The study group comprised all persons working in the production unit of nine randomly chosen companies. There was no selection based on exposure intensity, size of the factories, health complaints among employees, or other factors. Data were collected from 1,047 persons. According to the employers’ information, we examined all persons from the different workshops employed at the time period 1996/1998. However, we had no possibility to check the list of all persons employed and to compare them with the list of persons we examined. Characteristics of the study group are presented in Table 1.
The data concerning dust measurements were gathered from 1991 to 1997. Dust measurements were performed according to the Technical Guidelines for the Detection and Measurement of Hazardous Substances. The mean sampling time was 1.97 h (range, 0.16 to 3.8 h). The cross-sectional study with the data collection concerning lung function, occupational history, and smoking habits took place in the years from 1996 to 1998. Three subgroups were defined within the study group. Group 1 consists of control persons of each company from the management departments. Group 2 had moderate exposure (maintenance workers, electricians, mechanics). Group 3 consists of workers from the production workshops (paper machine, combiner) and was classified as having high exposure. Due to differences in the exposure intensity between the nine companies, a cumulative exposure index was generated for describing the individual exposure. The mean of the dust and fiber concentrations of each company were multiplied by the individual time of exposure of persons with high exposure. In cases of moderate exposure, the mean dust and fiber concentrations of each company was divided by four and multiplied by the individual time of exposure. According to the information from technical experts, this attenuation factor best represents the intermittent and lower exposure of those workers. For each participant, a cumulative exposure index was available for dust and for fibers. Because dust measurements for the respirable fraction (diameter < 5 μm) was not available from each company, no exposure index was calculated for this fraction.
Table 1—Number, Age, Sex, Smoking Habits, and Duration of Exposure in Workers
|Age, yr||36.3 ± 11.3||39.0 ± 10.0||38.6 ± 9.9|
|Exposure, yr||13.1 ± 10.5||13.0 ± 8.7|