Timothy R. Marker, Louise C. Speitel

This report summarizes the Federal Aviation Administration research effort to develop a laboratory-scale test method for evaluating the thermal decomposition products produced 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 consisted of a 40- by 40-inch aluminum panel representing the fuselage skin and the accompanying thermal acoustic insulation blanket behind the skin. Two thermal acoustic 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 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 tests, 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 16-ply carbon/epoxy structural composite material were delaminated by the fire exposure. By comparison, the aluminum skin/insulation configurations generated higher gas concentrations.

Subsequent full-scale tests were conducted using these material systems inside a Boeing 707 fuselage. These tests were run to determine realistic levels of combustion products that can be generated inside the fuselage during a fuel fire when using burnthrough-compliant materials identical to those previously tested in the laboratory-scale tests. The full-scale tests used a fire-hardened steel cylinder test section in which insulation materials could be installed and evaluated against a standard 8- by 10-foot fuel pan fire. A comparison of the laboratory- and full-scale gas analysis results was made to determine the scaling factor for gas concentrations. By determining the scaling factors, an appropriate gas concentration acceptance level could be established for the laboratory-scale apparatus. The goal was to use this laboratory-scale test and scaling factors to predict thermal decomposition product concentrations for burnthrough-resistant insulation. The predicted full-scale concentrations can be used to assess the survival and health hazards of various insulation systems exposed to external fuel fires.

Constantine Sarkos

This technical note is an overview of Federal Aviation Administration (FAA) fire safety research over the past 10 or more years, with a focus on in-flight fire safety. The technical note emphasizes research accomplishments that have been, or are being, implemented into commercial aviation, as well as other important fire safety research. The research was driven by fatal accidents and safety concerns associated with new technology, such as:

1. Hidden fire protection research led to the development of an improved fire test method for thermal acoustic insulation, which became a new FAA requirement, and the issuance of airworthiness directives to remove certain flammable insulation.
2. A practical and cost-effective fuel tank inerting system was developed, enabling FAA to issue a regulation requiring flammability reduction in heated center wing fuel tanks. Related studies addressed the limiting oxygen concentration required to prevent a fuel tank explosion and fuel tank flammability.
3. A new test method was developed and mandated by the FAA that measures the burnthrough resistance of thermal acoustic insulation during a postcrash fuel fire.
4. Hazardous materials research led to the adoption of new regulations and advisory material to provide safeguards for the shipment of oxygen generators/cylinders, lithium batteries, and aerosol cans.
5. Research findings on structural composites were employed during the certification of the Boeing 787 to provide safety against a hidden in-flight fire, postcrash fire fuselage burnthrough resistance, and fuel tank flammability.
6. Minimum performance standards were developed for halon replacement agents in lavatories, hand-held extinguishers, engines and cargo compartments, and the effectiveness and safety of replacement agents was evaluated.
7. Long-range fire safety research identified promising new ultra-fire-resistant polymers and improved the science for experimental and theoretical evaluation of material fire performance.

In summary, FAA fire safety research over the past decade (2000-2010) developed technology that resulted in the adoption/issuance of five final regulations, two Airworthiness Directives, two Advisory Circulars, and two Safety Alerts for Operators, which are expected to significantly improve aircraft fire safety. In addition, this research also supported the certification of the all-composite fuselage, new Boeing 787 to ensure a high level of fire safety and the replacement of halon extinguishing agents and made important gains in characterizing and predicting the burning behavior of polymers and in developing ultra-fire-resistant interior materials.

Harry Webster

The Pipeline and Hazardous Material Safety Administration and the Federal Aviation Administration (FAA) are proposing a new regulation for the shipping of lithium-ion and lithium metal batteries and cells. Much of the regulation involves record keeping, package markings, cell size, and lithium content. Part of the regulation may restrict packaging, shipping mode, and cell type for shippers who elect to ship their devices on transport category aircraft.

The tests described in this report were designed to increase knowledge of the flammability of lithium-ion and lithium metal cells generated in earlier test efforts. Based on the previous work of the FAA William J. Hughes Technical Center Fire Safety Team, tests were conducted with larger number of cells and simulated self-ignition (thermal runaway) conditions. The effectiveness of Halon 1301 was evaluated from the perspective of open flame suppression as well as the ability to halt the propagation of thermal runaway within a shipment.

Preliminary tests were also conducted to characterize the flammability hazard of lithium polymer batteries that are used in some laptop computers.

The capability of existing shipping containers to contain lithium-ion and lithium metal cell fires was evaluated. A proposed performance standard for a shipping container or overpack for lithium-ion cells was developed.

Richard E. Lyon, Louise C. Speitel

A simple kinetic model for calculating the blood concentration history of humans exposed to time-varying concentrations of gaseous, halocarbon fire-extinguishing agents is described. The kinetic model was developed to extend experimental physiologically based pharmacokinetic (PBPK) models for arterial blood concentration of halocarbons, obtained from constant concentration exposure of dogs to time-varying exposure conditions for humans. In the present work, the simplified kinetic model was calibrated using published PBPK-derived arterial concentration histories for constant concentration exposure to several common fire-extinguishing agents. The calibrated kinetic model was then used to predict the blood concentration histories of humans exposed to time-varying concentrations of these fire-extinguishing agents in ventilated compartments and the results were compared with PBPK-derived data for the agents. It was found that the properly calibrated kinetic model predicts human arterial blood concentration histories for time-varying exposures as well as PBPK models. Consequently, the kinetic model represents an economical methodology for calculating safe human exposure limits for time-varying concentrations of gaseous halocarbon fire-extinguishing agents when only PBPK-derived human arterial blood concentration histories for constant exposure conditions are available.

William M. Cavage

Some concerns have been raised about the flammability characteristics of personal hand sanitizer, which is presently being used in lavatories on many commercial airlines to mitigate the spread of the H1N1 virus. Personal hand sanitizer is a fluid, which is generally composed of approximately 60% ethyl alcohol by volume, and comes in two primary forms: liquid and gel. To examine the general flammability characteristics of alcohol-based hand sanitizers, a series of small-scale tests were performed at the William J. Hughes Technical Center by the Fire Safety Team. Both gel and liquid hand sanitizers were examined. Tests were also performed to determine if hand sanitizer spillage could pose a significant fire threat. The effect of burning hand sanitizer on typical aircraft materials was examined. Antibacterial liquid soap was also burned adjacent to typical aircraft materials to compare with the hand sanitizer results.

As expected, hand sanitizer is flammable and can easily be ignited with a common grill lighter when poured into a pan. It tends to burn relatively cool, compared to fuel, plastic, or cellulose fires with peak flame temperatures between 500° and 1000°F. The observed temperatures above the flame were higher for the liquid hand sanitizer compared to the gel. The vapor is flammable and can be ignited by heating the liquid from the bottom and then igniting the vapor. The hot liquid does not have to be present to ignite the vapor; however, the vapor could not be ignited at room or elevated ambient temperatures (up to 100°F) without bottom-heating the hand sanitizer. When a nearly full bottle of sanitizer was involved in a fire started by burning paper towels, it burned hotter and somewhat vigorously. At one point, a fire burning adjacent to a 12-ounce liquid bottle of hand sanitizer reached temperatures in excess of 1500°F. When the hand sanitizer was burned adjacent to typical aircraft interior panels oriented horizontally or vertically, the panel did not ignite and burn independently, and there was no significant damage to the panel. From the tests conducted, burning hand sanitizer presents no significant risk to commercial transport aircraft fire safety, given the present cabin material flammability requirements.