Electric Hazards - How To Control Them

Electric hazards – How to control them.

Since electricity has become a familiar part of our life. And interestingly, we tend to overlook the hazards of electricity and fail to treat it with due respect. Electricity exposes us to electric shock, electrocution, burns, fires, and explosions. Electricity can pass through only conductors and human body is a good conductor.

Electric shock.

Electric current passes through a closed circuit due to a

potential difference which is measured in Volts. This potential difference is maintained between wires and the ground. These wires are known as live wires. The ground potential is always zero. A person gets an electric shock when he interrupts the current path and allows it to pass through his body. This can happen in any one or all of the following ways.

·         When he touches two live wires of a circuit

·         When he touches one live wire standing on ground

·         When he touches any metal body, which is a conductor, which got energised with electricity due to some problem

An electric shock can result in a slight tingling sensation to cardiac arrest. The effect depends on many factors as:

·         The amount of current flowing through the body

·         Duration of the current flow

·         The route the current takes through the body

·         Frequency of the current (Alternating current (AC) only has frequency and direct current (DC) does not. In our country the frequency of electricity is 50 Hz (Cycles per second)

Burns.

Burns are the most common shock-related injury. An electrical accident can result in an electrical burn, arc burn, thermal contact burn, or a combination of burns.

Electrical burns are among the most serious burns and require immediate medical attention. They occur when electric current flows through tissues or bone, generating heat that causes tissue damage.

Arc or flash burns result from high temperatures caused by an electric arc or explosion near the body.

Thermal contact burns are caused when the skin touches hot surfaces of overheated electric conductors, conduits, or other energized equipment. Thermal burns also can be caused when clothing catches on fire, as may occur when an electric arc is produced.

Static electricity.

Static electricity can build up on the surface of an object like polyester saris. This static electricity can discharge to a person under right conditions and cause a shock. Another example is getting an electric shock while touching a car door handle on a cold, relatively dry day. This shock is not as potentially dangerous as normal electricity shock. In work places, with handling of plastic pipes and the like, static electricity can discharge over flammable or combustible materials and can cause explosion. Proper grounding (earthing) and other measures are required to prevent this.

Most of the electrical accidents happen due to the following factors:

·         Unsafe / faulty equipment or unsafe installation

·         Unsafe environment

·         Unsafe act / work practices

Following are some ways to prevent electrical accidents.

·         Use of insulation

·         Guarding

·         Grounding (earthing)

·         Electrical protective devices

·         Safe work practices

Insulators.

Use of insulators such as glass, mica, rubber, pvc, etc are used to cover conductors. These insulators must be suitable for the operating voltage of the system and must withstand environmental impacts. The insulation of wires and cables are colour coded as follows.

For single phase AC supply: Red – Phase, Black – Neutral, and Green – Earth (Ground)

For three phase AC supply: Red, Yellow, and Blue – Three phases, Black – Neutral, and Green – Earth

For DC supply: Red – Positive, and Black – Negative

Guarding.

Guarding involves locating or enclosing electric equipment to avoid people coming into contact with live parts accidentally. Appropriate cautionary signs must be placed at the entrances of electric rooms and guarded locations to alert people and forbid entry to unauthorized people.

Grounding (Earthing).

Grounding is intentionally creating a low resistance path for the current to flow into the earth. This prevents build up of voltages and thereby prevent electrical accident. Though it substantially reduces the risk, there is no guarantee that persons will not get a shock, or injured, or killed by an electrical accident.  

Protection devices.

Fuses are meant for short circuit protection and overload relays are for over current protection. Now MCBs (miniature circuit breakers) are available which combine both short circuit and overload protection.

ELCBs (Earth leakage circuit breakers) are available to protect from shocks. They are available with three sensitivity ratings: 100 mA for domestic applications, 100 mA and 300 mA for industrial applications.

Safe practices.

Refer my earlier post “Safety code – Electrical”