30 CFR § 90.101
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).