HAZ of Elec

8/12/2019 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

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HAZ of Elec