MSHA, the Mine Safety and Health Administration, made the decision to follow in OSHA’s footsteps, dramatically cutting the allowable amount of respirable crystalline silica (aka RCS) in the atmosphere of mining processing facilities. According to MSHA, the permissible exposure limit (PEL) for respirable crystalline silica to 50 micrograms per cubic meter of air (µg/m3) for a full shift, calculated as an 8-hour time-weighted average (TWA) for all miners.