Aircraft Fire Extinguishing Systems

Aircraft Fire Extinguishing Systems

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Definition

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

For information on detecting and fighting fires in the cabin, see also the separate article: "Passenger Cabin Fire"

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.
  • Cargo hold fire extinguishing systems (with automatic detection).
  • Engine fire bottle extinguishing systems (with automatic detection).
  • Toilet waste bin bottle extinguishing systems.

Portable Extinguishers

General

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 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 underfloor avionics bay, or personal electronic devices (PEDs) carried by passengers.
  • 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.

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 gycol - on new-build aircraft, and no other single extinguisher type has yet been identified as a satisfactory alternative to it.

NOTE: Crews must be aware that the toxicity of the Halon gases, especially the combination which makes up Halon 1211, is such that use in confined spaces requires care to minimize inhalation of the discharged gases. Where a portable Halon extinguisher is used by cabin crew, it is usually recommended to don a smoke hood before discharge to eliminate this risk, but for flight crew use on the flight deck, this will not be an option and risk awareness is the only defence.

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.

Regulatory Requirement

Relevant authorities (e.g. the European Union Aviation Safety Agency (EASA) in the EU, FAA in the US) specify the requirements for hand held fire extinguishers in terms of:

  • Minimum number of handheld fire extinguishers to be carried on board. This depends on the size of the aircraft, the number of passenger seats, the number and type of cargo compartments, etc.
  • Handheld fire extinguisher distribution within the aircraft (e.g. number of extinguishers in the cockpit, cabin, cargo compartments, etc.).
  • Mounting and marking (e.g. there should be a special sign in case the fire extinguisher is not clearly visible).
  • The need for regulatory approval and acceptable means of compliance.
  • Restrictions regarding the extinguishing agents used (e.g. cutoff and end dates for Halon-based extinguishers).
  • Extinguishing agent quantity requirements (e.g. minimum amount of agent per extinguisher).
  • Health considerations (e.g. toxic gas hazard minimization).

Hold Fire Extinguishing Systems

Cargo 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. The remainder is deployed more gradually over a longer period of up to an hour, to assist in preventing reignition or at least providing partial fire suppression, to provide more time to get an aircraft 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. Until recently, the most common extinguishing agent was Halon 1301 for all Engines/APUs fitted to civil transport aircraft. However, Halon 1301 is no longer manufactured and has been banned (for new systems) since 1994; often they are now replaced by HFCs (Hydrofluorocompounds).

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.

Personal Electronic Devices

Equipment has been introduced, designed to deal specifically with lithium battery fires in PEDs; lithium ion batteries (Li-ion) are used to power PEDs such as cellular phones, portable tablets, EFBs and digital cameras; Li-ion batteries are rechargeable. Non-rechargeable lithium batteries (Li-metal) are similar to Li-ion, but use a different electrode material – metallic lithium.

All lithium batteries present a potential fire hazard. These batteries are carried on aeroplanes as cargo, in passenger baggage, and by passengers directly. Like some other batteries, lithium batteries are capable of delivering sufficient energy to start an in-flight fire. Lithium batteries present a greater risk of an in-flight fire than some other battery types because they are unable to contain their own energy in the event of a catastrophic failure.

Once extinguished, a lithium battery fire – or a fire in a PED powered by lithium batteries – requires containment and continued cooling. Halon 1211 or water fire extinguishers are effective at extinguishing the fire and preventing its spread to additional flammable materials. After extinguishing the fire, dousing the electronic device with water or other non-alcoholic liquids cools the device and prevents additional battery cells from reaching thermal runaway. Containment devices are now available and where these are equipped, crews should receive specific training in how to use them to greatest effect.

These issues are discussed in some detail in the RAeS document "Smoke, fire and fumes in transport aircraft, past history, current risks and recommended mitigations - Part 1:References". See also the separate articles: "Aircraft Fire Risk from Battery-powered Items Carried on Aircraft" and 'Personal Electronic Device Fire - Cabin Crew Checklist".

Accidents and Incidents

Hand held extinguisher used

B772, en-route, near Marseille France, 2023

On 9 February 2023, a Boeing 777-200ER was en-route near Marseille when the cabin crew observed smoke coming from a rear galley oven which was spreading into the rear passenger cabin. After an immediate initial response and use of multiple Halon Fire extinguishers, the smoke ceased after about 20 minutes but the fumes remained. Although this meant no ongoing emergency existed, some cabin crew and passengers had experienced breathing difficulties and it was decided to return to Amsterdam. The cabin crew response to the situation was subsequently assessed as contrary to applicable procedures and relevant cabin crew training seemingly inadequate.

B789, en-route, west of Swansea UK, 2020

On 1 October 2020, a Boeing 787-9 was approaching the top of descent when the cabin crew discovered a mobile phone crushed in a flat bed seat which had just been changed to the seated position for landing. A fire which had started was extinguished and the Captain declared a ‘PAN’ to ensure the fire service attended the arrival. The Investigation noted that there are currently no seat design requirements to prevent electronic devices from becoming trapped in seats and that it is proving challenging to find a workable solution. A Safety Recommendation to improve seat design regulations was made.

B744, Phoenix USA, 2009

On 10 January 2009, a Boeing 747-400 being operated by British Airways on a scheduled passenger flight from Phoenix USA to London had been pushed back from the gate in normal daylight visibility and the engines start was continuing when fumes and smoke were observed in the cabin and flight deck. The aircraft commander decided to return to the stand but there was some delay while the tug was reconnected and the movement accomplished. The intensity of the fumes increased and as the aircraft came to a halt on the stand an emergency evacuation was ordered.

A320, vicinity New York JFK NY USA, 2007

On 10 February 2007, smoke was observed coming from an overhead locker on an Airbus A320 which had just departed from New York JFK. It was successfully dealt by cabin crew fire extinguisher use whilst an emergency was declared and a precautionary air turn back made with the aircraft back on the ground six minutes later. The subsequent investigation attributed the fire to a short circuit of unexplained origin in one of a number of spare lithium batteries contained in a passenger's camera case, some packaged an some loose which had led to three of then sustaining fire damage.

B738, en-route, Colorado Springs CO USA, 2006

B738 diversion into KCOS following in-flight fire. The fire started after a passenger's air purifier device caught fire whilst in use during the flight. The user received minor burns and the aircraft cabin sustained minor damage.

DC93, en-route, Cincinnati OH USA, 1983

On 2 June 1983, a DC9 aircraft operated by Air Canada was destroyed following an in-flight fire which began in one of the aircraft s toilets. 23 passengers died in the accident.

Related Articles

Further Reading

RAeS and Air Pilots The Royal Aeronautical Society and Honorable Company of Air Pilots jointly revised and reissued valuable reference documents on this topic, which should be used as first references for flight crew on this topic:

FAA

Airbus

Categories
Fire Smoke and Fumes, Fire Protection

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