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Thursday, April 29, 2010

Safety & Hazard in Composite Industry

Composite materials result from combining at least two different components to yield a new material whose properties differ from the original constituents. For example, concrete is a composite made of gravel and cement. The term took on a new meaning in the early 1960s when the aerospace industry began producing and testing structural components made of resins reinforced with carbon or boron fibers. With the successful use of these lightweight, high performance materials, new terms were coined: advanced composite materials (ACM) and high performance composites. Loosely defined, advanced composite materials are high performance man-made materials consisting of a fiber reinforced matrix system. ACM can be tailored for specific applications by combining resin and fiber properties to produce the desired weight, temperature resistance, and electrical conductivity or strength characteristics. The choice of resins is diverse - epoxy, polyimide, polyurethane, bismaleimide and metals, to name a few - as are the choices for fiber reinforcement - carbon, boron, aromatic polyamide, ceramic, glass and metal. Similarly, ACM applications are almost limitless, from aircraft components, satellite reentry shields and turbine engines to prosthetic devices, fishing rods and sports goods.

Along with the increasing usage of composite materials came the concern about possible associated health risks. Occupational health personnel were already familiar with the generation of vapors during chemical manufacturing processes such as those encountered during matrix production. The unknown parameters dealt with handling the raw fibrous materials and repairing composites. The heavy use of ACM in aircraft created another problem - what happens to the resins and the fibers during a fire or explosion? Concern escalated because fibrous materials were involved, and the inevitable possible parallel with asbestos fibers arose. The scientific community began searching for the answers to these questions.

However, the advanced composite industry is only about 30 years old - still in its infancy –so research data is limited. Epidemiological studies are almost nonexistent, and until recently, animal studies were conducted using artificial exposure routes. Thus far, the limited experimental evidence suggests potential problems when machining composites and during mishap scenarios involving ACM. This chapter summarizes the most current information on advanced composite materials, including chemical and physical properties of the components, exposure issues, regulatory standards and toxicological data. The intention is to provide information that will assist the industrial hygienist, occupational medicine physician and other medical department professionals in making informed decisions about the health hazards associated with ACM.

No attempt has been made to individually identify and discuss all composite components available. Such a document would be monumental; ACM technology, particularly matrix formulations, is still developing, improving and producing new variations. Consequently, matrices are discussed as broad categories, with specific constituents addressed as necessary to alert the reader to associated hazards. The reinforcing fibers are addressed specifically, since the potential for health risk from this component is still unclear.

It is important to understand the terminology in order to read and assess toxicological data. This section will concentrate on some of the basic terms and definitions that are applicable to the composite user, especially in reading Material Safety Data Sheets, the most common source of information on materials.