There has been a particularly concerted attack on the risk of fire in commercial aircraft since 1985. As usual it took serious accidents to concentrate the regulators' - and industry's - minds.
But despite the considerable advances in safety since then, through the use of more appropriate materials and improved cabin design, a new report has just shown the industry how far it has yet to go. It's a long, long way.
Since 55 people died of toxic fumes inhalation in a Boeing 737 on the runway at Manchester, UK, in 1985, there have been new rules governing the fire-resistance of cabin materials, and emergency exit size and design. Emergency cabin evacuation procedures have been influenced by considerable research on passenger and crew behaviour in emergency situations.
In May 1996, the ValuJet McDonnell Douglas DC-9 freight bay fire killed all 105passengers and five crew. This might have happened anyway despite improved freight bay fire protection because the illegal cargo which caused the fire generated its own oxygen supply (the culprit was illegally loaded chemical oxygen generators), but the rules governing freight bay fire suppression were nevertheless upgraded considerably. The primary cause of this accident, however, was the loading of illegal, unlabelled hazardous material in the first place.
Two months after ValuJet, the Trans World Airlines Boeing 747-100 fuel tank explosion killed 230 people. This was an explosion rather than a fire, but the ignition source is the key and it has not been determined. Since then there has been re-regulation on the routing of wiring near fuel tanks, on wiring bundle condition checks, improved wiring insulation materials, and fuel pump checks. Rules on nitrogen for fuel tank inerting are under consideration.
Then, in September 1998, 229 people died because of an inflight fire in a Swissair Boeing MD-11. Since then there have been more rules about wiring safety, and the metallised Mylar fuselage insulation has been replaced inMD-11s and other aircraft from the McDonnell Douglas stable. The final report has yet to emerge, but the Transportation Safety Board of Canada (TSBC) has issued a highly erudite interim report addressing the generic subject of fuselage fire risk in commercial aircraft.
Like many good reports it reveals things which are so obvious that they are ignored. For example, the simple fact that, in the case of cockpit and cabin fires which start behind panels, the only fire detector in most of the aircraft is the human nose - and eyes if the fire produces smoke.
In the report on the Varig Airlines Boeing 707 fatal accident on approach to Paris 27 years ago, the French Bureau Enqêtes-Accidents recommended that heat and smoke detectors should be more widely placed in fuselage areas.
In today's aircraft, electrical wiring is becoming not only more extensive - with in-flight entertainment equipment adding yet another layer to this proliferation of wiring looms - but progressively more vital to the aircraft's safe operation. It is accepted that all available wiring insulation materials have their weaknesses, and the job of choosing the most appropriate is a matter of risk assessment.
If a fire starts behind panels, any smoke and smell it emits may emerge some distance away from the point where the fire is burning. The TSBC report points out that efficient air conditioning systems can be fanning flames while delaying the detectability of the fumes by dissipating and filtering them.
All this means that the cabin crew, who have hand-held fire extinguishers available to them, might take a long time to locate the source of a fire and even then be unable to direct the extinguishant effectively because access is difficult or impossible.
It is not beyond today's industry to produce small, cheap, low-maintenance heat and smoke detectors to locate in the hidden spaces around cabins and cockpits. Perhaps infra-red detectors which could "see" hidden hot spots might be an answer. But the answer must be found.
Source: Flight International
