Electrical Safety - Hazards & Accident Prevention

 

INTRODUCTION

Accidents due to unsafe handling of electrical equipment, although contribute a very small percentage of the total compared with other agencies like machine tools, material handling equipment, hand tools, etc. have mostly a significant role to account for severe damage to person for property. Electrical energy, which acts  like our friend and servant when safely used, may become our master and killer if adequate precaution is not taken in its use.

Electrical hazards are generally of the following in nature :

a) Shock

b) Burn

c) Fire

d) Explosion

e) Arc-eye

 

a) SHOCK

When current passes through our body completing a closed circuit, excitation of our muscular and nervous systems occur and we perceive a shock. Shock is not always painful  but usually so. Current of varying  magnitude produces different type of injuries to human body. Ten mill amperes current is considered as the threshold limit for sensible shock. As the value  increase, various physical repercussions start in our body.   They are  muscular contraction, unconsciousness, asphyxiation, temporary paralysis, hemorrhage – all accompanied with pain which ranges from moderate to extreme in nature. At a  current value of 50 mill-amperes or more, the victim may die (electrocution) when his heart stops functioning because of interference of rhythmic function or heart by passage of current.

 

 Severity of Shock

 Severity of shock depends upon the following features :

a) Amount of current

b) Duration of flow of current

c) Path of flow of current

d) Type of energy (AC/DC)

e) Frequency ( in AC only)

f)  Environmental condition

More amount of current means disastrous effect. Current flowing through our body  in turn depends on the supply voltage and resistance of our body at the particular moment. According to Ohm’s Law , 1 = V/R, which means that flow of current (I) will be more at a higher voltage (V) or at a lesser resistance ® of the victim’s body. Human body resistance varies with a wide range being 25,000 to 6,00,000 Ohms with perfectly dry skin.  Resistance comes down to 1,000 Ohms  or even to 500 Ohms with wet skin when the victim receives severe shock.

Severity of injury is directly proportional to the duration of flow of current. If the current passes through the vital parts of a victim’s body like brain, lungs, kidneys, etc. the effect will be more disastrous rather than when it flows through non-vital parts of his body.

With alternating current (AC) the effect of shock  is always more than with direct current (DC). Shock with lower frequency of current is more dangerous than with higher frequency. 50 cycles per second (50 Hz) is considered as unsafe frequency. If current, at higher frequency is generated and used, as in the case of high frequency induction furnace, etc., it is considered relatively safe. At about 1,000 Hertz frequency, shock reduces considerably.

The person receiving shock will face severe injury if his surrounding atmosphere (environmental condition) is wet or humid or if the sweats or gets drenched with water when his body resistance will come down abruptly to a very low value.

 

b) BURNS

The thermal effect of current causes burn injury. The heat developed due to passage of current is directly proportional to the square of the current, resistance of our body and the period of flow of the current. Sufficient amount of heat is thus development in no time and causes burn injury. Direct contact with line or exposure to high flash resulting from defective equipment causes such burn injury. Short-circuiting of cables, switches, etc. may produce such flash of explosive violence.

 c) FIRE

 It occurs due to either of the following faults in electrical equipment.

a) Short-circuiting

b) Over loading

c) Loose connection

Short-circuiting occurs  when, in the single phase circuit, phase line touches the natural line or in 3-phase circuit one phase touches the other as a result of failure of insulation of cables, wires, or conductors. Overloading means drawing of more current by any equipment  than its rated capacity which occurs due to failure of insulation in the winding of any equipment. Loose connection means formation of are at junction points of cable or at the terminal points of cables and fitting. 

In all the above three fault conditions heat is generated in the conductor or wire which in turn heats up the insulating materials (PVC, rubber, etc.) of the conductor or wire to catch fire. 

Basic causes of electrical fire are improper maintenance of earthing system, use of oversize fuse and failure of insulation.

d) EXPLOSION         

Explosion in an electrical equipment occurs when fire due to short circuit originates in a confined space filled with oil like tank of oil circuit breaker or transformer, etc.

 

e) ARC EYE         

Irritation of eyes occurs to an electric-arc welder who does not use protective glass for welding. Ultraviolet invisible rays from the are affects the eyes of the welder causing swelling, pain, etc. which automatically gets cured within two days or so. The use of a welding screen with proper shade number glass will be guard against such arc-eye.

 

ACCIDENT PREVENTION

Accidents due to  shock, burn, fire explosion, etc. may be averted or severity reduced by the following two techniques.

1. Proper Maintenance

Any possible breakdown or fault should be anticipated be experienced personnel and adequate preventive measures should be taken before hand. A checklist should be prepared for periodic and special inspection of various installations. When doing preventive maintenance, the following points should be given emphasis.:

a) Checking of equipment earthing,

b) Checking of insulation of cable, wire, conductor, etc

c) Checking for loose connection of wires/cables and fittings.

Equipment earthing means connecting metal casing / parts of electrical equipment to good mass of earth under permanent moisture level through low resistive metallic path. Efficiency of earthing depends on the resistance of earth continuity conductor, earth electrode, contact resistance of the electrode with surrounding soil and specific resistance of the said soil. To ensure sound ear thing, system should be periodically inspected visually for broken earth conductor for maximum permissible earth loop resistance for a particular load.

Proper earthing takes care of accidents due to shock, burn, fire etc. by ensuring immediate discharge of current from the metal parts of a faulty equipment into the earth. It also helps the circuit protective device like fuse to work promptly by allowing sufficient amount of current to pass through it in case of a fault.

Insulation of wires or cables get damaged by mechanical agencies, chemical, oils or weathering effect. They are to be inspected visually for such damage and replaced in time to prevent accidents due to shock, fire etc. Insulation resistance test by instrument is recommended where visual inspection for insulation failure cannot detect such fault.

Various circuit protective devices like fuse, relays, release coils, etc. are required to be checked for protection of equipment against faulty condition which may otherwise lead to accidents causing fire.

2. Compliance with Safety Rules

Safety Rules are to be observed at the various stages of designing, fabricating, installing, operating and maintaining of  electrical equipment. A few of the important safety rules are :

a) Follow Competency of Personal – Until a person is competent enough with full knowledge and experience of electrical work, he should not handle any electrical breakdown work.

b) Do Interlocking Design – Equipment should be designed, as far as possible, with interlocking arrangement in such a way that unless supply is cut off live parts should not be accessible and conversely until the live parts of an equipment is guarded accidental touching, the equipment cannot be energized.

c) Design for Low Voltage – Wherever possible, for portable equipment a low voltage supply should be used with separate busbar.

d) Treat Unknown Circuit as Live – Until and unless or a line is definitely known as to be dead, it should be treated as a live circuit or live line.

e) Do Electrical Locking – When attending any breakdown with deadline, the control switch should be locked, fuse grip should be removed and the key of the lock should be retained with the men attending to breakdown.

f) Follow Work Permit System – for attending any electrical work, which is usually dangerous, Permit to Work System should be followed.

g) Use Standard Fittings and Accessories – Use of substandard fittings and unsafe accessories should be discouraged.

h) Wear/Use Personal Protective Equipment – Suitable PPE like non-conductive helmet, leather gloves, electrical safety shoes, etc. should be used as and when necessary.

i) Get Emergency Training – Persons working in electrical field should have training on fire fighting, emergency signaling, first aid in addition to his normal operational training.

j) Fencing of Live Conductors – Charged line running exposed without insulation should be installed at sufficient height (minimum 8.5 ft. from working level) and guarded against suitable barrier or fencing to prevent accidental touching.

k) Follow Do’s and Don’s - For any special work or risk area, special safety instruction  in the form of Dos and DON’Ts  should be displayed e.g. in substation, receiving or sending ends of distribution lines.

l) Discourage for Makeshift Arrangement – Temporary wiring and work without proper accessories (e.g. plug earth connection) should be discouraged to avert accidents due to shock, fire.

Thank You for reading the page. Please follow the blog for information on Safety Jobs, Industrial Safety, Fire Safety and Construction Safety courses study material.

Visit and subscribe our YouTube channel Being Safety Officer for safety videos.