The effect of exposure to man made vitreous fibers (MMVF) on workers in the prefabricated wooden house manufacturing industry was investigated. A model was developed to measure the past exposure to MMVF of 478 insulators among a staff of 2,807 workers at 11 factories in Sweden. The insulators who had a mean employment time of 9.6 years and never used respirators were identified as the workers at greatest risk of exposure to MMVF. One hundred and twenty samples were taken of airborne fiber in 11 facilities to determine current exposure levels. Using the model to estimate past exposure the highest mean fiber exposure level for insulators was calculated as 0.18 fiber/milliliter (f/ml), which occurred during the mid 1970s, compared to 0.10 f/ml at the end of the 1980s and the early 1960s. Changes in production rate, improved ventilation control, and the surface area of the total amount of MMVF sheets handled by the insulator were the most important variables in the model. No increased risk of lung cancer was found for the insulators who were presently working in the house prefabrication industry.

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