Fire Fighting Procedure

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This Procedure describes the types of fire that may be encountered, together with the means of extinguishing fires.  
1.1 THEORY OF FIRE-FIGHTING
Fire requires a combination of fuel, oxygen, a source of ignition, and a continuous
chemical reaction, commonly referred to as combustion.
Fires are extinguished by the removal of heat, fuel or air, or by interrupting the chemical reaction of combustion. The main objective of fire fighting is to either reduce the temperature, remove the fuel, exclude the supply of air, or interfere chemically with the combustion process with the greatest possible speed.
1.2 TYPES OF FIRE AND APPROPRIATE EXTINGUISHING AGENTS
The classification of fires given below is that historically provided in ISGOTT and
conforms to the classifications used within the European Union (EU). Alternative
classifications may be used outside the EU.

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1.2.1 CLASS A - ORDINARY (SOLID) COMBUSTIBLE MATERIAL FIRES
Class A fires are those involving solid cellulosic materials such as wood, rags, cloth, paper, cardboard, clothing, bedding, rope and other materials such as plastic, etc. Cooling by large quantities of water, or the use of extinguishing agents containing a large proportion of water, is of primary importance when fighting fires involving ordinary combustible material. Class A materials can support deep-seated and smouldering fires long after visible flames are extinguished. Therefore, cooling the source and surrounding area should continue long enough to ensure that no re- ignition of deep-seated fires is possible.
1.2.2 CLASS B- FIRES INVOLVING FLAMMABLE AND COMBUSTIBLE HYDROCARBON LIQUIDS
Class B fires are those that occur in the vapor-air mixture over the surface of flammable and combustible liquids such as crude oil, gasoline, petrochemicals, fuel and lubricating oils, and other hydrocarbon liquids. Fires involving flammable gases are generally included in this classification. These fires are extinguished by isolating the source of fuel (stopping flow of fuel), inhibiting the release of combustible vapors or by interrupting the chemical reaction of the combustion process. Since most Class B materials burn with greater intensity and reignite
more readily than Class A materials, more effective extinguishing agents are
generally required. Class B liquids are generally divided into the two broad categories of non-volatile (combustible) and volatile (flammable) materials. This division is generally sufficient to ensure that proper precautions and measures can be specified for handling Class B liquids. In short, ‘non-volatile’ materials have a flash point of 60°C (140°F) or above, as determined by the closed cup method of testing. ‘Volatile’ materials have a flash point below 60°C (140°F), as determined by the same method. Flammable gases are volatile materials that typically exhibit flash points at temperatures at or below the ambient range and have relatively high vapor pressures, compared to flammable (volatile) liquids, when
in the liquid state. A liquefied gas, as referred to in the following text, is a flammable gas that has undergone a phase change to the liquid state by refrigeration or pressurization. Low expansion foam, defined and discussed in Section 5.3.2.1, is an effective agent for extinguishing most hydrocarbon liquid fires. It should be applied so as to flow evenly and progressively over the burning surface, avoiding undue agitation and submergence. This can best be achieved by directing the foam discharge against any vertical surface adjacent to the fire, both in order to break the force of discharge and to build up an unbroken smothering blanket. If there is no vertical surface, the discharge should be advanced in oscillating sweeps in the direction of the wind when possible, taking care to avoid foam plunging into the liquid. Foam spray streams, while limited in range, are also effective.
Flammable liquid fires of limited size can be rapidly extinguished with dry chemical
agents, but are subject to re-ignition when hot surfaces are in contact with flammable vapors. Combustible liquid fires which have not been burning for an extended period can be extinguished by water fog or water spray if the whole burning surface is accessible. The surface of the burning oil transfers its heat rapidly to water droplets which present a very large cooling surface area. The flame can be extinguished with advancing and oscillating sweeps of fog or spray across the complete width of the fire. Any oil fire which has been burning for some time is more difficult to extinguish with water, since the oil will have been heated to a progressively greater depth and cannot readily be cooled to a point where it
ceases to give off gas. Water should only be applied to oil fires as a spray or fog. The use of a water jet may spread the burning oil by splashing or overflow.
An aspect that must be borne in mind with liquid petroleum is the risk of re-ignition, so that a continuing watch and preparedness should be maintained.
1.2.3 CLASS C - ELECTRICAL EQUIPMENT FIRES
Class C fires involve energized electrical equipment. These fires may be caused by a short circuit, overheating of circuits or equipment, lightning, or fire spread from other areas. The immediate action should be to de-energize electrical equipment. Once deenergised, a non-conductive agent such as carbon dioxide should be used. Dry chemical is an effective non-conductive extinguishing agent, but is difficult to clean up after use. If the equipment cannot be de-energised, it is vital that a non-conductive agent be used.

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