Fire and Smoke

By the inherent nature of the machine, fire is always a potential hazard where aeroplanes are concerned. The carriage of fuel which has a relatively low flash point, hot gases and hot materials and extensive use of and distribution of electricity, plus human interference, all make a volatile environment for fire to occur. Add to this ample supply of additional combustible material in the form of furniture, clothing and the contents of luggage and freight and a situation is created where, in any emergency situation, consideration of potential fire must be procedurally catered for.

In the design of the aeroplane, the manufacturer is required to build in fire detection and fire protection systems, detailing the correct use in the aeroplane manual (checklists). Likewise any maintenance schedule will contain procedures to reduce the possibility of fire during routine or non-scheduled maintenance. The operator is required to include procedures in the OM for abnormal and emergency operations whilst action specific checklists may either be verbatim extracts from the OM or extracts or annexes from the aircraft manual. In any case, such emergency drill action checklists are to be carried in the aeroplane.

The majority of situations to be catered for such as engine fires, fires in the cabin or the flight deck, hot brakes and the ingress of smoke and fumes into the aeroplane (this list is not exhaustive), require actions that are general in concept but modified by the individual type requirement.

A fire in the carburettor of a piston engine during engine start, caused either by malfunction of the engine (incorrect valve clearance or valve failure) or poor engine starting technique (‘pumping’ the throttle), requires a specific drill for the aeroplane (and engine) which will include the following actions depending on whether or not the engine has started. If it has not started, move the mixture control to ICO, open the throttle fully and continue to operate the starter motor. If it has started: keep it going. In either case, if the fire does not go out after a few seconds, action the engine fire drill (ground) specific for the aeroplane which will include: fuel off; electrics off; brakes off; evacuate the aeroplane.

In the case of an engine fire (other than above) other considerations must be taken into account in deciding the actions necessary. What is the situation of the aeroplane, airborne or on the ground? If on the ground, is the aircraft stationary or taxiing? If the aircraft is stationary, does it have passengers embarked, is it close to other aircraft (with or without passengers embarked) or near to a hangar or other vulnerable ground installation (refuelling point etc)? Clearly, the preservation of human life is paramount in any action, and consideration must be given to summoning trained specialist assistance (fire/rescue crews) and/or declaring the emergency to the relevant control unit. Again, type specific drills are required and these will be contained in or as an annex to, the aeroplane manual. However, initial actions in flight will be generally similar for the type of engine;

Piston Engines

Turn off the fuel (fuel selector off or mixture control to Idle Cut Off (ICO)) and allow the engine to run itself dry of fuel and stop. The engine and the induction system should then be purged of fuel and the fire should be extinguished. At this point the ignition should be switched off to the affected engine (making sure that the correct engine ignition system has been identified!)

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Fire in the Aeroplane

Engine fires are a rare event, and the extinguishant used to combat such fires is predetermined. However, the most likely scenario for a fire in an aeroplane is either a fire caused by electrical arcing or overheating of electronic equipment, or fire generated in the galley or careless/ deliberate extinguishing of smoking material where smoking is allowed. Illegal smoking is also a serious fire risk. In combating fire in the cabin and on the flight deck hand-held extinguishers are used. It is therefore necessary for cabin crew and flight deck crew to know which type of fire extinguisher should be used on what type of fire, and to be aware of the hazards associated with the use of extinguishers in the closed environment of the aeroplane.

The Number and Location of Hand-held Fire Extinguishers

The number and location of hand-held fire extinguishers should be such as to provide adequate availability for use, account being taken of the number and size of passenger compartments, the need to minimize the hazards of toxic gas concentrations and the locations of toilets, galleys etc. These considerations may result in the number being greater than the minimum specified.

Flight Deck Extinguisher

There should be at least one extinguisher, Halon 1211 (bromochlorodifluromethane, CBrCIF2) suitable for both flammable fluid and electrical equipment fires installed on the flight deck. Additional extinguishers may be required for the protection of other compartments accessible to the crew in flight.

Dry chemical fire extinguishers should not be used on the flight deck or in any compartment not separated from the flight deck, because of the adverse effect on vision during discharge and, if non-conductive, interference with electrical contacts by the chemical residues. Where a galley is not located on the main passenger deck, at least one extinguisher is to be provided at that location. Also, at least one readily accessible extinguisher is to be available in each class A or class B cargo or passenger compartment, and in each class E cargo compartment that is accessible to crew in flight.

The following table details the number of extinguishers which must be conveniently located in the passenger compartment:

Figure 11.1: Fire extinguishers

Where two or more extinguishers are required they must be evenly distributed in the passenger compartment. Where the maximum approved passenger seating is greater than 31 but less than 60, at least one extinguisher must be Halon 1211, and where the maximum approved passenger seating is greater than 61 two must be Halon 1211. Only Halon 1211 or water handheld extinguishers are cleared for use on aircraft. (Other extinguishants may be present in automatic systems)

The following classification of fires is now in general use and it is common practice to identify hand appliances in relation to the class of fire for which they are intended, such as ‘Class A’ extinguisher, etc. Where an agent may be used against more than one class of fire, such agents are generally referred to as general purpose agents.

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