3 the water content of the foam provides a cooling

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3. The water content of the foam provides a cooling effect. The primary use of AFFF is to extinguish burning flammable or combustible liquid spill fires (class B). AFFF has excellent penetrating characteristics and is superior to water in extinguishing class A fires. Carbon Dioxide (CO 2 ) CO 2 is an inert gas and extinguishes fires by smothering them. CO 2 is about 1.5 times heavier than air, which makes it a suitable extinguishing agent because it tends to settle and blanket the fire. CO 2 is a dry, non-corrosive gas, which is inert when in contact with most substances and would not leave a residue and damage machinery or electrical equipment. CO 2 is a non-conductor of electricity regardless of voltage, and can be safely used in fighting fires that would present the hazard of electric shock. CO 2 extinguishes the fire by diluting and displacing its oxygen supply. If gaseous CO 2 is directed into a fire so that sufficient oxygen to support combustion is no longer available, the flames would die out. CO 2 has limited cooling capabilities, and may not cool the fuel below its ignition temperature. It is more likely than other extinguishing agents to allow reflash. CO 2 is however, not an effective extinguishing agent for fires in materials that produce their own oxygen supply, such as fires involving reactive metals like magnesium and titanium. Halon 1211 Halon is a halogenated hydrocarbon. Halon 1211, known chemically as bromo-chloro-difluoromethane, is colourless and has a sweet smell. Halon attacks the fire by inhibiting the chemical chain reaction. Halon decomposes upon contact with flames or hot surfaces above 900°F (482°C). Halon 1211 is used for twin agent (AFFF/Halon 1211) applications on board flight and with mobile fire-fighting equipment. (c) UPES, Not for Reproduction/ Sale
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UNIT 7: Aircraft Rescue and Fire Fighting Services Notes ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ ___________________ Potassium Bicarbonate (Purple-K-Powder or PKP) Potassium Bicarbonate (PKP) is a dry chemical principally used as a fire-fighting agent for flammable liquid fires. When PKP is applied to fire, the dry chemical extinguishes the flame by breaking the combustion chain. PKP does not have cooling capabilities on fire. PKP is highly effective in extinguishing flammable liquid (class B) fires. Although PKP can be used on electrical (class C) fires, it would leave a residue that may be hard to clean. Also, when combined with moisture, it may corrode or stain the surfaces it settles on. PKP does not produce a lasting inert atmosphere above the surface of a flammable liquid. Therefore, its use would not result in permanent extinguishing if ignition sources, such as hot metal surfaces or persistent electrical arcing, are present. Reflash of the fire will most likely occur. The ingredients used in PKP are non- toxic. However, the discharge of large quantities may cause temporary breathing difficulty and, immediately after the discharge, it may seriously interfere with visibility.
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