Composites and fire
JF Mezei
fumes kill passengers and before you know it, there is no much left of
the aircaft.
Is there any knowledge on how differently composites react in a fire
compared to an aluminium structure ?
Aluminium doesn't generally burn at the lower temperatures in the
initial phases of a fire. However, when you look at the leftovers after
an aircraft fire, it is clear that it either burns or melts once the
fire really gets going. (The space shuttle's rocket boosters use
aluminium dust that does burn and increase thrust).
With aircraft now sporting more and more composites, how will composites
react in a fire ? Wouldn't the resin start to participate in the fire
quicker than aluminium ? While glass (used for fiberglass) may be fire
resistant, what about carbon fibres ? Wouldn't those act like charcoal ?
Also, wouldn't the resins generate more toxic fumes than aluminium ? Or
is this a case where the aircraft interiors generate so much toxic fumes
to begin with that adding the composite resin doesn't really make a
difference ? (like once you have enough nuclear bombs to destroy the
planet, it doesn't really make a difference if you add more).
If composites are more dangerous compared to aluminium in a fire, are
the manufacturers taking any steps to reduce the negative impact ?
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jbaloun
of fire burning through an aluminum vs. composite fuselage.
Quote
"If it takes about a minute for aluminum to burn through, it takes
composites substantially longer. "We've done tests on the order of 20
minutes," says Jeff Hawk, director-government, environment and
certification for Boeing's 787 program. By weight, 50% of the
Dreamliner is composite not just the empennage but wings, fuselage
skin, stringers and longerons.
Sarkos is convinced of the inherent fire-blocking properties of carbon
fiber. After all, the material is essentially pre-burned. His concern
is that while composite material may not burn through readily, "it may
outgas" and could build up toxic fumes inside the cabin. "There are
issues to be addressed," he believes. Hawk says, "We've specifically
been observing any fumes and smoke that's been emitted and we think we
will have no difficulty passing regulatory requirements."
End Quote
http://www.atwonline.com/magazine/article.html?articleID=1481
Another website explains how aluminum enhances combustion in the
environment of a solid rocket motor. A very different environment from
jet fuel on a fuselage.
http://www.aerospaceweb.org/question/propulsion/q0246.shtml
As for aircraft interiors, I have a little experience from 10 years ago
and I recall that there are definite requirements to use fire resistant
material with minimal smoke and fumes. I understand that the idea is to
delay the effects until the passengers can get out of the plane.
At my work we use dip-brazing to assemble aluminum parts. The salt bath
is around 1000F to 1100F degrees. The aluminum parts need to be
carefully supported because they are so hot they are soft. Only a few
hundred degrees from melting.
The comments in the article shed light on the flammability design
requirements of air transports and point at another of the factors that
led to the thinning of the 787 fuselage insulation. Thermal, sound and
flammability requirements led Boeing to thin the insulation and walls
and add an inch or two to the cabin while saving some weight.
James
jbaloun
of an emergency landing, all people should be on the main decks and not
in overhead rooms or bunks. Overhead sleepers are fine during cruise
but everyone will be in a seat during takeoff and landing. Any
occupancy in the overhead would have to allow for 90 sec evacuation.
Maybe two or four of the extra crew could be seated at the top of the
stairs in the overhead. An emergency escape hatch would be nice.
JF Mezei
>
> The article 'Staying Alive' in Air Transport World discusses the issue
> of fire burning through an aluminum vs. composite fuselage.
> Sarkos is convinced of the inherent fire-blocking properties of carbon
> fiber. After all, the material is essentially pre-burned.
Thanks for the link. However, I take issue with the above statement.
Composites don't contain just carbon fiber mat/cloth. They contain an
epoxy resin and/or some type of plastic compound to hold the fibers in
place.
Those resins will not only burn/melt, but also generate toxic gases. And
in terms of the carbon, the charcoal you buy for your barbequeue is also
"pre burned", but there is still a lot of burning potential left in it.
In a ceiling fire, I would also be concerned about large drops of
melted/hot resin on fire falling own and helping spread the fire. I
assume that insulation will help mitigate this issue.
To what extent are Boeing and Airbus' composite technologies (the
cloth/mat designs and the resins) secret/proprietary ? Or are they
commercially available products ?
Ken Rose
> Those resins will not only burn/melt,
Actually, a lot of the resins that are used in composites won't melt.
They'll decompose, and they'll burn, but the resulting substances are
either solids or gases. Often quite toxic gases, of course.
- ken