@newvisitor:
Thanks for your thoughtful post. I also have read with interest the posts from amicus, who is so obviously worried about the inflammibility of the epoxy resin in the composites make up the skin of the 787 fuselage, and who reports that he was on the losing side in a battle to get the upper part of the fuselage skin lined with thermal insulation.
I also read with interest from the FAA report on flammability properties of these materials that, "Typically, surface combustion needs a high temperature to be sustained, which is usually in excess of 500°C."
In isolation, that the material can burn is an interesting fact suggesting obvious concerns. But it seems to me that more must be taken into account in order to understand the implications of this fact for safety of air transport flights as dynamic systems.
I take as a premise that a powerful fire onboard a pressurized transport at altitude is an extremely dangerous event (whichever materials are used in the airframe), and generally non-survivable unless the fire's duration is limited by fire suppression or exhaustion of fuel/oxidizer.
Though I claim no expertise, I have worked as an engineer in the fire protection industry -- I wonder whether a fire capable of heating a significant area of composite cabin skin to 500+ Celsius for more than a few seconds wouldn't be quite a nasty blaze in its own right. I haven't done any of the analysis necessary to quantify this, which would have to take into account such factors as cooling by conduction to the outer surface.
Wondering about the safety issues of composite skins, brings several questions to mind:
1. Considering the kinds of fires that have been observed or are relatively likely in air transport cabins, how large and sustained would such fires need to be, in order to create the conditions required for sustained burning of the composite skin? For the purpose of discussion, I'll coin the name composite burn-up fires, or CBU fires for short, to refer to cabin fires sufficiently energetic to cause such skin burning.
2. How would conventional aluminium aircraft skins perform under the conditions of CBU fires as defined above?
3. Subtracting the combustion products from the composite skin itself, would the cabin air be able to sustain life in fires meeting the CBU criterion? What would the survivability implications be, regardless of airframe materials?
4. How much toxicity would combustion of the composite resins add to the cabin air, as compared to the toxicity from the CBU fire conditions that would precipitate skin burning?
I get that amicus objects strenuously to the 787's present application of these materials. My questions are about the practical safety implications of this technical vulnerability. In real-world fire scenarios (sadly, smoke/fire incidents on airliners are not so uncommon), what kind of differences in outcomes might be expected, taking the related factors into account?
In a way, we may be thankful for the incident in London, in which noone was hurt. Fire experts will be able to provide some estimates of the power and duration of the fire, offering a practical case of "how bad it got" in order to burn through the skin. Hopefully, the investigation will also address temperatures and toxicity of the cabin atmosphere during the blaze.
I also hope that some assessment can be made of the extent to which the aerostructures were compromised by the damage, and what the structural implications might have been for the plane's ability to land, had such damage occurred in flight.