The very nature of aircraft makes them highly susceptible to fire. They carry large amounts of flammable fuel, as well as oxygen under high pressure

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1 Fire protection Fire protection begins with knowledge of the types of fires, what materials are involved, and which extinguishing materials will work best for each type Types of fires The very nature of aircraft makes them highly susceptible to fire. They carry large amounts of flammable fuel, as well as oxygen under high pressure The national fire protection association has classified fires into four basic types 1. Class "a" fires Combustible materials such as wood, cloth paper, upholstery materials Aircraft cabin fires or office area fires are usually of this type 2. Class "b" fires Combustible liquids such as gasoline, oil, grease, turbine fuel, and any of the paint thinners and solvents 3. Class "c" fires Energized electrical equipment is involved Special care must be exercised in the selection of a fire extinguisher 4. Class "d" fires Some metal, such as magnesium is burning The use of the improper type of extinguisher can intensify these fires, rather than extinguish them

2 Three requirements for a fire 1. Fuel Any material that will combine with oxygen and burn, and reduce itself to other chemical compounds Can be solid, liquid, or gas 2. Oxygen Does not actually burn, but supports combustion. No oxygen...no fire Combines chemically with another substance through the process of oxidation The concentration of oxygen determines the combustibility of the material A petroleum product, such as grease, will ignite at room temperature if it is blanketed with pure oxygen Even steel will actually burn when it is heated red-hot and a stream of pure oxygen is fed into it; this is the principle of oxyacetylene cutting 3. Heat The catalyst which accelerates the combining of oxygen with fuel Different fuels will have different kindling temperatures Gasoline, when raised to a relatively low temperature, will combine with oxygen and burn Remove any one of these "three requirements for a fire", and the fire will be out. This is the principal of fire extinguishment

3 Types of fire extinguishers In order to extinguish a fire, we must either lower the temperature of the burning material to below its kindling temperature, or deprive it of oxygen. All fire extinguishers in common use work on one of these principles Water extinguishers Can only be used on class "a" fires Aircraft cabin fires, office fires, waste paper basket, etc. (where electricity is not involved) Most water-type extinguishers consist of a container of water in which some antifreeze material has been mixed The water is propelled from the extinguisher by a charge of carbon dioxide (small CO 2 cartridge) Once the extinguisher is activated, all of the propellant will be discharged and a new cartridge must be installed when the extinguisher is serviced Carbon dioxide (CO 2 ) extinguishers Effective on both class "b" and "c" fires. Never use on class "d" fires- can cause an explosion Inert gas contained in a steel cylinder under a pressure of about 800 to 900 psi When released, it expands many times its compressed volume, its temperature drops, and it blankets the fire in the form of white snow The snow changes into CO 2 gas and pushes away all the oxygen; when there is no more oxygen for the fire, the fire goes out To use the CO 2 fire extinguisher, pull the safety pin and squeeze the handle assembly CO 2 is directed at the base of the fire from a horn attached to the valve CO 2 is heaver than air and is electrically non-conductive

4 Types of fire extinguishers (continued) Halogenated hydrocarbon extinguishers Most effective on class "b" and "c" fires, but can be used on class "a" and "d" fires, although somewhat less effective A halogen element is one of the group that contains chlorine, fluorine, bromine, or iodine When some of the hydrocarbons are combined with halogens, very effective fire extinguishing agents are produced Halogenated hydrocarbons are numbered according to chemical formulas with Halon numbers The most popular fire extinguishing agent for cabin fires in modern aircraft is Halon 1301 (also known as Freon 13) It is not harmful to humans in concentrations as high as 203 parts by volume Can extinguish a fire with a concentration of 2% by volume. This compares to about 40% by volume for CO 2 to extinguish the same fire Dry-powder extinguishers Effective on class "b", "c", and "d" fires. this is also the most effective type of extinguishing agent for metal fires, such as burning magnesium Dry powder is expelled from the container by compressed nitrogen and blankets the fire, excluding oxygen from the fuel Dry powder extinguishers are not recommended for aircraft because of the potential damage to electrical systems from the loose powder

5 Checking fire extinguishers All of the most commonly used portable extinguishers for the aircraft and aircraft maintenance shop have seals over the operating handle that tell at a glance whether or not the extinguisher has been discharged CO 2 extinguisher The content of the CO 2 is determined by its weight, with the weight of the empty container stamped on the filler valve Nitrogen pressurized dry powder Have pressure gauges on them, with red and green arcs on their dial Identifying fire extinguishers Fire extinguishers can be identified by color coded marks Indicates to the user the types of fires for which they are suitable A green triangle with a letter "a" is suitable for extinguishing class "a" fires (ordinary combustibles) A red square with the letter "b" identifies an extinguisher that is suitable for class "b" fires (flammable liquids) A blue circle with the letter "c" is for class "c" fires (electrical equipment) A yellow star with the letter "d" tell us that the extinguisher is suitable for class "d" fires (combustible metals)

6 Extinguishing a fire Used properly, a portable extinguisher can save lives and property by putting out a small fire or controlling it until the fire department arrives Portable extinguishers, in the shop, are not designed to fight large or spreading fires; they are useful only under certain conditions. The operator must know how to use the extinguisher as there is no real time to read the directions during an emergency The extinguisher must be within easy reach and in working order, fully charged Some models are unsuitable on certain types of fires Remember the pass-word Stand 6 to 8 feet away from the fire and follow the four-step pass procedure. If the fire does not begin to go out immediately, leave the area at once. Always be sure the fire department is called and also that they inspect the fire site. Pull the pin: this unlocks the operating lever and allows you to discharge the extinguisher. Some extinguishers have other devices that prevent inadvertent operation. Aim the nozzle: point the extinguisher nozzle (or hose) low, at the base of the fire. Squeeze the lever below the handle: this discharges the extinguishing agent. Releasing the lever will stop the discharge. Some extinguishers have a button that you press. Sweep from side to side: moving carefully toward the fire, keep the extinguisher aimed at the base of the fire and sweep back and forth until the flames appear out. Fight the fire upwind (wind blowing heat and smoke away from you). Watch the fire area. If the fire re-ignites, repeat the process.