A portable fire extinguisher by definition is an item of equipment for the purpose of extinguishing a fire. The reality is however that a portable fire extinguisher is effective only for the type and size of a fire that it is rated for.
Portable fire extinguishers are generally provided as "first attack" units in fire fighting and should be used only in early stages of fire
The six classes of fire are:
* Class A - Ordinary Combustibles
* Class B - Flammable and combustible liquids
* Class C - Flammable gases
* Class D - Combustible metals
* Class E - Electrically energized equipment
Wet Chemical extinguishers are typically installed in commercial kitchens for the protection from Class F fires where the fuel is cooking oils or fats. A wet chemical extinguisher is applied to a fire by forming a soapy foam blanket over the burning oil, smothering it and by cooling the oil below its ignition temperature.
The Chemical is expelled as a fine mist that does not cause grease to splash onto other surfaces. A Wet Chemical extinguisher may also be safely used in “A” class fires.
There are several types of dry chemical powder fire extinguisher, the two main types are, ABE Type - Effective on Class, A, B, C & E fires. BE Type - Effective on Class B, E & F fires. Note: Special powders are available to extinguish fires involving Class D combustible metals. Dry chemical powder fire extinguishers are effective because they interrupt the oxidation process. Dry-chemical powder is stored under pressure inside the extinguisher cylinder and is expelled when the hand-held trigger valve is depressed.
A water based extinguisher also referred to as a Stored Pressure Air-Water fire extinguisher is an extinguisher that is filled with water which is stored under pressure (normally by air). These extinguishers are only appropriate for use on Class A fires.
A water extinguisher is effective because it cools the fire, interrupting the exothermic reaction of a self-sustaining fire.
Carbon dioxide fire extinguishers are useful in protecting against fire when an inert, electrically non conductive, gas is desirable and where clean up from the agent must be minimal. Carbon dioxide extinguishers contain liquid CO2 that is expelled as a gas. Carbon dioxide blankets a fire, because of its heaviness, relative to air. It acts by preventing oxygen from getting to the fire, the result, the burning fuel deprived of the oxygen.
Carbon dioxide extinguishers are effective against Class “B” and “C” fires. Unlike other chemicals, CO2 does not leave a harmful residue and does not adversely affect the environment.