Technical Services (HQ)

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Electrical
Safety
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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 wont 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.
1000-4300 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 bodys 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 bodys
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 workers
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 workers 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 carbon-dioxide
  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. Defibrillatio
  n 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