Electricity is a powerful force and it has the potential to cause harm or even death. Electrical hazards are the most dangerous threats workers can face. Working near an electrical hazard is dangerous and can cause fatalities.
Promoting electrical safety in the workplace is the best method to reduce electrical hazards. Fatality and injury statistics increase every year all over the world due to the dangers of electricity.
Electricity travels in closed circuits, normally through a conductor. But sometimes a person’s body an efficient conductor of electricity mistakenly becomes part of the electric circuit. This can cause an electrical shock.
An electrical hazard is a dangerous condition where a worker could make electrical contact with energized equipment or a conductor. From that contact, the person may sustain an injury from shock, and there is a potential for the worker to receive an arc flash (electrical explosion) burn, thermal burn, or blast injury.
Table of Contents
Hazards of Electrical Energy:
Hazards of electricity include:
- Electric shock
- Electric burns
- Fire and explosion
- Hazards due to electric welding and cutting.
- Hazards due to static electricity.
- Fall of lightning from the sky.
- Shock and burns are injury from direct contact.
- Injuries are possible without current flowing through body, e.g., burns due to electric arcs, radiations etc.
- Main protections are proper fuses, switch gears, circuit breakers, ear-things etc.
- Safety precautions are highly needed to prevent accidents due to electrical hazards.
Effects of electric current on the human body
|Current (50 Hz or c/s)
|Feeling or lethal incidence
|Paralysis threshold of arm
|Can not release handgrip and may be fatal
|Stoppage of breathing
|Fibrillation. Threshold 0.5%
|Heart action disco-ordinate (probably fatal)
|Fibrillation. Threshold 99.5% (5-second exposure)
|Heart and blood circulation may stop (usually fatal)
|Heart paralysis threshold (no fill fibrillation)
|The heart stops for the duration of the current passage.
|Not fatal unless vital organs are burned
Effect of Voltages:
- For our 50 c / s electric supply, the main danger limits of voltages are:
- 24 volts for children, and
- 60 volts for adults
- In wet condition these values decrease and depend on other factors also.
Electrical parameters of the human body at 50 Hz, dry condition
|I = V/R mA
- The table indicates that as voltage increases, body resistance decreases, and current increases.
- Body resistance becomes partially zero at high voltages.
How to prevent electrical hazard accidents
A safe distance from electric lines:
- It is obvious that electric overhead lines should not be allowed in a place where the public or public vehicles have to pass through most of the time and not at such a low or unsafe distance (clearance above ground) so that chances of touching the lines may increase.
- Therefore some minimum safe distance from lines is necessary.
Capacity and protection of conductors, joints, and connections:
- All apparatus and conductors should be of sufficient size and strength. They should be covered with insulating material and placed or enclosed to prevent danger. Viz.
- Conductors in conduit
- Conductors in flexible metallic tubing
- Conductors in metal trunking
- Conductors with metal sheeting
- Cables in the trench.
- Electrical joints and connections should be of proper construction as regards conductivity, insulation, mechanical strength, and protection.
Means of cutting protection:
- Danger from excess current due to overload or short-circuit should be prevented by providing: 1. fuses 2. circuit-breakers or 3. thermal protection.
- The protective apparatus should be set at a low current value. Where time relays from over current protection are introduced as in the case of motors etc., a possible excessive rise in equipment and conductors should be considered.
- The number of items collectively protected should be limited to avoid over-fusing to withstand heavy switching currents.
- Fuses, relays, and circuit breakers should be of sufficient breaking capacity to operate safely at short circuit currents.
Earth fault protection:
- All non-current carrying metal parts of electric equipment should be earthed. Such parts are:
- Metal conduits, bus bar, steel trunking, and cable sheets.
- Non-current carrying metal parts of
- Switchgear fuse and starters
- Generators and motors
- Lighting fittings and
- Other electrical equipment or appliances
Earth insulation and continuity tests:
When an electric current passes through its expected distance (load) path. Its energy is utilized in heating, rotating, or doing the required function. But when due to insulation failure, breaking, opening, or loosening of conductor or directly touching to any metal part, tool, or human body, the current passes through the line of least resistance i.e. instead of passing through its regular machine or equipment circuit, it jumps (diverts) to the metal part or human body and tries to flow through the lowest resistance to the lowest potential.
- Now the earth has an extremely low electrical resistance and practically zero voltage, the leaking current (i.e. earth or fault current) tends to flow the metal part or the human body to the earth if they are touching the earth. If the human body is separated or insulated from the earth by insulating materials like rubber gloves, rubber shoes, rubber mat, wood, etc., the current will not flow through the body and the shock can be avoided. Similarly, the metallic exposed part if not earthed, will remain life and if someone touches it or metal contact between the exposed part and the earth is available, the current will flow to the earth.
- From a safety point of view, if a metal part of the equipment, machine, vessel, structure, pipe, etc. are in advance, properly earthed i.e., connected by an ear-thing conductor to the earth pit of low resistance, the accidental earth fault current will flow through it.
- Besides earth tests, it is also necessary to carry out insulation and continuity tests of installations and apparatus at periodical intervals. This is necessary to ensure that insulation values are within safe limits and that there is continuity of the circuit without excessive leaks. These can be carried out easily with special types of instruments.
- Ear-thing means a low impedance return path of the fault current. Actually the earth, now, rarely serves as a part of the return circuit but is being used mainly for fixing the voltage of system neutrals. The earth connection improves service continuity and avoids damage to equipment and danger to human lives.
- Earthing of a current carrying conductor is known as system earthing, while that of a non-current carrying conductor or metal work is known as equipment earthing. The former is essential to the security of the system and the latter to the safety of persons, property, and animals.
Protection against Surges and Voltage Fluctuation:
- When equipment is switched on, momentarily initially excessive currents are known as current surges.
- Surges may be more in starting cold circuits than the hot circuit i.e. restarting of the previously live circuit which was closed for a short while. For example, when large banks of filament lamps are switched on, a current surge arises, because they have much lower resistance when cold than when hot. If a live lamp circuit is made off and soon reenergized, it will face fewer surges.
- Therefore fuse or circuit breaker rating should consider this surge phenomenon.
- This is a common phenomenon. Supply voltage goes down resulting in reduced speeds of fans, motors, machines, etc. Again it comes and stabilizes the condition.
- Such voltage fluctuation, if on the higher side, may blow fuses or protection, and if on the lower side, reduces the productivity or effect of equipment.
- Automatic voltage regulators or voltage stabilizers either built-in with the equipment or external are readily available.
- Voltage fluctuation on either side is harmful. It accelerates or decelerates the speed of the machine.
Hazards arising out of ‘borrowed’ neutrals:
- In borrowing of neutral by tapping or otherwise, hazards arise if the size of the neutral conductor is changed in a new line or any discontinuity is left somewhere or if that line becomes the return path of normal load current.
- The hazard arises when there is a discontinuity in the neutral path. Therefore no disconnecting devices should be installed in the common neutral. In no case, the earth or buried metallic piping system should be used as the only path for the return of normal load current.
Lock out and tag out:
Lockout and Tag out procedure is also required to prevent accidents from unexpected starting or operation of any switch, starter, motor, equipment, etc. The procedure of lockout should include:
- Before locking or tagging, inform the concerned operators and users that line, switch, valve, or equipment will be isolated or de-energized and give them time to complete or stop their work.
- Plan the shutdown and make the system off.
- Insert lock and attach tagging.
- Test that the isolation is positive and as per expectation.
- When repair/maintenance work is over, open the locking or tagging.
- Again inform the concerned people that locking/tagging is removed and they can work as usual.
- The purpose of a lightning arrestor is to attract lightning from the sky and bypass it into the ground and not allow it to pass through any combustible material.
- A pole-type long rod of the good conductors is attached to the tallest structure at the site. Because of its good conductivity (low electrical resistance) electrical current of the lightning is directly passed into the earth. It is necessary to check the continuity and resistance of the lightning arrestor at regular intervals.
- It is not desirable to attach a lightning arrestor directly to the metal tank of flammable liquid or gas because in case of unknown discontinuity, lightning may pass through the metal surface and the whole tank may trap in the fire.
Capacity and protection of conductors, joints, and connectors:
All apparatus and conductors should be of sufficient size and strength. They should be covered with insulating material and placed or enclosed to prevent danger. Overhead trolley wires of cranes should be:
- Either protected by screen guards with suitable opening for tapping, or
- Insulated cable self-winding drums should be used.
Electrical joints and connections should be of proper construction as regards conductivity, insulation, mechanical strength, and protection.
Earth fault protection:
All non-current carrying metal parts of electrical equipment should be earthed. Such parts are:
- Metal conduits, bus bar, steel trunking, and cable sheets.
- Non-current carrying metal parts of
- Switchgear, fuse, and starters
- Generators and motors
- Lighting fittings and
- Other equipment or appliances.
Earth Leakage Circuit Breakers:
- where it is not practicable to obtain low impedance or where the protection afforded by the over current fuses and circuit breakers along with the earthed conductors is not adequate, leakage protection can be achieved by :
- Voltage-operated earth leakage circuit breakers
- Differential current circuit breakers or
- Combined voltage operated and differential current circuit breaker.
- The current operated ELCB operates even at 0.5 amp current and reduces fire risk. For further safety special 4-pin plug and socket and a core flexible cord are available.
No load protection:
- Employ trained electricians and give them full information regarding the possibility of arcing from fuses.
- Handles of switch or fuse box should be installed. Leather hand gloves (up to the elbow) should be given to workers.
- No load protection and protection against accidental contact are also necessary. At no load, no more current is desired. Therefore low current rated fuses are to select.
- The fuse box cover should have a small aperture to introduce the end of a voltage tester to ensure that the contacts are live or not. The box (flash proof) cover should be such that when it is opened, it will stop the current.
Control of hazards due to static electricity:
- As rubber is a bad conductor (a good insulator) of electricity, it accumulates static electricity to a high degree. Fires in the rubber industry are mostly due to the discharge of such heavy static charges.
- If equipment is not grounded, the static charge will continue to accumulate on it till it will discharge as a spark. Therefore grounding by a steel plate, and copper wire is necessary.
- Lightning from the sky is nothing but a discharge to the earth of enormous static charges generated and accumulated between the layers of air and clouds in the atmosphere.
Some specific static electricity hazards:
- Shock if the spark is not generated and the charged surface (not grounded) is touched by the human body.
- Fire or explosion if the spark is generated due to discharge of static charge into the flammable atmosphere.
- Readings are distorted or changed in sensitive instruments.
- Dust deposition on charged surfaces.
- Clogging or obstruction to the free flow of powders in chutes, silos, or hoppers.
Control of static electricity:
- Prevent charge generation.
- If this is not possible, prevent its accumulation.
- If this is also not possible, prevent discharge from being hazardous, and
- Prevent the formation of the flammable atmosphere near the possibility of static electricity.
- Mostly step – 1 is not possible but a step – 2 can be implemented effectively by ensuring ear-thing. For step – 3, the diameter of the pipe/hole is increased, and the flow rate is decreased.
General safety tips for working near electricity:
- Proper ear-thing and double ear-thing. General ear-thing for big power station, up to 0.5 ohms, big substation 1 ohm, small sub-station 2 ohm and tower and other places up to 8 ohms. Due to minimum ear-thing resistance, leakage current passes through it and not through a person. The earthing should be inspected, tested, and maintained properly. There should be a regular practice to check ear-thing. The minimum voltage between the ground and the earth wire should be 30 V.
- Use of appropriate insulated tools, rubber mats, shockproof gloves and boots, tester, fuse puller or tong, discharge rod, safety belt, hand lamp, wooden or insulated ladder and not wearing metal rings, etc.
- Always use ladders made with non-conductive side rails when working with or near electricity or power lines. Example: fiberglass.
- Ground fault circuit interrupters (GFCI) are required on temporary electricity and wet locations.
- Switches on the live line. Fused switches and air-current breaks should be used.
- Avoid temporary wiring. Avoid hurry and chance taking. Avoid left-hand touching.
- Maintain a 10 FT clearance from all overhead lines.
- Employ qualified and trained electrician.
- Low voltage (24 V AC or 110 V DC) in hazardous areas.
- Treat all electrical wires as if they were energized.
- Good insulation and tested wiring.
- Isolation of machine/equipment before use.
- Follow the Work-permit system.
- Safety tags and warning notices are to be provided.
- Use of machine/equipment within their limits i.e. no overloading.
- Place of oil-type transformer outdoor.
- Auxiliary room, battery room, and control room to be separated.
- Two exits in each electric room.
- Don’t touch notice on high voltage electric panel board.
- Precautions against thermal and mechanical stress, moisture, dust, and over-voltage. Automatic voltage regulators and overvoltage relays protect from overvoltages.
- Guard on transmission lines to prevent fault due to birds.
- Vermin proof (collective name of insects) enclosure for indoor switchgear.
- Use of electric shock guard (ELCB) and 3-pin plug and socket to have a proper earth connection.
- Use of reactors or current limiting impendence or underground neutrals or reduce fault levels.
- Use protective relays, circuit breakers, and rated fuses to control the current and isolate the faulty equipment speedily and automatically.
- Recording 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 armored cables.
- Generators and motors with fireproof doors are automatically actuated by fire detectors.
- Ready CO2 type and other fire extinguishers.
- Double communication systems with critical areas.
- Clear approach available for fire fighting squad.
- Flame and shock detectors and a central fire announcement system for fire safety.
- Diesel pump set for required fire water pressure.
- Good housekeeping including good maintenance of all electrical installations.
- Adequate working space and means of access around each apparatus.
- Allow only Qualified and competent persons to perform electrical work.
First aid for electric shock
- The victim usually gets stuck to the source of the electricity, and it is important that you first separate him from the electrical source.
- Turn off the power supply switch and disconnect the plug. It’s best to simply turn off the main power supply or pull out the fuse. Often, simply turning off the switch may not stop the flow of electricity.
- In certain circumstances, it may be quicker to simply pull the victim away from the electrical source.
- Do Not touch the victim with your bare hands, or the electric current will pass through you as well.
- If you are barefoot, stand on some clothes or any non-conductive material like wood or paper. Make sure you are not standing on anything that is wet.
- Throw a blanket over the victim and try to separate him from the source. Make sure you don’t touch him though. You could also use dry, nonconductive material such as a wooden broom handle or a chair to separate the victim from the live current. whatever is handy.
- Once the victim has been separated, check to see if he is breathing. If breathing has stopped or seems slow, administer CPR immediately.
- Let his head be slightly lower than the rest of the body, and raise his legs.
- Cover the victim with a blanket.
Electrical hazard sign and symbol:
Electrical hazard signs or symbols warn workers or other people about the electrical hazards or warn them serious injuries can occur from electric shocks and burns etc. The electrical hazard signs and symbols are found in workplaces such as construction sites, industries, electric power plants, power grids, or where high voltage electrical equipment is available.
The pictograms are universal but the color and text of the symbol may vary. Actually, these hazard signs work and prevent accidents by reminding the workers to wear appropriate personal protective equipment and take other necessary steps to stay safe.
Faq’s for Electrical hazard?
Which of the following are electrical hazards?
Some electrical hazards are given below:
1. Electric shock
2. Electric burns
3. Fire and explosion
4. Hazards due to electric welding and cutting.
5. Hazards due to static electricity.
6. Fall of lightning from the sky.
7. Interaction with overhead power lines,
8. Wet conditions.
What is electrical safety?
Electrical safety means the safety from the dangers of electricity. It is said that till we observe the legal provisions and norms it behaves like a good and humble servant of the people. As soon as the provisions are violated, electricity behaves like a monster and causes mishaps like accidents, fire, and explosions, etc resulting in the loss of human lives and property.
What are the reasons for the electrical accidents?
1. Premature failure of electrical equipment.
2. Lack of knowledge of electrical hazards and their safety.
3. Poor performance of protective devices.
4. Lack of presence of mind.
5. Poor workmanship.
6. Poor or lack of provisions for safety devices.
7. Avoiding the safety provisions for short time gain, etc.
When does electricity become hazardous to humans?
When it completes a circuit in the body it becomes dangerous. Current traveling from arm to foot is likely to go through the heart, making it more dangerous than current traveling between a leg and the ground.
Effects of electrical current on the human body:
1. Current flowing through the heart causes fibrillation of the heart.
2. Current flowing through muscles causes contraction of the muscles.
3. Current flowing through the brain causes a loss of consciousness and seizures.