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Fire detection is a topic of interest in aircraft applications, specifically cargo compartments, given the unique operating environment and accessibility challenges in the event of a fire. The use of unit loading devices inside cargo compartments have also presented a delay in alarm challenge due to their enclosed nature. However, despite the importance of detection, there is yet to exist a standard testing and certification method for fire detection in cargo compartments. The current requirement for a cargo compartment detection system is that a fire has to be detected in 1 minute, and in that time be so small that the fire is not a significant hazard to the airplane. Nuisance alarms also plague the industry, with upwards of 90% of fire alarms being false warnings. These problems have been partially addressed through the analysis of smoke density and state of the art detection technology. Both flaming and smoldering fires were conducted using an array of materials such as heptane, polyurethane foam, shredded paper, wood chips, suitcase, baled cotton, and boiling water. The response of aspirating smoke detectors, dual wavelength technology, and gas detectors were analyzed. It was found that smoke density scales with volume, leading to the suggestion that detection testing could happen outside of cargo compartments and results be appropriately scaled. The response of aspirating smoke detectors, dual wavelength technology, and gas detectors were all found to follow patterns similar to that of light obscuration measurements and were thus deemed viable options for use in cargo compartments. Carbon dioxide and the loss of oxygen were detected 100-600 seconds faster than visible smoke for smoldering polyurethane and smoldering cotton tests, suggesting an increase in gas concentration could be a precursor to visible smoke.
The FAA has published two previous versions of the Aircraft Materials Fire Test Handbook: DOT/FAA/CT-89/15 and DOT/FAA/AR-00/12. The main purpose of the Handbook is to describe various fire test methods for aircraft materials in a consistent and detailed format. The Handbook provides information to enable the user to assemble and properly use certain test methods. The FAA adopted policy that made the first two versions of the Handbook an acceptable method of compliance for certain requirements in 14 Code of Federal Regulations (CFR) Part 25. This third-generation Handbook supports an FAA effort to revise the flammability requirements for Transport Category Airplanes in 14 CFR Part 25.
This Handbook organizes the test methods according to the threat posed by the material and its function. It describes various types of flammability tests in a consistent and detailed manner, and provides information to help the user assemble, operate, and use the test methods. Appendices contain additional information to broaden the utility of the Handbook.
The fire behavior of heat-resistant polymers was measured to set a benchmark for the properties of polymers used in aircraft interiors and compare them with specialty and developmental polymers. Fire (cone) calorimeter tests were conducted on polyetherimide, polyamideimide, polyethylenenaphthalate, polysulfone, bisphenol-A polycarbonate, polyphenylenesulfide, polyetheretherketone, polyetherketoneketone, polyimide, polyphenylsulfone, and the polycarbonate of 1,1-dichloro-2,2-bis(4-hydroxyphenyl) ethylene (bisphenol-C). Fire calorimetry data were collected for the time to ignition, mass loss rate, heat release rate (HRR), and yields of flaming combustion products. Fire parameters derived from these data include critical radiant heat flux for piloted ignition, thermal inertia, heat of gasification, and ignition temperature. These thermoplastic polymers generated significant amounts of char when burned and exhibited relatively low HRRs as a consequence of the low volatile fuel fraction. The critical heat flux for ignition (fire resistance) of these thermoplastic polymers is a condensed phase criterion for ignition that increases with thermal stability because radiation and convection losses at the heated surface increase with polymer thermal decomposition temperature. However, the mass and energy flux at ignition are independent of thermal stability because these are gas phase criteria for the onset of flaming combustion. When ignited, the HRR of these heat-resistant polymers increases with the fuel value of the pyrolysis gases and the mass fraction of char, which protects the underlying polymer by reradiating incident energy and insulating the surface.
Hidden fire in the aircraft cabin has been characterized as a hazardous phenomenon to in-flight safety and could lead to catastrophic disaster. Detecting hidden fire at the earliest stage is required and can be achieved only through an improved understanding of the transport of hot gases and smoke due to a possible hidden fire. This research uses the computation fluid dynamics tool to simulate the heat and mass transport in situations of hidden fire in the overhead area of the aircraft cabin. The modeled temperatures are compared with the full-scale test results, and reasonable agreements are observed. The simulation also presents comprehensive hot gas transport information. Further investigations are performed to examine the effect of ambient pressure and the fire source location. It is found that at cruise altitude with reduced ambient pressure, ceiling temperature increases as a result of increased flame height and decreased air entrainment. The ceiling temperature is sensitive to the fire source location. Hot gases tend to migrate to the highest ceiling location. Obstruction thicker than the ceiling jet boundary layer at the ceiling level can result in extra hot spots.
The Next Generation (NexGen) (sonic) burner is a new burner designed by the FAA William J. Hughes Technical Center for the required FAA fire certification tests on power plant components. The objective of this study is to understand the performance of this burner and provide the benchmark to adapt the burner settings for future FAA fire tests. Tests have been conducted to study the burner performance and its sensitivity to operating conditions and changes in configuration. Tests were conducted on the old burner configuration consisting of the stator and turbulator, and the updated configuration consisting of the flame retention head and the static plate. Burner calibration was found to be sensitive to changes in fuel flow rate, but not to air mass flow rate, though burnthrough results were sensitive to both parameters. Results were not affected by fuel and air temperatures as long as the air mass flow rate was held constant at the different air temperatures. Changes in burner inclination were observed to affect the burner performance. For the updated burner configuration, tests were conducted to study the effect of changes in the internal configuration. The NexGen burner performance was observed to be robust, and tolerances have been specified for some of the internal configuration components.
This report discusses ongoing developmental efforts related to the NexGen burner. It should be noted that the burner construction and settings discussed in this report are not representative of the most recent ones used on the NexGen burner. For detailed construction drawings and to view other documentation and presentations that discuss the most up-to-date burner configurations, please visit the FAA’s Fire Safety Branch’s website at www.fire.tc.faa.gov.