Log-normality of distribution of occupational exposure concentrations to cobalt

In evaluating occupational exposures, the daily exposure levels of a worker are generally assumed to be distributed log-normally between days. When there are many workers in a job group, the individual worker's arithmetic means are assumed to be distributed log-normally. Using the cobalt exposure data in a hard metal factory, these assumptions were examined with the Shapiro-Wilk W test. The hypothesis of log-normality was accepted in all cases, while the hypothesis of normality was rejected in some cases.