Underground » Health and Safety
Monitoring of personal respirable dust exposure is a crucial step in eliminating the coal mine workers pneumoconiosis (CWP) disease from the Australian coal mining industry. The standard personal monitoring is conducted in a breathing zone which is defined as the area within 0.3 m radius of a worker's nose and mouth. Current samples taken within the breathing zone are usually obtained by fastening a sampling device or tube to a lapel position of the worker. In modern Australian coal mining practices, various respirators including powered air-purifying respirators (PAPRs) and disposable dust masks are supplied to protect coal mine workers from exposures. If a respirator including PAPR is worn, personal dust monitoring samples should be taken outside the respirator as per the current Australian Standard/mining legislation.
The objectives of this project were to investigate the spatial variability of dust exposure levels in the breathing zone and evaluate the effectiveness of respirators on personal dust exposure levels. The latest Personal Dust Monitor, PDM3700, were mainly used for laboratory and field studies in the project, not only providing mass-based real-time dust exposure during sampling testing but also enabling dust sampling inside the respirator due to its small sampling head.
A large volume dust testing chamber with capability of varying air velocity and dust load inside the chamber was designed and constructed for laboratory studies. The spatial variability of dust concentrations in the breathing zone was investigated by parallel sampling at the nose and lapel positions. Laboratory study results show that there is not a significant difference (< 4%) in dust concentrations measured at the nose and lapel under various testing parameters and conditions. Although there is a marginally noticeable difference in measured dust concentrations between nose and lapel sampling positions, the inherent systematic difference between dust sampling units used contribute a similar or above effect on the spatial discrepancy.
It was observed during field studies that spatial variability of dust levels and imprecision of the current personal dust samplers in taking an individual measurement has a greater impact than swapping sampling location from nose to lapel in breathing zone or reciprocally.
Efforts were made to test and evaluate the performance of various respirators including a PAPR and disposable P2 masks (valved and non-valved). Both laboratory and field results show that the PAPR has excellent filtration efficiency and protection performance, and no dust was detected inside the unit if worn properly. Laboratory setup was developed to test P2 masks either with inhaling action alone induced by a suction pump or under both inhaling and exhaling actions using a breathing simulator. It was found that while dust concentrations both inside and outside P2 masks increase with the upsurge of dust loads and the decreasing protection factors of the tested P2 masks are still at least 2 to 3 times of the required protection factor value of 10 if fitted tightly. The results also show that the non-valved P2 mask has better protection factors than the valved one. Testing of P2 masks with artificially induced leakage shows that protection factors of the P2 masks decrease significantly under varied levels of induced leakage. Introducing moisture during exhaling process has no significant effects on the protection factor of tested P2 masks.
All test results have clearly indicated that if the P2 mask is fit or worn properly, it is able to provide a good protection for coal mine workers working under various dust loads conditions.