Section R. 325.2403 - Definitions pertaining to contaminantsRule 3. As used in these rules:
(a) "Maximum allowable concentration" or "MAC" means the threshold limit value or the time-weighted average 8-hour airborne concentration of a contaminant to which a person may be safely exposed. R 325.2413 to R 325.2419, tables 1 to 7, refer to the MAC of a particular contaminant.(b) "Mg/M3" means milligrams of particulate per cubic meter of air.(c) "Mppcf' means millions of particulates per cubic foot of air based on impinger samples counted by light field microscopic techniques.(d) "Non-respirable atmosphere" means an atmosphere which contains insufficient oxygen, or an elevated level of contaminants, which may render a person incapable of self-rescue.(e) "Ppm" means parts of vapor or gas per million parts of air by volume at 25 degrees Celsius and 760 millimeters of mercury pressure.(f) "Source" means a process or equipment which releases a contaminant into the air in concentrations exceeding the MAC.Mich. Admin. Code R. 325.2403