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Category:Fire Smoke and also Fumes
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Definition

Halons are fire extinguishing agents which room gaseous once discharged in the plane environment. Halons have, until recently, been in nearly universal use in aircraft fire extinguishers, both portable and fixed. They exist in two creates - as Halon 1211, BromoChlorodiFluoromethane (CBrClF2) additionally known as "BCF", and as Halon 1301, Bromotrifluoromethane (CBrF3).

Halon 1211 is used only in portable extinguishers and is a streaming agentHalon 1301 is supplied only in resolved extinguisher installations commonly cargo holds or engines and is a full flooding agent.

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Description

Halons are electrically non-conducting and have been identified as the most efficient universal extinguishing certified dealer for aircraft use. Lock work largely by chemically interrupting the reaction defined as the "Fire Triangle" (Fuel-Oxygen-Heat) which should be sustained for a fire to continue. They execute not produce residues and therefore perform not cause secondary damage. However, the fumes space toxic if inhaled and all practicable precautions need to be taken when they space used.

The chemical constituents in Halon gases, and also the assets of the reactions they induce once discharged on fires, have actually been identified as causing damages to the Ozone layer. Together a result, their manufacture and use have been banned for numerous years in many countries and non-essential uses have been eliminated. However, the search for options of comparable effectiveness has actually proved an overwhelming and success limited, therefore they stay in vast use on plank aircraft for most applications.

How Halon Extinguishers Work

Both Halon variants work-related by a combination of chemical and also physical effects. The chemical effects, i m sorry are leading in their overall effect, are accomplished by the atoms in the gas directly inhibiting burning in two various ways:

Bromine, Iodine and Chlorine atoms act catalytically so the each atom participates repetitively in the scavenging of important free radicals from the combustion gases.Fluorine atoms reaction with complimentary radicals and form strong chemical bonds which neutralise combustion but can just do for this reason once and are then “consumed.” The physical results are both temperature reduction and also dilution.

Temperature palliation occurs, whenever a non-reactive gas is included to a flammable gas, because the warmth liberated by the reaction of oxygen molecules with a fuel resource must be spread into the overall environment. The rate of the combustive chemical reaction decreases promptly with to reduce in temperature and, if the concentration of included inert gas is high enough, the flame chemistry stops working altogether.

Halon gas mixtures are not just inert but of low temperature when released from your pressurised state. Dilution is a straightforward matter of reduce the collision frequency the the oxygen and also fuel resource so the there is a palliation in chemistry reaction rates. The size of this effect, however, is fairly small contrasted to chemistry inhibition and thermal effects, the former of these gift the primary one.

The toxicity that the Halon gases, especially the mix which renders up Halon 1211, is such that usage in confined spaces requires care to minimise any kind of inhalation of the discharged gases. Where a portable Halon extinguisher is supplied by cabin crew, it is commonly recommended to take into consideration donning a exhilaration hood before discharging the so as to eliminate this risk, but for pilot usage on the flight deck, this will not be an option and also risk awareness is the only defence.

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Alternatives to Halon

The search for Halon options for usage on plane has remained in progress because that at least 20 years and has actually only recently brought about potential success in the kind of the product marketed together "Halotron". Extinguishing agents in typical use generally are either formulations based upon sodium bicarbonate - perfect only because that fires involving flammable liquids and gases - or those known as ‘ABC’ which space usually based ~ above ammonium phosphate and are suitable for usage on fires of all origins. Both varieties may be supplied safely on fires where electrical circuits space present. However, back these species are the most reliable fire extinguishing agents in basic use, castle both leaving a an extremely fine, powdery residue ~ discharge which consists of particles the sub-micron diameter which is challenging if not impossible to clean up. This renders them unsuitable for usage on or in the vicinity of facility and often sensitive aircraft electrical systems. The ‘option’ of returning to the usage of the much less effective twin extinguisher-type equipment of Carbon Dioxide and also Water Glycol has actually not discovered favour either. Return Carbon Dioxide, together an extinguishing agent, is both ‘clean’ and also much cheaper 보다 both Halon or potential Halon replacements, its overall effectiveness per unit of stored volume is substantially worse than that of Halon. In addition, it can not be used on solid material fires and also the an approach of achieving effective discharge on other fires is also an ext complicated, request a pipe to horn shipment rather than nozzle discharge. Halon 1301, historically supplied in extinguishing solution on every Engines/APUs fitted to civil transport aircraft is no longer manufactured and has to be banned (for new systems) because 1994; regularly they are currently replaced by HFCs (Hydrofluorocompounds).