Download Electrical Safety Onboard

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INTRODUCTION
• Three Important Commodities – Air ,
Water and Electricity
• Electricity – Clean and Efficient form of
Energy
• Respect Electricity it respects you
• Direct Working – Engineers, Technicians
and Professionals
• Indirect Working – Every Individual
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Electricity?
• Form of Energy – i.e. power to do or move
things
• Generated in power plants
• Brought to users ( termed loads) through
transmission lines – distribution lines
• When a device is plugged in circuit is completed
• Electricity travels through conductors – Al / Cu
• Human body – a good conductor – mostly water
• Electricity propagates at SPEED of Light 300
m/us
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Electricity ? (Contd…)
• Insulators – Confine Electricity – Glass –
Plastic – Ceramic – Rubber
• If Insulation - damaged or broken –
Electricity – leaks causes shock
• If an outlet – overloaded – Insulation
overheats and melts
=>
Fire or Shock
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How Does Electricity Hurt?
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Attempts to flow to ground
Takes short cuts
Good conductors give easy path
Water & metals are good conductors
Human body containing mostly water is a great
conductor
• If human body in the path – seriously hurt or
killed
• Desirable to keep appliances away from electric
circuits
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Electricity Hazards
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Shock – when human body in the path
Direct effect – Injury or death ~ 30 mA causes
death
• Indirect effects – result in falls or movement
leading to injury or death
• Basic ways Shock arises:
1. When in contact with both wires
2. When in contact with a wire and ground
3. When in contact with a metal part in contact
with a wire in a circuit and ground
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Electricity Hazards (Contd…)
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Burns :
When in contact with electrical circuit
Improperly used or maintained equipment
Typically on the hands ( arms)
Arc Blast:
Arise from high current arcs through air
Initiated by contact between energized parts
Accidentally by persons working on energized parts
Equipment failure due to fatigue or abuse
Temperatures reach 35,0000 F
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Arc Blast Hazards
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Thermal Radiation :
degree of injury depends on Skin Color, area of
contact and type of clothing
Minimized by Proper Clothing, maintaining working
distances and over-current protection
Pressure Wave Generation:
High Energy Arcing Faults lead to High Pressure
Typically 2’ away from 25 kA pressure experienced
480 pounds
Leads to serious ear damage – memory loss – due to
mild concussions
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Arc Blast Hazards (Contd…)
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Projectiles :
Pressure waves propel large objects over considerable
distances
Enough to melt copper and aluminum components
Burns more intense than injury from projectiles
Explosions:
occur due to ignition of explosive mixtures in the
atmosphere ( or environment)
Flammable vapors generated by source and process
Ignition due to overheated conductors or equipment or
normal arcing at switch contacts
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M.Sudhakaran
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Electrical Fires
• Electricity is most common cause of Fire – both
at home and in office
• Main cause is use of defective electrical
equipment and misuse of electrical apparatus
• High resistance connections being primary
source of ignition
• High resistance connections occur either due to
improper splicing of wires or improper
connection of receptacles/ switches specially
when employing aluminum conductors
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Effect of Shock on Human Body
• Factors responsible :
1. Current
2. Voltage
3. Resistance
4. Path Through the body
5. duration of Shock and
6. Muscular Structure
Less Musculature lower threshold current
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Electric
Current
(1
second
contact)
Physiological Effect
1 mA
Threshold of feeling, tingling sensation.
5 mA
Accepted as maximum harmless current
10-20
mA
Beginning of sustained muscular contraction ("Can't let go"
current.)
100-300
mA
Ventricular fibrillation, fatal if continued. Respiratory function
continues.
6A
Sustained ventricular contraction followed by normal heart rhythm.
(Defibrillation). Temporary respiratory paralysis and possibly
burns.
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Electric Current
(1 second contact)
Voltage required to produce
the current with assumed
body resistance:
100,000 ohms
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1,000 ohms
1 mA
100 V
1V
5 mA
500 V
5V
10-20 mA
1000 V
10 V
100-300 mA
10000 V
100 V
6A
600000 V
6000 V
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Shock Parameters
• Current & voltage
1. Though at High Voltages – massive
destruction at the point of contact
2. Current causes detrimental effect of Electric
shock,
3. Though I = v/r holds good, contact resistance
varies depending on local conditions
4. All domestic appliances can give fatal currents
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Effect of Currents
• Currents > 10 mA cause painful shock
• 100 – 200 mA can be lethal
• As ac current increases tingling sensation
finally leading to contraction of the
muscles
• Accompanied by heat sensation
• Develops pain and voluntary control is lost
• Around 15 mA victim can not let go termed
“Let – go threshold”
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Effect of Currents Contd…
• Around 100 mA – ventricular fibrillation
occurs i.e. very rapid uncoordinated
contractions of the ventricles of the heart
with loss of synchronization between heart
beat and pulse beat
• Finally leads to death
• (Ventricular fibrillation (VF) is a severely
abnormal heart rhythm (arrhythmia) that
can be life-threatening).
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Resistance
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Varies with
Moisture Content
Pressure at the Contact Point
Area of Contact
Epidermis presents very high resistance under dry
conditions, becomes lower when wet, or due to cuts or
break in skin
Shock severity higher
With increase in contact pressure
With increase in contact area
Resistance decreases with voltage
Due to Broken skin at higher voltages
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Current Paths
• Path Affects the degree of injury
• Small current from one extremity, through
heart, to the other extremity causes severe
injury or electrocution
• When current flows through a portion of
limb without passing through trunk may
cause only burning of limbs
• Often path involves arms to legs through
heart and lungs leading to fatal shock
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Shock Duration
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Net effect depends on duration
Short duration may give painful experience
@100 mA even few s of shock can be fatal
Remember light duty portable drill draws
about 3 A ( i.e. 30 times fatal current)
• High Currents for even appreciable
duration lead to inevitable death
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Summary of Effects
• Current > “let go” threshold lead to collapse or
unconscious or death
• Duration greater than 5s lead to asphyxiation
and heart failure are the causes
• Current through chest, neck, head or respiratory
centres lead to respiratory failure by disruption
of nerve impulses associated with respiration.
Very dangerous as effect continues after
cessation of current flow
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Summary of Effects contd..
• Most dangerous effect – even fairly small current
flows through heart region
• Causes ventricular fibrillation resulting in death
with in minutes
• Asynchronous movement causing heart beat to
stop
• If large currents flow through heart – heart
activity stops immediately
• Secondary effect could be tissue damage and
damage to internal organs when current flows
through major portions of the body
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Causes of Electrical accidents
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Inadequate wiring
Exposed parts
Contact with overhead power lines
Defective or Inadequate insulation
Improper grounding of equipment
Overloaded circuits
Damaged Power tools or equipment
Static Electrification
Inadequate Protection to Lightning
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Causes of Electrical accidents
contd..
• Aggravated by
1. Inadequate training
2. Unsafe work environment
- wet work surfaces
- inclement weather
- toxic chemicals
- excessive noise
- flammables
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Accident Prevention
• Most Electrical Accidents are preventable
• Desirable prevention technique is to
eliminate or reduce Hazard at source
• De-energize and lock out equipment prior
to repair or inspection
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Accident Prevention Measures
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Other Measures Include:
Provide Proper Insulation
Guarding or Cordon off
Elevation of live wires at least 8’ above floor or
ground
4. Provide protection devices like GFCI
5. Ground both system and equipment
6. Provide proper safety labels or signs
FORE WARNED is FORE ARMED!
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Accident Prevention Measures
Contd..
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At Work Place :
Provide Proper Training
Use tools in good condition
Use proper wire and connectors
Avoid contact with overhead power lines
Maintenance carried out by qualified electricians aware
of lock out procedures
Provide written Instructions on Lockout and tagging
procedures
Avoid wet or damp conditions
Never work alone
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Harmonized Symbol
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Accident Prevention Measures
Contd..
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Install Safety Switch
Never use faulty or wet appliances
Never stack power points
Take care around water
Never throw water on electrical fire
Keep appliances away from water.
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Thank you
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