(a) Surface and underground mines. When an abrasive blasting operation is performed, all exposed miners shall properly use respirators approved for abrasive blasting by NIOSH under 42 CFR part 84, or the operation shall be performed in a totally enclosed device with the miner outside the device.

(b) Underground areas of underground mines. Silica sand or other materials containing more than 1 percent free silica shall not be used as an abrasive substance in abrasive blasting.