Robert Z. Filipczak

A new fire extinguisher concept, the adiabatic expansion nozzle, extends the usefulness of fire extinguishing compounds by lowering the temperature and discharge pressure of the agent. This allows total flood type halon replacements to be used in hand-held applications and, in the instance of carbon dioxide, produces a low-pressure dry ice snow.

Timothy Marker

A task group assembled under the auspices of the International Aircraft Materials Fire Test Working Group examined issues involving fire test approval of previously qualified interior material systems following renovation or alteration. A major problem associated with the alteration of interior system components is the difficulty in conducting certification tests that would determine if the altered interior component is still compliant with the heat release, smoke, and flammability certification requirements. In many instances, the appropriate substrates for conducting these follow-up certification tests are unavailable. As discussed in an earlier report, DOT/FAA/AR-TN95/83, International Aircraft Materials Fire Test Working Group, Material Systems Renovation and Repair Subgroup, the use of surrogate materials is the most feasible method for conducting certification tests following renovation, when samples of the actual buildup materials are unavailable. In order to validate the accuracy of using surrogate materials as heat release, smoke, and flammability predictors, tests were conducted in which several similar surrogate panels were compared. The surrogate panels were manufactured by three independent suppliers according to a common specification. Heat release and vertical Bunsen burner tests were conducted on the surrogate panels, which were finished with one of three paints or one of two laminates. The heat release test results indicate that each of the three surrogates reacts slightly different when tested without finish paint or laminate. When tested with a finished surface, the heat release results are even more scattered, providing evidence of the interrelationship between the substrate panels and the finish.

Richard Johnson and Lindsey Wuethrich

Child restraint seat used in aircraft are based on automotive designs that are required to pass a horizontal burn rate test method. The flammability of child seat materials was gauged against the Federal Aviation Administration (FAA) vertical Bunsen burner tests method. Basically, the vertical test prescribed in Federal Aviation Regulation (FAR) 25.853 (a)(1)(ii) allows a burn length of 8 inches and flame time of 15 seconds after exposure to a Bunsen burner flame for 12 seconds.

Eight child restraint seats were purchased from a retail store. The seats were disassembled in order to cut test specimens from the various seat components. Because of the size of the seat and use of materials, in most cases it was not possible to prepare the required sample size and replicates. However, this did not impact the overall conclusions regarding the flammability of the materials tested.

The test results indicated that the large majority of materials would not meet the FAA vertical fire test criteria. Also, some of the failed materials burned across the entire sample length, and others produced high flames or dense smoke. The findings are consistent with the knowledge that a horizontal burn test is far less severe than a vertical burn test.

Louise C. Speitel

The Federal Aviation Administration (FAA) has developed a unique extractive Fourier Transform Infrared (FTIR) system to analyze rapidly changing moist fire gas concentrations as a function of time. The system was designed to eliminate numerous errors generated by state-of-the-art FTIR systems for fire gas analysis. In addition, the path length, cell volume, sample flow rate, and system temperature were optimized to provide a rapid response and a sufficient dynamic range to detect gas concentrations generated in the cone calorimeter. A nonlinear classical least squares method was developed to analyze the FTIR data and generate the concentration histories and confidence limits of the 16 fire gases. Results of the technique are presented for flaming and nonflaming combustion tests of a mix of six common plastics.

Richard Walters and Richard E. Lyon

Specific heat release rate is the molecular-level fire response of a burning polymer. The Federal Aviation Administration (FAA) obtains the specific heat release rate of milligram samples by analyzing the oxygen consumed by complete combustion of the pyrolysis gases during a linear heating program. Dividing the specific heat release rate (W/g) by the rate of temperature rise (K/s) gives a material fire parameter with the units (J/g-K) and significance of a heat (release) capacity. The heat release capacity appears to be a true material property that is rooted in the chemical structure of the polymer and is calculable from additive molar group contributions. Hundreds of polymers of known chemical composition have been tested to date, providing over 40 different empirical molar group contributions to the heat release capacity. Measured and calculated heat release capacities for 80 polymers agree to within ±15%, suggesting a new capability for predicting flammability from polymer chemical structure.