Chonnam National University - Laboratory Safety Management System

Dangerous Electricity

  Electricity is a convenient and pollution-free energy that is widely used in diverse fields of our lives such as houses, schools and offices.
  However, if used improperly, accidents such as electric shock or fire may happen due to the properties of electric energy.
  The types of electrical accidents or disasters can be divided into several categories.
  However, most common accidents caused by electricity in laboratories are electric shocks and electrical fires.

Electric shock
If a person contacts with an electric device being connected to a supply of electricity, he/she gets an electric shock and suffers burns or gets severely injured. Or, he/she dies.
- Impact of currents
  - A person feels nothing at very low current when electricity flows in his/her body. However, if the current increases, he/she can feel the current depending on the magnitude of the "size of the passing current x time."
    If the current exceeds a certain level, it will be very dangerous that he/she will suffer from pain, breathing stop, suffocation, or ventricular fibrillation.
- Electrical resistance of the human body
  - The size of the passing current depends on the electrical resistance (impedance) of the human body, and the resistance depends on the applied contact voltage. In the worst case, the resistance is about 1,000 ohms.
    It becomes dangerous if the resistance decreases, keep in mind that the resistance should be large when handling electricity.
- Impact by current carrying path
  - The impact of electric shock depends on the current path. If the current passes through or around the heart, the current will have an impact on the heart
    and it is more dangerous. It is called the heart current factor.

Electrical fire

A fire caused by electricity

Cause of fire
- An electric fire is caused by structural defects of electrical equipment, etc., careless use of electrical facilities, or non-compliance with safety rules.
  - Igniting surrounding combustibles due to the overheating of an electric heater or lighting fixture.
  - Igniting a cable sheath due to the overheating of wire
  - Overheating of electrical equipment such as motors and transformers
  - Short circuit, power leakage, static electricity
Ignition source of electrical fire
- Movable electric heaters such as electric stoves, electric irons, electric blankets, sterilizers, and welding machines
- Fixed electric heaters such as electric thermostats, electric incubators, ovens, electric dryers, and electric furnaces
- Electrical equipment such as distribution transformers, motors, generators, rectifiers, chargers, and circuit breakers
- Power distribution lines, lead-in lines, indoor lines, outdoor lines, cords, and wires
- Wiring equipment such as switches, knife switches, automatic switches, connectors, multi-outlets, and electrical metering systems
- Power leakage in connected galvanized iron sheets, connection areas of metal plats or pipes, woods contacted with high-tension wires
- Static electricity sparks due to rubber coaters, rollers, fluid in pipelines, powder friction, etc.

Cause of electrical fire

Short Circuit	When a cable sheath is peeled off or a nail/pin needs to be driven wire, the wire may be directly or contacted with a low resistance (that is, short circuit). In this case, explosion sound or spark occurs at the time of the short circuit and the shorting point melts. If there is a combustible material around the point, a fire breaks out. Or, the overheating of the wire causes a fire.
Power Leakage	If the insulation of electrical equipment or electrical wires are deteriorated or mechanically damaged, the electric current leaks to the ground through the metal body. This phenomenon is called power leakage. If a surrounding flammable material is ignited due to the power leakage, it is called an electric leakage fire.
Overcurrent	When a current flows through a wire, the heat, in proportion to the value of the square of the current multiplied with its resistance (I2 x R), is generated. At the time, if the current exceeding the allowable current of the wire continues to flow, the sheath will be deteriorated due to the wire overheating and will ignite. In particular, a vinyl cable has a more severe phenomenon.
Electric Spark	A spark is generated when an electric circuit is opened/closed or a fuse is blown. In particular, when a circuit is broken, a spark largely occurs. At the time, if there is a combustible material such as volatile vapor or dust, it will be ignited.
Insulation deterioration or carbonization	Most insulators of wiring are made of organic matters. Generally, if organic matters are hardened for a long time, its deterioration will cause the reduction of its insulation resistance. If they are heated in a place where the air ventilation is poor at a high temperature, they will be carbonized and become conductive. Under this situation, if the voltage is applied, the carbonization is progressively promoted due to the insulation of the current, and the organic matters burn by themselves or the surrounding materials cause a fire.
Overheating of connection parts	If the current flows under the condition that it is incomplete of the contact between wires or wire and terminal, surrounding insulation materials are ignited with the heat of the contact part due to contact resistance.
Static Electricity Spark	The static electricity caused by the friction of a material, etc. ignites its surrounding flammable material by the generation of flame during the electric discharge depending on its size.