. Death will occur within 8 to 10 minutes.
St. John Ambulance Society provides
necessary training on CPR
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What if some one is injured
Possibility of revival of electric shock victim
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Thank you
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