A York Respirable Dust Sampler, model IU 3799 (Ametek, Florida), containing apreweighed 37 mm type A/E glass fibre filter (VWR, Alberta) was hung from the shirt collar of the workers, and connected with tubing to a Gilian Gil-Air Personal Sampler (Gilian Instruments Corporation, New Jersey), which hung on a washable belt at the waist. The air pump was set to run at a rate of 1.7 L/min. The subject wore the personal sampler for the entire time spent working in the barn. On completion of the barn work, the subject was asked to estimate the time spent at each of the four production stages and the time spent on each activity. The most common activities were feeding, cleaning, breeding and pig treatments such as injections and processing of piglets. Dust sample collection for respirable and total dust occurred over an 8 h period.
For both across-shift and follow-up, arithmetic means were calculated to estimate average exposure in the barn. To estimate the average annual exposure, the arithmetic mean for the number of zones in the barn was calculated, and then the arithmetic mean of the means for summer and winter measurements was calculated. Because there was no significant association with 1989/90 environmental measurements, the environmental measurements obtained in 1994/95 were used in the statistical analysis.