Investigation into the impact of introducing workplace aerosol standards based on the inhalable fraction
Since the late 1970s, there has been considerable discussion about describing human aerosol exposure in terms of a scientific criterion based on the efficiency with which particles are inhaled through the nose and/or mouth during breathing. As international agreement on the quantitative form of this criterion has emerged, progress is quickening towards workplace and environment aerosol standards in which the current ‘total aerosol’ approach will be replaced by one based on ‘inhalability’. Wind tunnel investigations of a range of personal samplers currently used in workplaces for sampling ‘total’ aerosol have shown that many of these are not adequate for collecting the inhalable fraction. Such experimental evidence is supported by considerations of the physical sampling characteristics of the various samplers. Studies have been conducted to investigate workers' exposures to ‘total’ and inhalable aerosol in the workplaces of several industries in several countries, using side-by-side sampling in which participating workers wear two samplers, one for ‘total’ aerosol and the other for inhalable aerosol. The results from the several hundred sample pairs taken so far show that the level of exposure based on inhalable aerosol consistently exceeds that for ‘total’ aerosol. The observed ratios between the inhalable and ‘total’ aerosol exposures range from 1.2 to > 3, tending to be greater for workplaces where the aerosol is expected to be coarser. Such results may be used to assess the impact on industry of new limit values based on inhalable aerosol. It is clear that measured levels of exposure will tend to rise, so that there will be generally increased proportions of exposure measurements where levels will come close to, or exceed, current exposure limits. Those proportions may be greater still if new, lower limit values for ‘total’ aerosol currently under consideration for some substances are implemented. This paper examines these issues by reference to examples of exposure data taken from a range of industries and proposes options for how such information might influence the setting of future occupational exposure limits.