Classes of Fires
Fire has good and bad points. Under control, fire cooks our food and warms us on cold nights. When fire is not controlled, it can burn our houses down and do lots of damage to people and the environment.
In the workplace, fire is grouped according to what is burning e.g. wood, flammable liquid, combustible metals, etc. It is important for you to know about the different types of fires that could occur in the workplace. A fire underground can be very dangerous, so every mine should have a plan in case of a fire.
The origin or fuel type of the fire determines what we use to remove a specific element (leg) of the fire triangle. Thus, to ensure that the correct extinguishing agent is used on a given fire, fire has been divided into classes (categories).
The first thing to look at are the basic classes of fire or what is burning, each class has been given a “name” in the form of a letter of the alphabet eg: A, B, C, D, E
Class A Fires:
This is a fire where solids, such as wood, cloth, paper, rubber and plastics, burn.
Either quenching of cooling with water usually easily distinguishes this class of fire.
Class B fires:
These are fires involving flammable and combustible liquids. Both flammable and combustible liquids are fire hazards. If there is a flame nearby, they will catch fire and become extremely dangerous.
What is the difference between a flammable liquid and a combustible liquid?
Flammable liquids have a flashpoint below 61°C that is they do not have to become very hot before their vapours become dangerous and burn. Combustible liquids have a flashpoint of above 61°C – they catch fire at higher temperatures.
When fighting this class of fire, the exclusion by smothering is usually employed.
It should be noted that most of these products float on water and could lead to fire spreading if water was applied.
Class C Fires:
This type of fire involves electricity or electrical equipment. It needs special firefighting equipment to control it. This type of fire may be caused by Class A or B fires.
The reason for the separate classification is due to the fact that any extinguishing agent containing water cannot be used to fight a fire involving electricity.
Water is a conductor of electricity and could electrocute anybody trying to fight such a fire with water.
Class D Fires:
Class D fires are fires involving combustible metals, such as potassium, sodium, and magnesium. A specialist should be called in to put out these fires.
This class of fire is relatively difficult to extinguish, and only specialized equipment and powders are used. Standard equipment such as dry chemical extinguishers CANNOT BE USED as the force of the discharge power disturbs the surface of the burning metal (usually in the fine form such as scarf, cuttings, chips or powder), thereby intensifying the blaze.
Class E Fires:
This class of fire involves flammable gasses. Only CUTTING OFF THE GAS SUPPLY extinguishes flammable gas fires. Water should be used to COOL CONTAINERS and SURROUNDS.
Always consider the possibility of an explosion where gas in cylinders is involved.
