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.

Adityanand Girdhari

There is a need to effectively develop and test an advanced fire detection system for aircraft cargo compartments that significantly reduces false alarms and improves alarm time response. Title 14 Code of Federal Regulations Part 25.858 requires that aircraft detection systems alarm within 1 minute of the start of a fire. Gas concentrations, temperature fluctuations, and particulate levels are three main parameters representative of a complete fire signature. Current aircraft detection systems depend solely on one parameter, particulate levels, for the detection of this wide fire signature. Improved fire detection capabilities can be achieved by combining multiple fire signatures or parameters in specific algorithms.

An advanced fire detection system combining an ionization smoke detector, thermocouple, smokemeter, and a carbon monoxide (CO)/carbon dioxide (CO2) gas probe was installed in a Boeing 707 forward cargo compartment. A broad spectrum of fire and nuisance sources were tested to produce a matrix of extreme detector levels from all four sensors. This matrix provided alarm threshold criteria that aided in the development of a multisensor algorithm based on fire signatures such as CO and CO2 gas concentrations, temperature, ionization chamber voltage, and percent light transmission per foot. Multiple algorithms were created to determine the most effective multisensor algorithm that responded the fastest to fires while providing nuisance immunity. A spatial distribution analysis was conducted by using a Computational Fluid Dynamic (CFD) model to specify the physical range of the multisensor detector subjected to the optimized algorithm.

A multisensor algorithm combining CO2 gas concentrations, percent light transmission per foot, and ionization chamber voltage parameters produced a 100% success rate for detection of fires within 1 minute while providing nuisance immunity to those signatures tested. Comparison of computational and experimental alarm time, smokemeter, and ionization chamber results demonstrated the effectiveness of the CFD and provided strong evidence that the CFD can be used as a virtual detector to simulate fires with an average alarm time uncertainty of 2.57 seconds. Spatial distribution analysis from the CFD determined the physical range of the single multisensor detector to be at least 910 cubic feet, the volume of the Boeing 707 forward cargo compartment.

John W. Reinhardt

A comprehensive fire test program was conducted on aircraft ducting materials in an effort to continue mitigating the threat of in-flight fires. Previous work at the Federal Aviation Administration (FAA) William J. Hughes Technical Center has indicated that the current FAA vertical Bunsen burner test requirement could not adequately discriminate between materials that performed poorly and materials that performed well under realistic fire scenarios. From this effort, an alternative radiant heat panel test method was developed. It was demonstrated that this method was effective in evaluating the in-flight fire resistance qualities of aircraft ducting.

William M. Cavage

TKS anti-icing fluid is being used in a variety of platforms to provided anti-/deicing capability for smaller commercial aircraft. The flammable liquid is comprised of 85 percent ethylene glycol, 10 percent water, and 5 percent isopropyl alcohol, and questions about its potential hazards have been raised. These hazards include, but are not limited to, the heating of small puddles of fluid that were either spilled or leaked, dripping of the fluid on hot surfaces, and the contact of the fluid mist with ignition sources. Simple tests were performed to allow for a more basic characterization of the TKS anti-icing fluid flammability. These tests were (1) an ASTM D 56-87 flash point test, (2) a hot-pan flammability test, (3) a hot-surface ignition test, and (4) a spray flammability test.

As expected, TKS anti-icing fluid is flammable under the correct conditions. The flash point was found to be approximately 150°F, but the fluid appears to have a very low energy release when reacting. The fluid will burn if heated in a pan to approximately 250°F and subjected to an ignition source, but burns relatively cool. When dripped onto a hot surface, the fluid does not react but will probably display relatively violent characteristics if heated in a confined space above 750°F (approximate autoignition temperature). The fluid will burn in a mist at ambient temperature and pressure when exposed to a flame, but will not sustain a reaction when the flaming ignition source is removed. Only sporadic ignitions (no fireball) confined to small areas were observed when the mist was ignited with a spark.