Evaluation of half-mask respirator protection in styrene-exposed workers

Objective: The protection afforded by respirators to styrene (St)-exposed w orkers varies considerably. Our objective was to study the effective 'in th e field' reduction in St exposure obtained by negative-pressure half-mask r espirators worn by a group of fiberglass-reinforced plastics (FRP) workers. Protection was evaluated by measuring the reduction in urinary St (StU) ex cretion, Methods: Seven FRP workers not using respiratory protection devices were st udied for a week. External exposure to St was evaluated by personal passive sampling, and the internal dose by StU measurement. Then workers were aske d to use a half-mask respirator for a week for the entire morning half-shif t, and St exposure and internal dose were re-assessed. Results:. Mean environmental levels of St during the morning half-shift wer e 230-280 mg/m(3), i.e., about three times the current limit proposed by AC GIH; the difference among days was not significant. Using respirators was a ccompanied by a large inter-individual and also intra-individual variabilit y: the estimated reduction of StU values ranged from 30% to 90% (mean 60%). Mean StU values increased by 50% from Monday to Friday, while environmenta l St concentrations remained steady. Furthermore, the proportion of workers exceeding the biological equivalent exposure limit (BEEL) was 14% on Monda y, double (33%) on Thursday, and triple (43%) on Friday. These data suggest a decrease of protection during the week. Conclusions: The protection afforded by negative-pressure half-mask respira tors varies widely, which stresses the need to assess the effective reducti on of exposure whenever these devices are introduced for St-exposed workers . If respirators are to be re-used for several days, their performance must be evaluated during the last shift of use. Measurement of urinary excretio n of unmodified St proved a useful tool for the evaluation of respirator ef fectiveness in exposed workers.