Walk-through survey report: styrene exposures during fiber reinforced wind blade manufacturing at LM Glasfiber, Grand Forks, North Dakota, report no. EPHB-306-19a.
An important area of NIOSH research involves measures for controlling occupational exposures to potential chemical and physical hazards. In the early 1980s, NIOSH researchers conducted an engineering control technology assessment of styrene exposures in the fiberglass reinforced plastic (FRP) boat manufacturing industry. The study focused mainly on ventilation systems and work practices used in the open molding production of large FRP boats and yachts. In 2004, NIOSH engineers from the Engineering and Physical Hazards Branch (EPHB) of the Division of Applied Research and Technology (DART) began a follow-up assessment to evaluate worker exposures from new processes that were not necessarily used during the previous NIOSH study. Several of the technologies include processes that use low styrene resins, non-atomizing spray equipment, pressure driven rollers, improved ventilation, and closed molding. In September of 2007, environmental health and safety representatives from LM Glasfiber contacted NIOSH engineers to request participation in the styrene study. LM Glasfiber is a major wind-blade manufacturer that uses styrene-based resins to manufacture large FRP blades for the rapidly growing utility scale wind energy industry. Due to the similarities in the styrene-based resins and their similarities in the process, NIOSH engineers agreed that workers in a wind-blade manufacturing plant might have similar potential for styrene exposures as workers in boat manufacturing. On October 19, 2007, NIOSH/EPHB conducted a walk-through survey at LM Glasfiber, in Grand Forks, North Dakota. The primary purpose of this walk-through was to learn more about the FRP wind-blade manufacturing industry and to assess the suitability of this facility for an in-depth survey. The main goals of the walk-through survey were to obtain preliminary information about styrene concentrations in the plant and to observe the engineering exposure-control measures during the wind-blade manufacturing process. LM Glasfiber manufactures wind-blades using a closed molding process known as vacuum-assisted resin-transfer molding (V ARTM). LM Glasfiber is a Danish-owned company that operates on a global basis with twelve locations worldwide. With US wind power growing at a rate of 25-30% per year, LM Glasfiber has plans to open up new facilities to help meet the demands for this form of renewable energy. At the time of the survey, the LM Glasfiber facility in North Dakota was operating four shifts to manufacture wind-blades 24 hours per day, 365 days per year. Approximately 600 of the plant's 940 employees work in areas where they may be potentially exposed to styrene vapor. The major chemical component of concern in terms of occupational exposures in the FRP process is styrene. Styrene is a fugitive emission that evaporates from resins, gel-coats, solvents, and surface coatings used in the manufacturing process. The polyester resins used at the LM Glasfiber plant contain between 36 and 42 percent styrene. Styrene is an essential reactive diluent for polyesters because it reduces the viscosity of the polyester mixture making it thinner and more capable of coating fiber reinforcements allowing the reactive sites on the molecules to interact. As an active diluent, styrene will react in the free-radical cross-linking reaction. Cross-linking is the attachment of two chains of polymer molecules by bridges composed of molecular, in this case styrene, and primary chemical bonds. Since styrene is consumed as part of this reaction, there is no need for removal of the diluents after the part is formed. However, if the process is not controlled properly, vapors from the application and curing process may pose an inhalation exposure hazard for workers near the process. Humans exposed to styrene for short periods of time through inhalation may exhibit irritation of the eyes and mucous membranes, and gastrointestinal effects. Styrene inhalation over longer periods of time may cause central nervous system effects including headache, fatigue, weakness, and depression. Exposure may also damage peripheral nerves and cause changes to the kidneys and blood. Several studies have shown that styrene exposures were linked to central and peripheral neurologic, optic, and irritant effects when occupational exposures to styrene vapors in air were greater than 50 parts per million (ppm). There is also evidence concerning the influence of occupational styrene exposure on sensory nerve conduction indicating that: (1) 5% to 10% reductions can occur after exposure at 100 ppm or more; (2) reduced peripheral nerve conduction velocity and sensory amplitude can occur after styrene exposure at 50 to 100 ppm; (3) slowed reaction time appears to begin after exposures as low as 50 ppm; and, (4) statistically significant loss of color discrimination (dyschromatopsia) may occur. Some other health effects of low-level styrene exposure include ototoxicity in workers and experimental animals. Styrene exposure can cause permanent and progressive damage to the auditory system in rats even after exposure has ceased. Styrene has been shown to be a potent ototoxicant by itself, and can have a synergistic effect when presented together with noise or ethanol.
National Institute for Occupational Safety and Health, Division of Applied Research and Technology, Engineering and Physical Hazards Branch, Mail Stop R-5, 4676 Columbia Parkway, Cincinnati, OH 45226-1998