Portable extinguishers:types

The colour codes for each type of appliance are as follows:
Red for water.
Cream for foam.
Black for CO2.
Blue for powder.
Green for halon (BCF).
Figures 2.12a–c show various types of extinguisher. Although older fire extinguishers are colour coded, new ones are all red in colour with labelling to identify their contents and applications.
Water
Water is the most widely used extinguisher agent. With portable extinguishers,a limited quantity of water can be expelled under pressure and its direc- tion controlled by a nozzle.
There are basically two types of water extinguishers. The gas (CO2) cartridge operated extinguisher,when pierced by a plunger,pressurizes the body of the extinguisher,thus expelling the water and producing a powerful jet capable of rapidly extinguishing class A fires. In stored pressure extinguishers the main body is constantly under pressure from dry air or nitrogen,and the extinguisher is operated by opening the squeeze grip discharge valve. These extinguishers are available with 6 litre or 9 litre capacity bodies and thus pro- vide alternatives of weight and accessibility.

Foam
Foam is an agent most suitable for dealing withflammable liquid fires. Foam is produced when asolution of foam liquid and water is expelled underpressure through a foam-making branch pipe atwhich point air is entrained,converting the solution into a foam.

Foam extinguishers can be pressurized either bya CO2 gas cartridge or by stored pressure. Thestandard capacities are 6 and 9 litres.

Spray foam
Unlike conventional foams,aqueous film forming foam (AFFF) does not require to be fully aspirated in order to extinguish fires. Spray foam extinguishers expel an AFFF solution in an atomized form which is suitable for use on class A and class B fires. AFFF is a fast and powerful means of tackling a fire and seals the surfaces of the material,preventing re-ignition. The capacity can be 6 or 9 litres,and operation can be by CO2 cartridge or storedpressure.
Carbon dioxide
Designed specifically to deal with class B,class C and electrical fire risks,these extinguishers deliver a powerful concentration of carbon dioxide gas under great pressure. This not only smothers the fire very rapidly,but is also non-toxic and is harmless to most delicate mechanisms and materials.
Dry powder
This type of extinguisher is highly effective against flammable gases,open or running fires involving flammable liquids such as oils,spirits,alcohols,solvents and waxes,and electrical risks. The powder is contained in the metal body of the extinguisher from which it is supplied either by a sealed gas cartridge,or by dry air or nitrogen stored under pressure in the body of the extinguisher in contact with the powder.

Dry powder extinguishers are usually made insizes containing 1 to 9kg of either standard powder or (preferably and more generally) all-purposepowder,which is suitable for mixed risk areas.

Vaporizing liquid (halon 1211, BCF)
Portable extinguishers of this type are manufactured in sizes ranging from 1 to 15kg. They areparticularly effective for dealing with class B firesand with fires started by an electrical source.
Halon 1211 (bromochlorodifluoromethane,BCF)has a low toxicity level,is considered to be noncorrosive and has a long storage life. It is clean touse and leaves no residue,thus rendering it harmless to delicate fabrics and machinery. However,owing to the contribution of halons to atmosphericozone depletion most companies have decided tocease production of halon 1211.

Choosing and siting portable extinguishers
Because there is such a variety of fire risks in bodyshops,it is important to analyse these risks separately and (with the help of experts such as fireofficers) to choose the correct fire fighting medium to deal with each possible fire situation. It should be noted that portable fire extinguishers are classified as first-aid fire fighting and are designed forease of operation in an emergency. It is importantto realize that because they are portable they haveonly a limited discharge. Therefore their siting,together with an appreciation of their individualcharacteristics,is fundamental to their success infighting fire (Figure 2.13).