Potential Health Hazards from Burning Aircraft Composites

Abstract

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.

Review of Smoke Toxicity of Fiber-Polymer Composites Used in Aircraft

“…Fibers inside the smoke plume occur in different forms, ranging from single filaments to fragments that can contain up to several hundred filaments bound together by char or resin. An analysis of graphite fibers collected in the smoke plume of burning graphite/epoxy composites has revealed that the mean fiber diameter is under 7 m, which is within the respiratory range [28]. Figure 4 shows a distribution plot giving the range of fiber diameters collected from the smoke of a graphite/epoxy laminate.…”

“…The toxic potency generally increases with the fiber concentration and when the fiber particle size is within a narrow range (usually in the micron size range). Several studies have measured the concentration and sizes of fiber particles in the smoke plume of burning composite materials, and the key findings have been reviewed by Gandhi et al [28]. The studies measured the amount and size of fibers released from burning graphite-epoxy composites [63][64][65][66][67][68].…”

“…4 Histogram showing the variation in fiber diameter before and after fire testing of a graphite/epoxy composite. Reproduced from Gandhi et al [28].…”

“…Furthermore, the review by Chaturvedi and Sanders was published in the mid-1990s and, since then, a great deal of new work has been published on smoke toxicity of aircraft composites. Other reviews into the smoke toxicity of composites have been published [28][29][30], although without considering the combined effects of the combustion gases, fiber fragments, and char particles.…”

Fire Tests for Composites

“…This is a desirable test for composite materials because the release of ultra-small fragments of the reinforcing fibres during combustion could be a health concern [34,35]. The soot yield can be determined by placing a filter sampler into the exhaust stream of the cone calorimeter.…”