A survey of dust concentrations in flax mills in Northern Ireland.

The concentrations in the air of total and of respirable (less than 7 microns equivalent diameter) dust were measured in 142 workrooms of 17 Northern Ireland flax spinning mills using a hexhlet air sampler. 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 ofmean log. concentrations followed in brackets by the respective antilogs. (mg./100 m.3 air) were as follows: