SUMMARYThe molecular design of semi-inorganic polymers has produced polysilphenylene-siloxane and polyphosphazene elastomers having comparable fire safety to heat resistant engineering plastics. In flaming combustion a polyphosphazene rubber had a four times lower peak heat release rate than the polyurethane elastomer currently used in fire-blocked aircraft seat cushions. Figure 1. In 1987 the Federal Aviation Administration (FAA) imposed federal airworthiness regulation (FAR) 25.853c on the flammability of aircraft seat cushions to delay their involvement in cabin fires [4,5]. This test for flammability of seat cushions involves subjecting a fully constructed seat cushion (e.g. Figure 2) to an oil burner flame for 2 min (Figure 3) and recording the mass loss of the cushion and the burn length. The FAA requirements are that the burn length of the cushion should not exceed 43 cm ð17 inÞ and the mass loss should not exceed 10% of the original weight. Manufacturers responded to these regulations by wrapping the polyurethane seat cushion in a fire resistant barrier fabric [3,5] (Figure 2). Seat fire blocking allowed manufacturers to pass the 2 min FAA certification test but the polyurethane foam burns vigorously when the fire blocking layer has been consumed (Figure 1). More recently, combustion-modified polyurethane foam rubbers have been developed [6], some of which pass the FAA seat cushion flammability test without the need for a fire blocking layer [7,8]. These second-generation aircraft seat cushions
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 a fire (modified 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.
Burning of polymer matrix composites in postcrash aircraft fires generates a complex mixture of combustion products comprised of gases, organic vapors, and particulate matter including airborne carbon fibers. There is concern among the fire fighting, investigative, and mishap response communities that an unusual health hazard is posed by this combination of combustion products. This paper presents an overview of the nature and potential hazards of acute exposure to airborne carbon fibers from fire and explosion involving advanced composites materials. Data from fire tests and crash-site investigations suggest that a small fraction of the fibers released in fires are respirable and can be inhaled deep into the lung. Most of the carbon fibers produced in fires are 2-10 times larger than the critical fiber size associated with asbestos toxicity, and their concentration is well below OSHA recommended levels for chronic exposure. At issue however are the toxicological effects of adsorbed combustion products. Chemical extraction shows that a large number of toxic organic compounds are adsorbed on these fibers, several of which are known carcinogens and mutagens in animals. At the present time there is no conclusive evidence linking airborne fibers from burning composites to any unusual health hazard. However, no toxicological studies have been conducted to assess the long-term health effects from exposure to a single high dose of fibrous particulates and any synergistic interactions with the organic chemicals.
The chemistry and properties of polymers containing the “fire smart” moiety 1,1-dichloro-2,2-diphenylethene (DDE) are described. These polymers are typically derived from the bisphenol of chloral (bisphenol-C/BPC) and are low cost, easily processed, and have good mechanical properties and toughness under normal conditions. Under fire conditions, the DDE group undergoes an intramolecular rearrangement with the elimination of hydrogen chloride (a noncombustible gas) and intermolecular crosslinking to form an aromatic char residue in high yield. The flammability and mechanical properties of DDE-containing polymers are described.
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