Richard E. Lyon, Louise Speitel, Robert Filipczak, Richard Walters, Sean Crowley, Stanislav Stoliarov, Lauren Castelli, and Michael Ramirez

The chemistry and properties of polymers containing the fire-smart moiety 1,1-dichloro-2,2-diphenylethene (DDE) are described. These polymers are typically derived from the bisphenol of chloral and are low-cost, easily processed, and have good mechanical properties and toughness under normal conditions. Under fire conditions, the DDE group undergoes an intramolecular rearrangement to diphenylethynyl with the elimination of hydrogen chloride (a noncombustible gas) and intermolecular cross-linking to form an aromatic char residue in high yield. The flammability and mechanical properties of DDE-containing polymers are described.

Patricia Cahill, Timothy Marker, & John Reinhardt

Intermediate-scale flammability testing of Hypalon™ RB71, a thermal acoustical insulation primarily used to insulate ducts, was conducted in a section of a wide-body aircraft. The aircraft section was configured to represent the attic area of a transport category aircraft. Baseline tests were also conducted using metallized Tedlar™ film cover over fiberglass to wrap the ducts. Temperature versus time and the relative energy release rate versus time were evaluated and are presented in this report.

Paul M. Hergenrother, Craig M. Thompson, Joseph G. Smith Jr., John W. Connell, Jeffrey A. Hinkley, Richard E. Lyon, and Richard Moulton

As part of a program to develop fire-resistant exterior composite structures for future subsonic commercial and general aviation aircraft, flame-retardant epoxy resins are under investigation. Epoxies and their curing agents (aromatic diamines) containing phosphorus were synthesized and used to prepare epoxy formulations. Phosphorus was incorporated within the backbone of the epoxy resin and not used as an additive. The resulting cured neat epoxy formulations were characterized by thermogravimetric analysis, propane torch test, elemental analysis, microscale combustion calorimetry, and fire calorimetry. Several formulations showed excellent flame retardation with phosphorous contents as low as 1.5% by weight. The fracture toughness and compressive strength of several cured formulations showed no detrimental effect due to phosphorus content. The chemistry and properties of these new epoxy formulations are discussed.

Stanislav I. Stoliarov, Qaadir Williams, Richard N. Walters, Sean Crowley, and Richard E. Lyon

The widespread use of brominated flame retardants and fire extinguishing agents in aircraft cabins and recent concerns about their combustion toxicity and environmental impact prompted a study to understand the mechanism by which bromine inhibits the flaming combustion of plastics as a first step towards identifying alternative chemicals or compounds. The heats of combustion of bromine-containing epoxies were calculated from the known atomic composition and compared to measured values in flaming and nonflaming combustion. The heat of flaming combustion was measured in a fire/cone calorimeter (CC) and by burning pyrolysis products in a methane laminar diffusion flame (pyrolysis-flaming combustion calorimetry (PFCC)). Heats of nonflaming combustion were measured by pyrolysis-combustion flow calorimetry (PCFC). The results of these tests indicate that the combustion heat released by these materials decreases with increasing amounts of brominated components as a result of incomplete combustion, char formation, and dilution of the materials with noncombustible bromine. Gas-phase combustion efficiency in the various test methods decreased as: PCFC > PFCC > CC.

Robert I. Ochs

This technical note describes research performed to determine the ignition hazard presented by small fragments of superfine steel wool that contact energized direct current wires in aircraft fuel tanks. Several different methods of shorting a circuit with steel wool were explored. An ignitable mixture of hydrogen, oxygen, and argon, calibrated to have a minimum ignition energy of 200 micro Joules, was used as an ignition detection technique. The electrical currents at the ignition threshold were recorded to determine safe maximum allowable current limits for fuel tank electronics. The lowest current found to ignite the flammable mixture was 99 milliamps (mA); the lowest current found to ignite a steel wool wad in air only was 45 mA.