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Aircraft Fire Extinguishing Systems

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Category: Fire Smoke and Fumes Fire Smoke and Fumes
Content source: SKYbrary About SKYbrary
Content control: EUROCONTROL EUROCONTROL

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Definition

Onboard systems designed to extinguish fires which occur either in the air or on the ground.

Description

Four types of fire extinguishing installations are found on commercial transport aircraft.

  • Portable Extinguishers installed at specified locations in both the main cabin and the flight deck
  • Hold fire extinguishing systems (with automatic detection)
  • Engine fire bottle extinguishing systems (with automatic detection)
  • Toilet waste bin bottle extinguishing systems

Portable Extinguishers

Fires on board aircraft which occur within the aircraft cabin or flight deck - or are potentially directly accessible from them - arise in one of three ways:

  • Fires in ordinary combustibles such as cloth, paper, rubber, and many plastics - in aircraft cabins typically in furnishings
  • Fires in flammable liquids, oils, greases, tars, oil-base paints, lacquers, and flammable gases - in aircraft cabins typically galley oven fires
  • Fires that involve energized electrical equipment - in aircraft cabins typically IFE (In Flight Entertainment) systems in the passenger cabin, electrical equipment in the galley or avionics equipment in the flight deck or under floor avionics bay

Portable extinguishers present a special challenge since they must be capable of extinguishing a range of fire types - solid materials such as cabin fixtures and furnishings, flammable liquids and electrical fires.

Halon 1211 extinguishers have entirely replaced the previous combination of two different types of portable extinguisher - Carbon Dioxide and Water Glycol - on new-build aircraft and no other single extinguisher-type has yet been identified as a satisfactory alternative to it. Where the dual fit of extinguisher is encountered on older aircraft, it is essential that Water Glycol extinguishers are used on solid material fires and Carbon Dioxide extinguishers on liquid or electrical equipment fires.

The minimum dispatch requirement for aircraft portable fire extinguishers is determined by the capacity of the aircraft cabin and is specified in the Aircraft MEL.

Hold Fire Extinguishing Systems

Hold fire extinguishing systems are usually activated as a flight crew response to abnormal heat detection in an aircraft hold, and usually operate in a dual function. Part of the available fire suppression capability is deployed in an ‘instant’, or ‘knock-down’, discharge of extinguishing agent and the remainder is deployed more gradually over a longer period of up to an hour, to assist in preventing re-ignition or at least providing partial fire suppression, to provide more time to get an aircraft with a continuing hold fire warning back on the ground. Various alternatives to Halon 1301 have been examined including water misting, inert gas and dry powder, either alone or in combination. The FAA has developed minimum performance standards for these systems and it has been demonstrated that although water misting alone is unable to pass the exploding aerosol can fire test, a combination of water misting and inert gas (nitrogen) discharge may be more effective. However, for such a solution to be viable, a means of on-board nitrogen generation will be needed.

Engine Fire Bottles

Fire Bottles in engine compartments are usually electrically operated after manual selection by the flight crew based upon automatic fire detection. In the airborne case, APU fire bottles are similarly activated but it is usual for automatic APU fire detection during ground operation to trigger automatic shutdown and fire extinguisher activation. The extinguishing agent universally remains Halon 1301 for all Engines/APUs fitted to civil transport aircraft. However, the US Air Force, Marine Corps and Navy have all developed alternative engine fire extinguisher systems which use HFC-125 and have been successfully tested and subsequently deployed in operational aircraft.

Toilet Waste Bins

Toilet waste bin fire extinguishers are activated automatically if heat detectors in the vicinity are activated. Toilet Smoke detector activation does not trigger waste bin fire extinguishers. Alternative extinguishing agents to Halon 1301 have been approved for use in fixed toilet waste bin systems and have also been, uniquely in terms of the search for Halon alternatives, shown to be more effective than Halon 1301 units whilst being the same size. Since only a documentation change is required to fit these alternative extinguishers, they have been used for retrofit as well as in new-build aircraft.

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