Use of history science methods in exposure assessment for occupational health studies

Aims: To show the power of history science methods for exposure assessment in occupational health studies, using the dry cleaning industry in Denmark around 1970 as the example. Methods: Exposure data and other information on exposure status were searched for in unconventional data sources such as the Danish National Archives, the Danish Royal Library, archives of Statistics Denmark, the National Institute of Occupational Health, Denmark, and the Danish Labor Inspection Agency. Individual census forms were retrieved from the Danish National Archives. Results: It was estimated that in total 3267 persons worked in the dry cleaning industry in Denmark in 1970. They typically worked in small shops with an average size of 3.5 persons. Of these, 2645 persons were considered exposed to solvents as they were dry cleaners or worked very close to the dry cleaning process, while 622 persons were office workers, drivers, etc in shops with 10 or more persons. It was estimated that tetrachloroethylene constituted 85% of the dry cleaning solvent used, and that a shop would normally have two machines using 4.6 tons of tetrachloroethylene annually. Conclusion: The history science methods, including retrieval of material from the Danish National Archives and a thorough search in the Royal Library for publications on dry cleaning, turned out to be a very fruitful approach for collection of exposure data on dry cleaning work in Denmark. The history science methods proved to be a useful supplement to the exposure assessment methods normally applied in epidemiological studies.