ELECTRICAL HAZARDS

1. PRIMARY HAZARDS:

  1. Electrical shock
  2. Burns-    (i) Joules burns        (ii)Flash over burns
  3. Fire and explosions-spark, static electricity

1.1. SECONDARY HAZARDS:

  1. Persons falling from height
  2. Dropping of tools and objects

1.2. SIDE RULE:

            While working on any electrical equipment

  1. Switch off
  2. Isolate
  3. Discharge any static charges
  4. Earth the equipment for further safety

1.3. ELECTRICAL SHOCK:

Electric shock is a sudden and accidental stimulation of the man’s

Body nervous system by electric current.  Current will flow due to

Voltage difference.

1.3.1. SHOCK OCCURS:

            Shock occurs when the body becomes part of the electric circuit.  The current must enter the body at one point and leave at another point. It is the current, which is responsible for shock.

1.3.2. REASONS FOR SHOCK

Victim touches live conductor

Victim touches poorly insulated conductor.

Open wires and short circuit due to equipment failure

Static electricity

Lightning

1.4. CLASSIFICATION OF VOLTAGE AS PER INDIAN ELECTRICITY ACT 1956: 

Low voltage < 250 V

Medium voltage  250-650 V

High voltage 650V – 33000 V

Extra High voltage > 33000  V

1.5. EQUIPMENT EARTHING PURPOSE:

Safety of the personnel

Safety of the equipment

To reduce the strain on the system insulation

To eliminate the possibility of electrical flash over.

1.6. STATIONS EARTHING RESISTANCES:

a)         Major power stations -0.5 ohms

b)         Major substation – 1 ohm

c)         Other sub stations -2 ohms

d)         Distribution transformer stations -5 ohms

e)         Overhead line supports -25 ohm

1.7. DANGEROUS VOLTAGE VALUES:

            The values of dangerous voltage depend upon the resistance of the human body and the strength of current flowing through the body.  In general for Alternating Current at 50 Hz limits may be taken as 24 Voltage for children and 60 Volts for adults.

            For a body in wet condition the resistance is low and hence the current flowing through the body will be higher.  In this condition even lower voltage may be dangerous.

A) VALUES OF CURRENT:

A current of 15-20 mA prevents the victim from releasing his grasp and hence is called “Threshold of danger “.Flow of currents above 50-100 mA through human body is likely to be fatal.  AC current frequencies of 30 to 100 KHz current which can flow through the human body safely without causing any injury. 

At about one mega cycle per second electric shock ceases to occur and the injury caused is only that of superficial burns.

B) MUSCULAR CONTRACTION:

People are thrown out of electric circuits because of muscular contraction.  This happens when the current is >20 mA.

C) AVERAGE RESISTANCE OF HUMAN BODY:

Human body resistance in dry condition is a 100,000 ohms.

Human body resistance in wet condition is 1000 ohms

1.8. EFFECTS OF ELECTRICITY PASSING THROUGH HUMAN BODY:

            (AC 50Hz, 0-3 second contact)

a.         <1mA                           No sensation

b.         1-10mA                        Shock, no pain, can let go

c.         10-20 mA                    shock, pain, can let go

d          20-35 mA                     Shock , pain , one cannot release himself

e.         > 50mA                        All the above and can be fatal

NOTE: An electric current of around 10mA is safe for human beings About 100mA through the body could be fatal.

1.9. CAUSES OF ELECTRIC ACCIDENT:

Make shift arrangements

Tampering with electrical equipment

Poor maintenance

Poor design or installation.

1.10.  FACTORS AFFECTING ELECTRICAL SAFETY:

Voltage

Strength of current through the body

Resistance of the body

Duration of the contact with the circuit

The frequency of the current

The path of current through the body

Individual susceptibility

Environmental condition such as wet or dry 

1.11. PERSONAL PROTECTION EQUIPMENT USED FOR ELECTRIC WORK:

Tested electrical rubber gloves suitable for the applied voltage.

Rubber soled shoes

Tools with insulated handles

Safety belt when working at height

Use of safety glasses or face shields when arcing is probable.

1.12. SAFETY PRECAUTIONS WHILE WORKING ON STORAGE BATTERIES:

When making electrolyte for storage batteries, always pour acid into water gradually as the reverse procedure will create an explosion.

Suitable goggles and face shields should be used.

While stirring acid, glass rod must be used.

While batteries are on boost charge, exhaust fan must be kept ‘ON’ to evacuate the hydrogen gas evolved.

Smoking and use of matches or other open flames in battery room is not permitted.

During the battery maintenance work one should not touch both +ve and -Ve terminals simultaneously.

1.13. ELECTRICAL SAFETY PRECAUTIONS:

Obtain a work permit before starting work on electrical equipment.

Only authorized persons should carry out any maintenance work after following work permit procedures.

The length of cables used on any equipment should be kept minimum.  Cables should not be allowed to lie on walkways.

All power connections to electrical equipment should be through suitable 3 pin connections and body of the equipment should be properly connected to earth, while working on electrical equipment / circuits.

Wet hands and wet ground should be avoided while handling electrical equipment.

(NOTE: Use only approved devices with ISI certification)Cables, fuses and equipment should not be overloaded. 

1.14. POWER TOOLS USE :

Electrically operated tools should not be used in an explosive environment.

Power plugs, cables, guards etc. should be inspected before using the equipment.

  • While applying a portable electric drill or grinder on a work, secure the work properly by using a VICE or any other suitable means.

When power tools are used at elevated planes, the operator should    wear a safety belt with the lifeline tied to rigid structure at top.

When pneumatic tools are used, the air hose should be secured to prevent it from whipping.

  • The handles of power tools should be suitably insulated

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