HAZ of Elec
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Transcript of HAZ of Elec
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ELECTRICALSAFETYPresentation by:
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Causes o f ELECTRICAL HAZARDS
Can be div ided into three main g roups
Power Electricity
Static Electricity
Lightning
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W hat are we going to discuss?Hazards caused by Power Electricity
Major factors governing electrical hazards
Broad classification of electrical accidents
Portable electrical tools
OH & UG Distribution
Major factors causing electrical
accidents
Basic points to be observed
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FACTORS GOVERNING
ELECTRICAL HAZARDS
1. Amplitude & duration of current
2. Condition & position of the body
3. Ambient temperature & humidity
4. Oxygen & CO2 content in air
5. Flooring condition
6. Condition of EARTHING
7. Sex & age of the person
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HEARTis the best pump designed by nature
..in the average life span of 70 years, pumps two
million liter of blood, by beating 2500 million times!
......can not withstand 150 mille Amp current for more
than one second. It can cause death. Controlled
shock is used to revive heart.
.....if fresh blood is not supplied to brain for
more than THREE minutes, death can occur.
.... of human beats @ 68 to 70 times / minute
of elephant beats 25 times / min
of mouse beats 700 times / min
of parakeet beats 1000 times/ min
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EFFECT OF CURRENT
ON HUMAN BODY50 Hz A..C. passing thro body for 1 second, through
the route - left hand to both feet to earth.
upto 1 mA No sensation
1 mA to 8 mA Sensationbut not painful8 mA to 15 mA Painful shock
15 mA to 20 mA Muscular control lost
20 mA to 50 mA Severe muscular contraction
50 mA to 200 mA Ventricular fibrillation
possible death
Above 200 mA Severe burnsSevere
Ventr.fibrillation.- Heart arrest
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Condition Positionof the body
Dry skin offers 100,000 to 600,000
ohms resistance
Wet skin offers only 1000 ohms resistance
There are various postures of body, during which
a person gets electric shock. The most dangerous
position is the one, in which current passes
through the heart in very short time / route.
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HEART CURRENT FACTOR
CURRENT PATH HCF
L. H. To left ft or right ft or both feet 1.0
Both hands to both feet 1.0
L. H. to R. H. 0.4
R. H. to left ft or right ft or both feet 0.8
Back to right hand 0.3
Back to left hand 0.7 Chest to right hand 1.3
Chest to left hand 1.5
Seat to L. H. or R. H. or both hands 0.7
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How to f ind ou t TVF ?
1. Threshold of Ventricular Fibrillation (TVF)
is different for different current routes
through the body.
2. TVF for any route = TVF for LH to both feet
HCF for that route ( ref. Table)
3. For the route of current from chest to left hand
TVF = 50 mA / 1.5 = 33 mA
This means that, when 33 mA current passes forone second from chest to left hand, ventricular
fibrillation is possible. For LH to both feet, this
value is 50 mA.
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AMB IENT TEMPERATURE
Higher More Wet Low
Ambient Perspiration body resistance
HUMIDITY
Higher Body does not Low resistance
Humidity get dried up
CO2 & O2 CONTENT IN AIR
Higher CO2 & lower O2 in the air, reduces
the resistance of the body.
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CONDITION OF FLOORING
1. Wet floor offers less than 100 ohms resistance
2. Insulated rubber mat offers more
than 10 million ohms resistance.
3. Dry, varnished wood was used
as support insulators in LT panels.
4. Wet wood can give path to
leakage current
5. Accidents in bath rooms are fatal , because
person with wet body is standing on the
wet flooring.
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CONDITION OF EARTHING
For earthing the equipment, there are many links
from equipment to the EARTH.
These are, Earth terminal ( of the equipment to beearthed ), Earth wire, Earth pin (in the plug ), Earthing
from the switchboard to Distribution Board, Earthing
wire from DB to the main Meter Box, from MB to
Earth pipe ( inserted in the earth )
Any weak link or discontinuity in the entire CHAIN,
will create unsafe conditions during Electrical
Accident
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CLASSIFICATIONOF
ELECTRICAL ACCIDENTS42 % # Abuse of equipments # Poor maintenance.
# Failure to switch off eqnt.(auto or manual)
31 % # Inadequate design & assembly # Unreliable
protection # Less clearance of live part from
the body # Too much critical design
27 % # Improper / unsafe workplace
# Inadequate / confusing instructions
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PORTABLE TOOLS
Check the condition of plug & socket
Do not use the tool, if casing is broken
Check the earthing connections at both ends
Cord should be sufficiently long, to reach
the workplace without tension .
No temporary joints
Never stand on damp surface whileoperating the portable tool.
Do check the tool at ground level before use.
Carry out preventive maintenance regularly.
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OH & UG Distr ibu t ion
Accidental charging of the line / equipment
Accidental back feeding of power
Crane / Tower ladder crossing OH line
Junction poles in the OH line network.Wrong identification of cables.
Charging the line without total checking
Wrong isolation of the circuit
Not using safety appliancesLack of Preventive Maintenance
Poor EARTHING
Corrosion of OH poles at the base.
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DOMESTIC USE OF ELECTRICITY-1
1. Do not let children play with electricity.
2. Maintain EARTHING healthy. Check it regularly.
3. Use 3-pin plug with earthing connected at both
ends.
4. Use fuse / MCB / switches of proper rating.
5. Temporary repairs are dangerous.
6. Give common knowledge of electricity to all
family members.
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DOMESTIC USE OF
ELECTRICITY-27. Do not repair electrical equipment without proper
tools & knowledge.
8. Do not carry out repair without isolating the
circuit / equipment
9. Never connect EARTHING with water pipe
10. Multiple tapping from one socket are unsafe
11 Be careful while washing floors & kitchen dado
12. Never operate electrical appliances with wet hands
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OFFICES & SHOPS
1. Wiring in the false ceiling
2. Switches at visible location
3. Positive isolation
4. Chokes of fluorescent tube lamps
5. High wattage lamps in the show case
6. Reliable earthing for the power system
7. Appliances like hot plate, elect, kettle etc.
8. Fire Protection & Smoke Detection systems
9. CO2 / Halon fire extinguishers at strategic
locations
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MAJOR FACTORSCAUSING ELECTRICAL ACCIDENTS-1
1. SHORT CUTS
2. POOR EARTHING
3. OVERCONFIDENCE4. HURRY TO COMPLETE THE JOB
5. NOT USING SAFETY APPLIANCES
6. WORKING WITHOUT CONCENTRATION
7. LACK OF PREVENTIVE MAINTENANCE
8. POOR KNOWLEDGE OF EQUIPMENTS
& SYSTEM
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MAJOR FACTORSCAUSING ELECTRICAL
ACCIDENTS- 2
9. POOR QUALITY OF TOOLS
10. UNSAFE WORKPLACE
11 MISCOMMUNICATION
12. TEMPORARY REPAIRS
13. UNTRAINED MANPOWER
14. IMPROPER / INADEQUATE PROTECTION
15. NOT FOLLOWING THE SAFETY PROCEDURE
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BASIC POINTS TO BE OBSERVED
Do not operate electrical equipments with wethands.
. Use of wet shoes & wet clothing is unsafe
Never connect earthing with water pipe
Maintain EARTHING in good condition.
Do not use water in electrical fires.
Use personal protective appliances
Temporary repairs are dangerous
Qualified / Trained personnel
Use ELCB.
No monkey tricks, please....
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CASE STUDIES - 1
Fatal accident to fitter
When 5100 KW motor did not trip.....
Fatal accident on 5 Amp socket
Flash over during ACB checking
Accidental start of 800 KW compressor motor
Accident during maintenance on 11 KV panel
Fatal accident due to cable TV wire.Street light ladder crossing 11 KV line
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CASE STUDIES - 2
Shock on a fridge
Accident during motor module maintenance
Fatal accident to painterAccident to lineman
Flash over during checking of lighting module
Accident while using voltmeterC. T. replacement in MCC module
Repairing table lamp in live condition
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CASE STUDIES - 3
Switching on OH main line.
Accident on the junction pole
Three phase switch of AC plant
Accident caused by back feeding of power
Fire in the power transformer of theatre
Earthing of bus side of OCB panel (SEC)
Taking towel hanged on flexible wire
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CASE STUDIES - 4
Cutting of wrong cable
Non-standard termination of two cables in
one straight joint
Local heating in HT panel (after maint.)
Flashover in 33 KV panel (BBP)
Wireman taking measurement with cotton tape
Opening of rear cover of HT panel...
Man replacing lamp without switching it off
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Remember....Electricity is the best servant,
BUT,
Tough taskmaster.
It does not tolerate any negligence,Penalties are heavy.
HENCE,
Treat Electricity respectfully.
Thank you