James G. Quintiere, Richard N. Walters, and Sean Crowley

This study investigated the flammability of a carbon-fiber composite material for use in aircraft structures. In particular, it considered a composite material manufactured by Toray Composites (America) to Boeing Material Specification 8-276. The objective was to establish a complete set of properties pertaining to the heating and burning characteristics of these materials in fires. Several apparatuses were used, including the cone calorimeter, microscale combustion calorimeter, thermogravimetric analyzer, differential scanning calorimeter, and a flame spread rig to promote spread with preheating by radiation. An attempt was made to measure the thermal conductivity of the composite over a range of temperatures through its decomposition, but the heat losses from the apparatus likely caused an overestimate in the measurement. Data from standard tests were also reported for the Ohio State University calorimeter and the smoke density chamber.

The material burns in a manner similar to a charring material, in that the carbon fibers comprise most of its mass. The composite burns primarily from the vaporization of its resin. It can ignite with a pilot flame after preheating at a low heat flux. When it burns, the resin vapor is forced out of the fiber pores, and pressure causes the material to swell to over twice its volume. In most all cases studied, the composite maintained its rigidity, but its structural strength was not examined after degradation. The material appears to maintain homogeneity in swelling. The fibers create an insulating, char-like structure that causes a reduction in the internal heating, and consequently, the burning rate drops in time. As the burning rate drops, extinction can naturally occur due to insufficient heating. As is common of charring materials, external heat flux is required to sustain burning and flame spread. It should be noted that the carbon fiber can also oxidize under high-temperature conditions, and this was observed even at low heat fluxes. Furthermore, the properties in this report pertain primarily to the characteristics of the resin material, as the carbon fibers are essentially inert.

The data in this report can be used for modeling and explaining the fire behavior of the composite in fire scenarios associated with aircraft operations.

Timothy R. Marker

Twenty hand-held extinguisher tests were performed in the overhead space in both narrow- and wide-body aircraft. These tests simulated a typical hidden fire in the inaccessible area above the cabin ceiling by using a number of small, controllable candle lanterns. The purpose of the tests was to determine the performance of the Federal Aviation Administration-required, hand-held Halon 1211 extinguishers against a fire in this area when discharging the agent through a ceiling-mounted port. In an effort to maximize agent performance, the port design was modified as these tests progressed. The tests indicated that individual hand-held extinguishers did not predictably extinguish fires in the large-volume cabin overhead area typical of a wide-body aircraft, regardless of the port design. However, the use of ceiling-mounted discharge ports combined with hand-held extinguishers was more promising against fires in the more confined and smaller-volume overhead area typical of a narrow-body aircraft. Additional work would have to be performed to further develop and optimize this concept.

Jill Suo-Anttila, Walt Gill , Anay Luketa-Hanlin, and Carlos Gallegos

A computational model designed to predict smoke and gas transport within aircraft cargo compartments has been validated for potential use in the certification process of cargo compartment fire detection systems. The simulations and experiments compared herein represent a spectrum of scenarios that provide confidence in the models’ ability to predict the transport of smoke and combustion products in a variety of conditions. The main variables that changed between the cases were fire location, compartment size, and ventilation. Validation metrics suitable for fire detection system response were selected and, overall, the model favorably predicted these metrics for the selected cases. The model can now be used with improved confidence to simulate certification scenarios of interest to assist in designing the optimum detection systems for cargo compartments.

Xin Liu and J.G. Quintiere

The flammability properties of nylon samples with different percentages of clay dispersed on the nanometer (molecular) scale were measured by a fire (cone) calorimeter. Specifically, chemical energy release rate, mass loss rate, and time to ignite (melt and char) were measured. This study consisted of samples of pure Nylon 6 and nylon that contained nanoclay additives at 2% and 5% by weight. In addition, the effect of sample thickness was considered for 1.6 to 24 mm. Data obtained over a range of radiant heat flux (17 to 55 kW/m2) were analyzed to illustrate the effect of sample clay loading and thickness on heat of combustion, heat of gasification, and ignition temperature. The findings indicated that the heats of combustion based on mass loss did not change with clay loading, and were 28 ±1 kJ/g. The critical heat flux for ignition did not appear to be influenced by the clay additive; it decreased from 17.7 for pure nylon to 16.0 with 5% clay addition. These values correspond roughly to an ignition temperature of 430° C, compared to a decomposition temperature range from a thermogravimetric analyzer of 350° to 430°C. However, the addition of the clay could increase the ignition time by 30% to 100% over the pure nylon. This is believed to be due to the increased char residue and the decrease in the mass loss rate. The char-like residue yield was nearly identical to the clay loadings. The overall average mass loss rate was reduced by up to 50% with a 5% clay composition over pure nylon for a given heat flux and thickness. For the clay nanocomposites, the burning rate increased as the thickness decreased.

Joshua L. Jurs

Novel flame-retardant chemical additives and polymers were synthesized and their flammability measured in the Underwriters Laboratory test for flammability of plastics (UL94). Self-extinguishing (V-0) compositions were obtained for poly (acrylonitrile-butadiene-styrene) and high-impact polystyrene by adding as little as 10 weight percent of boronic acid derivatives or halogen-containing bisphenylethenes (BPH). Self-extinguishing (V-2) compositions were obtained for polyethylene by adding as little as 10 weight percent BPH. The efficacy of BPH additives as flame-retardants suggested incorporating these moieties directly into the polymer to further reduce flammability. Polymers and copolymers were synthesized having BPH backbone and pendant groups, including backbone copolymers containing acetylene and phosphineoxide. The thermal combustion properties of polymers containing a BPH backbone or pendant groups were measured by microscale combustion calorimetry and found to be among the lowest values ever recorded, suggesting that aircraft cabin materials made from these polymers would be ultra-fire-resistant.