Mining authorities around the world regulate respirable dust levels in underground coal mines. The majority of the current regulations set an overall permissible respirable dust level, which is subject to adjustment based on the levels of respirable quartz dust (silica) in the air. The largest variations between countries are in the frequency and locations of sampling, rather than in permissible levels of respirable dust. In China, respirable dust limits vary considerably, depending on the percentage of free silica in the dust. The overall limit is set at 3.5 mg/m3 if the free silica concentration is below 10%, but drops sharply to 0.3 mg/m3 if the free silica concentration exceeds 80%. In the UK, hard limits are set at 3.0 mg/m3 of respirable dust and 0.3 mg/m3 of respirable quartz dust, with adjustments to the results based on hours worked. Australia also mandates less than 3.0 mg/m3 of respirable dust, with an even lower 0.15 mg/m3 of respirable quartz dust.
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