Michigan Administrative Code
Department - Environmental Quality
Air Quality Division
Part 2 - AIR USE APPROVAL
Section R. 336.1232 - Methodology for determining initial threshold screening level
Current through Vol. 24-04, March 15, 2024
Rule 232.
(1) The initial threshold screening level (ITSL) for each toxic air contaminant shall be determined as follows:
ITSL = OEL divided by 100
Where the OEL is the lowest value of either the national institute of occupational safety and health (NIOSH) recommended exposure level listed in the NIOSH pocket guide to chemical hazards or the time-weighted average or ceiling threshold limit value listed in the TLVs and BEIs. The NIOSH Pocket Guide to Chemical Hazards is adopted by reference in R 336.1902. TLVs and BEIs. Threshold Limit Values for Chemical Substances and Physical Agents, and Biological Exposure Indices, is adopted by reference in R 336.1902.
Where:
UF = A value from 1 to 10 determined on a case-by-case basis, considering type and severity of effect.
The ITSL may be determined on a case-by-case basis using NOAELs or LOAELs from repeated dose studies other than 7-day studies.
Where:
WA = Body weight of experimental animal in kilograms (kg).
IA = Daily inhalation rate of experimental animal in cubic meters/day.
b = Absorption efficiency by the oral route of exposure.
a = Absorption efficiency by the inhalation route of exposure.
UF = A value from 1 to 10 determined on a case-by-case basis, considering type and severity of effect.
The ITSL may be determined on a case-by-case basis using NOAELs or LOAELs from repeated dose studies other than 7-day studies.
Where:
LC50 = A calculated concentration of a chemical in air to which exposure for a specific length of time is expected to cause death in 50% of a defined experimental animal population.
Where:
LD50 = The dose of a chemical that has been calculated to cause death in 50% of a defined animal population.
WA = Body weight of experimental animal in kilograms (kg).
IA = Daily inhalation rate of experimental animal in cubic meters/day.
(2) The averaging times to be used for ITSLs are as follows:
An obvious error in R 336.1232 was corrected at the request of the promulgating agency, pursuant to Section 56 of 1969 PA 306, as amended by 2000 PA 262, MCL 24.256. The rule containing the error was published in Annual Administrative Code Supplement, 2016. The memorandum requesting the correction was published in Michigan Register, 2020 MR 24.