Full-scale test evaluation of aircraft fuel fire burnthrough resistance improvements

Fuselage burnthrough refers to the penetration of an external postcrash fuel fire into an aircraft cabin. The time to burnthrough is critical because in a majority of survivable aircraft accidents accompanied by fire, ignition of the cabin materials is caused by burnthrough from burning jet fuel external to the aircraft. There are typically three barriers that a fuel fire must penetrate in order to burnthrough to the cabin interior: aluminum skin, thermal acoustical insulation, and the interior sidewall/floor panel combination. The burnthrough resistance of aluminum skin is well known, lasting between 20 to 60 seconds, depending on the thickness. Thermal acoustical insulation, typically comprised of fiberglass bating encased in a polyvinyl fluoride (PVF) moisture barrier, can offer an additional 1 to 2 minutes if the material is not physically dislodged from the fuselage structure. Honeycomb sandwich panels used in the sidewall and floor areas of transport aircraft offer a substantial barrier to fire; however, full-scale testing has shown that a large fire can penetrate through other openings, such as the seams between sidewall panels, window reveals, and floor air return grilles. Of the three fire barriers, research has shown that large increases in burnthrough resistance can be gained by using alternate materials in place of the existing fiberglass based thermal acoustical insulation In particular, a heat-treated, oxidized polyacrylonitrile fiber was shown to increase the burnthrough resistance by several minutes over current insulation, offering potential life savings during a postcrash fire accident in which the fuselage remains intact.