The occupational scene of styrene

Styrene readily undergoes homopolymerization as well as copolymerization with other monomers, such as acrylonitrile and butadiene. In closed polymerization processes, exposure of workers to styrene is generally lower than current reference values (20-50 ppm), but high peaks of exposure may occur during the cleaning, filling and maintenance of reaction vessels and during transport of liquid styrene. Styrene is used not only in styrene polymers but also as a reactive solvent in the manufacture of unsaturated polyester resins. During the lamination process, when resins are applied manually or by spraying in open moulds, workers are exposed to styrene at concentrations that are on average two or three times higher than the 8-h time-weighted average hygienic standard, 20 ppm. Further, exposures during the open mould process tend to fluctuate widely, so that short-term exposures are often twice the short-term reference value (100 ppm; 15-min time-weighted average). These processes also involve exposure to styrene oxide, which is a suspected carcinogen. Use of low-emission resins reduces exposure during curing but not during lamination itself. The exposure of laminators can be reduced by use of combined, carefully planned, general and local ventilation, adequately designed work places and promotion of safe working habits. The best way of controlling exposures to styrene in the reinforced plastic industry in general would be to automate the processes and to use closed moulds.