Neither the distribution of total nor of respirable dust concentrations (mg./100 m.³ air) measured in each of four large workrooms conformed to the normal (or Gaussian) distribution, but it is shown that the logarithms (to the base 10) of these concentrations are normally distributed. In order to make valid statistical comparisons between the dustiness of the different types of room, mean log. concentrations are therefore used.

The mean log. concentrations of total and of respirable dust, and the 95% confidence limits derived from these, were calculated for each room surveyed. For total and respirable dust the ranges of mean log. concentrations followed in brackets by the respective antilogs. (mg./100 m.³ air) were as follows: [Table: see text] Thus, dust concentrations varied widely within each category of room, although in general the pre-preparing rooms had the highest levels followed by other preparing rooms, other finishing rooms, and wet finishing rooms, in that order.