Respirable dust standard when quartz is present.

When the respirable dust in the mine atmosphere of the active workings to which a Part 90 miner is exposed contains more than 5 percent quartz, the operator shall continuously maintain the average concentration of respirable dust in the mine atmosphere during each shift to which a Part 90 miner is exposed at or below a concentration of respirable dust computed by dividing the percent of quartz into the number 10. The application of the formula shall not result in a respirable dust standard in excess of 1.0 milligrams per cubic meter of air. Concentrations shall be expressed in milligrams per cubic meter of air as measured with an approved sampling device and in terms of an equivalent concentration determined in accordance with §90.206 (Approved sampling devices; equivalent concentrations).

EXAMPLE: The respirable dust associated with a Part 90 miner contains quartz in the amount of 20%. Therefore, the average concentration of respirable dust in the mine atmosphere associated with that Part 90 miner shall be continuously maintained at or below 0.5 milligrams of respirable dust per cubic meter of air (10/20=0.5 mg/m(super)3).