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Coke is produced by continuously baking bituminous coal in ovens in the absence of oxygen for around 16-17 hours. 1, 2 Hundreds of complex chemicals are generated during the coking process, with coal tar (phenols, cresols, naphthalene, benzene and its homologues, etc), light oil (benzene, toluene, the xylenes, etc) and gases (sulphur dioxide, nitrogen dioxide, ammonia, etc) being the main constituents of coke oven emissions. 1, 3 Such emissions are reported to have harmful health effects on workers. 4 Evidence from various epidemiological investigations shows that emissions can increase risk of lung and other cancers. 5- 9 Fewer studies have concentrated on lung function of coke oven workers. 10- 13 Some investigations have reported lower lung function and higher prevalence of bronchitis. 10, 12, 13
A lung function surveillance system has operated from 18 October 1978 at the recovery coke ovens of a steelworks. Since 2 July 1990, the surveillance system has continued with reselected surveillance parameters and modified assessment of smoking. Full utilisation of the information available necessitated separate analyses of the pre- and post-1990 data. One aim of this paper was to assess selection issues. Another was to conduct a cross sectional analysis on the pre-1990 data to assess determinants of the lung function of these coke oven workers.
MATERIALS AND METHODS
Study population
Of the 1727 subjects who ever worked in relatively highly exposed positions of coke ovens and hence were eligible to be registered in the surveillance system, 324 with no lung function measurements were excluded, along with 22 females (too few for useful analysis), and four subjects of unstated sex. There remained 1377 male subjects with at least one set of lung function measurements. The last sets (or the only sets) of lung function tests for all 1377 subjects were pooled to form the cross sectional database. This was a dynamic cohort, which allowed workers to freely join or withdraw.
More than half (738) of the subjects in the surveillance system began their coke oven work long before the surveillance system started. New starters were defined as those workers who had lung function tests within one year of commencing work at the coke ovens. A baseline analysis of the first (or only) sets of tests for 639 new starters was...