HSL was asked by HSE to investigate how the risks of pneumoconiosis vary for different patterns of exposure in coalminers. Five exposure scenarios were presented, based on those used as examples of the time-weighting method for exposure limits in the proposed new legislation on control of inhalable dust in coal mines. The following shift patterns were investigated:
HSL investigated the influence of the change in shift patterns on the risk of category 2 pneumoconiosis by means of a mathematical model. This model described the exposure-dose relationship, where the dose is the burden of coalmine dust in the human lungs. For humans, the pulmonary adverse effect of coal dust is the impairment of normal functions of the alveolar region (i.e. the blood-air barrier). This region is normally kept clean and sterile by scavenging cells, the macrophages, which ingest foreign matters and clear them from the lung. However, coal dust is predominantly retained in the interstitial space, i.e. the matrix of supporting tissue of the lung and therefore is prevented from being removed by macrophages. The accumulation of coal dust in the interstitial space eventually impairs normal lung functions.
The calculations indicated that the reduction in the dust concentration required by the proposed time-weighting model would lead to either a reduction in pneumoconiosis risk or at least maintenance of the level of risk at the baseline level in all the scenarios. The model simulations have also indicated that the clearance of coal dust from the lungs is also a sensitive factor affecting the risk of pneumoconiosis.