It is expected that the response rate among non-smokers will allow approximately 40 employees and 20 unexposed workers to be included in the sputum part of the study (study B). Based on the power calculations, prior experience and published studies, this will be enough to detect a difference in development between the two groups of the expected magnitude. In total, 150 workers are employed at SiC I and II (to be included in study A). It is planned to include the employees at Glomfjord (Nordland) SiC processing if the sample size from Porsgrunn is not sufficient. To ensure sufficient unexposed workers, the neighbouring Renewable Energy Corporation (REC) plant will be used to recruit controls if needed. The REC plant started production at about the same time and has a similar work-force to the study group.