Electricity is a powerful force and it has the potential to cause harm or even death. An electrical hazard is one of the most dangerous threats workers can face. Working near an electrical hazard is dangerous and it can cause fatal. 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.
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 lightening 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 human body
|Current (50 Hz or c/s)||Physiological phenomenon||Feeling or lethal incidence|
|1-3 mA||Mild sensation|
|3-10 mA||Painful sensation|
|10 mA||Paralysis threshold of arm||Can not release handgrip and may be fatal|
|30 mA||Respiratory paralysis||Stoppage of breathing|
|75 mA||Fibrillation. Threshold 0.5%||Heart action disco-ordinate (probably fatal)|
|250 mA||Fibrillation. Threshold 99.5% (5-second exposure)||Heart and blood circulation may stop (usually fatal)|
|4 A||Heart paralysis threshold (no fill fibrillation)||The heart stops for the duration of the current passage.|
|5A||Tissue burns||Not fatal unless vital organs are burned|
Effect of Voltages:
- For our 50 c / s electric supply, 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 human body at 50 Hz, dry condition
|volt||Rohm||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
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 for 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 are necessary.
- Rules 77 to 80 of the Indian Electricity Rules, 1956 provides safety distances.
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 as to prevent danger. Viz.
- Conductors in conduit
- Conductors in flexible metallic tubing
- Conductors in metal trunking
- Conductors with metal sheeting
- Cables in 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.
- Protective apparatus should be set at low current value. Where time relays from over current protection are introduced as in the case of motors etc., possible excessive rise in equipments 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 safety 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
- Switch gear fuse and starters
- Generators and motors
- Lighting fittings and
- Other electrical equipment or appliances
Earth insulation and continuity tests:
When 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 material like rubber gloves, rubber shoes, rubber mat, wood etc., the current will not flow through the body and the shock can be avoided. Similarly metallic exposed part if not earthed, will remain live 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 safety point of view, if 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, 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 type 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 current carrying conductor is known as system earthing, while that of 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, 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 reducing speeds of fans, motors, machines etc. Again it comes and stabilizes the condition.
- Such voltage fluctuation, if on higher side, may blow fuses or protection and if on lower side, reduces the productivity or effect of equipment.
- Automatic voltage regulator or voltage stabilizer either built-in with the equipment or external are readily available.
- Voltage fluctuation on either side is harmful. It accelerate or decelerate speed of machine.
Hazards arising out of ‘borrowed’ neutrals:
- In borrowing of neutral by tapping or otherwise, hazards arise if the size of neutral conductor is changed in new line or any discontinuity is left somewhere or if that line becomes the return path of normal load current.
- 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 shut-down 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.
- Purpose of lightning arrestor is to attract lightning from the sky and to bypass it into the ground and not allowing it to pass through any combustible material.
- A pole type long rod of good conductor is attached on the tallest structure at 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 its continuity and resistance of the lightning arrestor at regular interval.
- It is not desirable to attach lightning arrestor directly on 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 into 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
- Switch gear, 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 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 possibility of arcing from fuses.
- Handles of switch or fuse box should be installed. Leather hand gloves (up to 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 selected.
- Fuse box cover should have 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 hazard due to static electricity:
- As rubber is a bad conductor (good insulator) of electricity, it accumulates static electricity to a high degree. Fires in rubber industry are mostly due to discharge of such heavy static charges.
- If equipment is not grounded, static charge will continue to accumulate on it till it will discharge as a spark. Therefore grounding by a steel plate, copper wire is necessary.
- Lightning from 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 spark is not generated and the charged surface (not grounded) is touched by human body.
- Fire or explosion if spark is generated due to discharge of static charge into flammable atmosphere.
- Readings are distorted or changed in sensitive instruments.
- Dust deposition on charged surfaces.
- Clogging or obstruction to 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 formation of flammable atmosphere near possibility of static electricity.
- Mostly step – 1 is not possible but step – 2 can be implemented effectively by ensuring ear-thing. For step – 3, diameter of pipe/hole is increased, flow rate is decreased.
General safety tips for working with near electricity:
- Proper ear-thing and double ear-thing. General ear-thing for big power station, up to 0.5 ohm, big sub station 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 ear-thing should be inspected, tested and maintained properly. There should be a regular practice to check ear-thing. Minimum voltage between ground and the earth wire should be 30 V.
- Use of appropriate insulated tools, rubber mats, shock proof 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: fibreglass.
- Ground fault circuit interrupter (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 overheard lines.
- Employ qualified and trained electrician.
- Low voltage (24 V AC or 110 V DC) in hazardous area.
- Treat all electrical wires as if they were energized.
- Good insulation and tested wiring.
- Isolation of machine/equipment before use.
- Follow Work-permit system.
- Safety tags and warning notices to be provided.
- Use of machine/equipment within their limits i.e. no over loading.
- Place of oil type transformer out door.
- 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 over voltage relays to protect from over voltages.
- Guard on transmission lines to prevent fault due to bird.
- Vermin proof (collective name of insects) enclosure for indoor switchgear.
- Use of electric shock guard (ELCB) and 3-pin plug and socket to have 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 to 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 fire proof doors 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 central fire announcement system for fire safety.
- Diesel pump set for required fire water pressure.
- Good house keeping including well 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 of 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 sing 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 are work and prevent accidents by reminding the workers to wear appropriate personal protective equipment and take other necessary steps to stay safe.
Which of the following are electrical hazards?
Some electrical hazards are given below:
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,
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 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.
6.Poor or lack of provisions of 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 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.