Exercise 4. Read text A Classification of Fires

Fires are now classified into general groups (ABCD) according to the nature of combustible materials, the size and intensity of the fire and substances which are most suitable for their extinction.

	Class A. These are fires involving solid materials usually of an organic nature (compounds of carbon) in which combustion takes place with the formation of embers. Class A fires are the fires of ordinary combustible materials, such as wood, paper fabrics, upholstery, rubber and plastics. To reduce the temperature of the burning material the best method of extinction is cooling. The most common and the most effective extinguishing agent is generally water in the form of a jet or spray.
Class B. These are fires involving liquids or liquefiable solids. For the purpose of choosing effective extinguishing agents, flammable liquids may be divided into two groups: a) those that are extinguished with water; b) those that are not extinguished with water. Depending on liquid, the extinguishing agents include water spray, foam, vaporizing liquids, carbon dioxide and dry powders. Blanketing and diluting are the most suitable methods of extinguishment of these class fires.
	Class C. These are fires involving gases or liquefied gases, e.g. methane, propane, butane, etc. This type of fire is also best extinguished by blanketing and diluting. Water in the form of a spray is usually used to cool the containers, and foam can be used to control such fires.
Class D. These are fires involving metals, such as magnesium, titanium, sodium, potassium, zirconium. Extinguishing agents containing water are ineffective and even dangerous. Carbon dioxide, dry powders or sand are usually suitable for extinguishing class D fires. The best method of extinguishment is to remove oxygen from the surface of the molten mass by blanketing it with a special (for each metal) powder, which “inhibits”, or “breaks” a chemical chain reaction.

According to present day classification electrical fires are considered to be fires of class A, B, or D. Extinguishing agents shouldn’t be conductors of electricity. Water and foam are both conductors of electricity and shouldn’t be used on live electrical equipment, but in some circumstances an exception may be made in favor of spray from specially designed nozzles. It is not always possible to extinguish a fire without using the cooling effect of a large quantity of water. In such cases the equipment must be made electrically dead before jets of water are applied, in order to avoid the danger of shock.

Cooking oils fires, which have previously entered Class B, are today a new type of fires dealing with high temperature cooking oils (vegetable and animal) greases and fats. Fires of this class are effectively and safely fought by cooling and blanketing methods of extinction.

Exercise 5. Give examples of (a) combustibles of each Class of fires and (b) methods of their extinction. Use the models and suggested variants in the boxes.