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Today's blog contains hazards related to Electricity, Factors governing electrical hazards, Safety equipment etc.

Blog contents

What is electrical shock? [ overview]

Factors governing electrical hazards

Factors leading to electrical shock

How to avoid electrical accidents?

1. What is electrical shock? [overview]

Electric hazard to human is due to Current not Voltage
Human body's blood is good conductor of current but skin is resistor at 10 mA range
Electrical shock to person refers to the current flowing through nerves, muscles and body organs.
Current produce heating in body and body parts got burns due to this.
AC current is more dangerous than DC current. AC current fibrillate at each cycle but DC does it once.

Hazards of Electricity

2. Factors governing electrical hazards

There are some factors which effect the injury to the person experiencing electrical shock

A. Amplitude of current
B. Duration of current
C. Condition of the body
D. Age & Sex
E. Temperature & Humidity.
F. Oxygen & Carbon dioxide content.
G. Material & flooring
H. Position of Hands and Legs.
I. Condition of earthing.

A. Amplitude of current

When 50 Hz current pass from body for one second it gives following effects

Upto 1 mA - No sensation
1 to 8 mA - Sensation without pain
8 to 15 mA - Painful shock.
15 to 20 mA - Muscular control loss, Result in sticking
20 to 50 mA - Severe muscular contraction
50 to 250 mA - Muscle damage [Ventricular fibrillation], Possible death
250 mA and above - Severe burns, severe ventricular fibrillation, Resulting in death for long shocks.
4A - Heart paralysis, Heart stops for duration of current passage for short shocks, For short shocks heart may re start on interruption of current
5A - Tissue burning.

[Note : This values are for alternate current, direct current is less dangerous]

B. Duration of current

Duration of current and its amplitude both are inter related in deciding the injury.
If current passes for longer time, body will absorb more energy and injury will be more.
10 mA current can flow for 5 seconds through body without any danger. While 5 A current for 1 Second could be result in fatal.

C. Condition of the body

Resistance by

Dry skin - 1 lakh to 6 lakh ohm
Wet skin - 1 thousand ohm

This is the reason wet skin conduct electricity faster and high risk of electric shock.

Current flowing through body can be calculated by Ohm's law
Current = [Voltage/ resistance of body] + resistance of flooring

D. Age & Sex

Electricity resistance - Men > Women > Children

E. Temperature & Humidity.

Higher Temperature and Humidity generates more sweat.
Sweaty skin increase conductivity of electricity.

F. Oxygen & Carbon dioxide content.

When person breath Carbon dioxide more his resistance to electricity.
When welder doing his job He has more risk of electric shock.

G. Material & flooring

Person standing on dry wooden block has less possibility of shock.
Electric shock possible areas - Bathrooms, Checker plate, Steel platform, Wet soil

H. Position of Hands and Legs

Position of body decides how current flows inside body.
When hand and legs position is that type where heart is in center is most dangerous.

I. Condition of earthing

Good and continue earthing has less possibility of accident.

3. Factors leading to electrical shock

Lack of knowledge, Overconfidence, wrong practice, Miscommunication.
Wrong risk taking, Working without Proper PPEs, Bypass Safety system or SOP
Jobs in hurry, working without concentration
Poor maintenance system, Equipment, Quality of tools. Temporary repairs, Poor earthing.

4. How to avoid electrical accidents?

Always wear rubber gloves and safety shoes with rubber soles It has resistance up to 20 Mega Ohms
Whenever any job taken Lockout must me done on paper duly signed.
Never bypass interlock without study and circulating information among all departments.
Grounding must be provided at 2 points.
Measuring instrument must be calibrated.

Install -

Earthing, Double Earthing and General earthing according to power station size.
Use of Switches, rubber mates, Wooden flooring, Wooden ladders and scaffolds, Fuse puller, Safety shoes with rubber soles.
Use Insulated cables
Earthing monitoring system
Emergency tripping switch
Earth leakage circuit breaker system installation
Replace damaged cables, improper plugs, loose connection,
Always use 3 pin plug.
Don't use multiple sockets in one socket.
Avoid temporary lighting.
Safety tags and warnings should be placed.
Overload and under load protection.
Auxiliary room, batter room, and control room must be separated.
Frequent inspection of Thermal and Mechanical stress, moisture, dust.
20. Use of reactors or current limiting impendences or underground neutrals to reduce fault levels.
Use protective relays, circuit breakers and rated fuses to control the current and to isolate the faulty equipment speedily and automatically. Check before closing an OCB for high voltage lines.
Use of grounding mat of low ohmic value and all non current-carrying parts to be connected to the grounding grid by duplicate earth and segregated non current carrying metallic parts to be electrically bonded.
Record of ground resistance values and the physical condition of the grounding mat. Temperature sensitive alarm and protective relays to make alert and disconnect equipment before overheating.
Interlocks to put into and out of service equipment correctly. Testing for high voltage, timing, polarity and insulation resistance.
Cleaning and application of silicon grease to insulators to reduce pollution deposits.
Safe cable trenches and preferably armoured cables.
Transformers with oil safety, D.O. fuse, L.T. fusc, MCB, MCCB and automatic fire protection system. Generators and motors with fire proof doors automatically actuated by fire detectors. 30.
Ready CO₂ type and other fire extinguishers.
Double communication systems with critical areas.
Clear approach available for fire fighting
Flame and shock detectors and central fire squad annunciation system for fire safety.
Diesel pump set for required fire water pressure.
Good housekeeping including well maintenance of all electrical installations.
Adequate working space and means of access around each apparatus.
First-aid boxes and respiratory equipment ready.
Training for artificial respiration to save life from shock.
Prevent higher humidity and temperature near electric installations. Work with full protection in raining.
Use of flameproof/explosion proof equipment in flammable/explosive areas.
Earthing and bonding of solvent carrying pipelines and equipment.

ELCB - Earth leakage circuit breaker
ELCB works before current reach at danger level it shut off circuit in mili seconds.

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Hazards of Electricity | Safety blog

Hello Readers

Blog contents

1. What is electrical shock? [overview]