Timothy R. Marker and Louise C. Speitel

This report summarizes the research effort undertaken by the Federal Aviation Administration to develop a laboratory-scale test method for evaluating the products of combustion inside an intact transport category fuselage during exposure to a simulated external fuel fire. An oil-fired burner, configured in accordance with Title 14 Code of Federal Regulations Part 25.856(b) Appendix F Part VII, was used to simulate the fuel fire, and a 4- by 4- by 4-foot steel cube box was used to mount representative test samples. The cube box simulated an intact fuselage and served as an enclosure to collect emitted gases during fire exposure. Test samples representing a variety of fuselage constructions were evaluated, including a noncontemporary prototype structural composite material (without thermal acoustic insulation). A typical cross section consists of a 40- by 40-inch aluminum panel representing the fuselage skin and the accompanying thermal acoustic insulation blanket behind the skin. Two thermal acoustical configurations were also tested. The first contained a heat-stabilized polyacrylonitrile fiber blanket. The second contained a ceramic paper barrier sandwiched under a fiberglass blanket. Each was encased by a thin metallized polyvinylfluoride moisture barrier. These burnthrough-resistant configurations were primarily run to provide a baseline for comparing the emitted gas concentrations with that of the prototype structural composite material.

A specialized Fourier Transform Infrared/total hydrocarbon gas analysis system was used to continually measure the products of combustion collected within the enclosure. Additional analyzers continuously measured the amount of carbon monoxide, carbon dioxide, and oxygen in the collected stream.

During the testing, it was determined that a prototype multi-ply structural composite material produced minimal quantities of toxic and flammable gases during a 5-minute fire exposure. Approximately 7 plies of the 13-ply composite material were delaminated by the fire exposure. By comparison, the aluminum skin/insulation configurations generated higher gas concentrations.

Subsequent full-scale testing of these material systems will provide gas scaling factors. The goal is to use this laboratory-scale test and scaling factors to predict decomposition products for an aircraft postcrash fuel fire.

Richard N. Walters and Richard E. Lyon

The flammability and mechanical properties of fiber-reinforced thermoset resin structural composites were evaluated. Processing characteristics, thermal stability, and flammability of the neat resins were measured using rheology, thermogravimetry, and pyrolysis-combustion flow calorimetry, respectively. Structural laminates were fabricated from liquid resins and woven glass fabric by vacuum-assisted resin transfer molding. Single-layer specimens (lamina) were prepared for fire testing using a hand lay-up technique. Mechanical properties of the laminates were measured in three-point bending. Fire behavior of the lamina and laminates was measured according to Title 14 Code of Federal Regulations 25.853(a-1) and Military Standard MIL-STD-2031. Results for flammability, fire performance, and mechanical properties of these composites are presented in this report.

Steven M. Summer

The Fuel Tank Flammability Assessment Method (FTFAM) is a Federal Aviation Administration-developed computer model designed as a comparative analysis tool to determine airplane fuel tank flammability as a requirement of Title 14 Code of Federal Regulations 25.981. The model uses Monte Carlo statistical methods to generate flammability data for certain unknown variables over known distributions for a large number of flights. The FTFAM iterates through each flight, calculating the flammability exposure time of each flight given the data input provided by the user. Calculating this flammability exposure time for a sufficiently large number of flights results in statistically reliable flammability exposure data. These calculations can be performed by the user for virtually any type of airplane fuel tank (body tank, wing tank, auxiliary tank, etc.) both with and without a flammability reduction method being employed.

This report serves as a user’s manual for this computer model to assist the user in its operation and to discuss the permissible changes that may be made to this model specific to a particular fleet of aircraft. It is updated through version 10 of the FTFAM. The user should reference Advisory Circular 25.981-2A for additional guidance on when to use this model and for a discussion of interpretation of results.

Stanislav I. Stoliarov and Richard E. Lyon

One main obstacle in developing more effective passive fire protection for transportation is the lack of a quantitative understanding of the relations between the results of various materials fire tests used in this field. The need for multiple testing techniques arises from the complexity of fire phenomena and their sensitivity to environmental conditions. This study addressed this problem by developing a computational tool that predicts the behavior of materials exposed to fire. While it is not expected that this tool will eliminate the need for fire testing, the goal is to considerably reduce the number and complexity of the tests necessary for a comprehensive characterization of the materials of interest. The foundation of this tool is a mathematical model that describes transient thermal energy transport, chemical reactions, and the transport of gases through the condensed phase. The model also captures important aspects of a material’s behavior such as charring and intumescence. This technical note provides a detailed description of the one-dimensional version of this model and summarizes the results of the model’s verification.

William M. Cavage and Steven Summer

The Fire Safety Team of the Airport and Aircraft Safety Research and Development Division performed tests at the Federal Aviation Administration (FAA) William J. Hughes Technical Center using the environmental chamber and the air induction facility (wind tunnel) to examine individual effects that contribute to commercial transport wing fuel tank flammability. Additionally, previously acquired wing tank flammability measurements taken during flight tests were compared with the results from the FAA Fuel Air Ratio Calculator in an effort to see if the calculations agreed with existing flight test data.

The results of the scale fuel tank testing in the environmental chamber showed that (1) fuel height in the tank had little or no effect on the flammability, (2) increasing the amount of heat on the top surface and a higher ambient temperature caused increased flammability, and (3) lower fuel flash point increased flammability greatly. Wind tunnel tests conducted with a section of a Boeing 727 wing tank showed that, under dynamic airflow conditions, change in ullage temperature was the primary mechanism affecting ullage flammability, not fuel temperature, as observed in environmental chamber tests. Other wind tunnel tests showed that the angle of attack of the fuel tank played little role in reducing fuel tank flammability, but that a cross-venting condition of the fuel tank would lead to a very rapid decrease in hydrocarbon concentration. An input temperature algorithm could be used with the FAA Fuel Air Ratio Calculator to significantly improve predictions of wing tank ullage flammability, based on tests that showed in-flight changes of ullage flammability in a wing tank are driven largely by the ullage temperature. This is very different from what had been shown with a center wing fuel tank, in which fuel temperature continues to be the main driver of flammability even during flight.