Section R. 325.60154 - Maximum allowable concentrationsRule 4.
(1) Maximum allowable concentrations of air contaminants based on a repeated 8-hour work day exposure are listed in tables 1 to 7 in R 325.60155 to R 325.60161.(2) A substance in tables 1 to 6 that is preceded by the letter A, C, S, or STEL is an especially hazardous contaminant and all the following precautions shall be taken: (a) If the substance is preceded by the letter "A", then an employer shall ensure that an employee or any part of an employees anatomy is not exposed to, or allowed to come in contact with, the substance by means of any respiratory, oral, or skin route.(b) If the substance is preceded by the letter "C", then its MAC means the highest concentration at which an employer may allow a person to be exposed at any time unless noted otherwise. This concentration is commonly referred to as a "ceiling."(c) If the substance is preceded by the letter "S", then an employer shall ensure that precautions are taken to prevent skin absorption.(d) If the substance is preceded by "STEL", then it means the STEL listed. For example, an employee's 15-minute, time-weighted average exposure, shall not be exceeded at any time during a work day. The STEL is commonly referred to as the "short-term exposure limit."Mich. Admin. Code R. 325.60154