Maximum use concentration (MUC)
The highest concentration a respirator can be used in: its APF multiplied by the exposure limit.
Definition, in the source's words
29 CFR 1910.134(b)(opens ecfr.gov in a new tab)“Maximum use concentration (MUC) means the maximum atmospheric concentration of a hazardous substance from which an employee can be expected to be protected when wearing a respirator, and is determined by the assigned protection factor of the respirator or class of respirators and the exposure limit of the hazardous substance. The MUC can be determined mathematically by multiplying the assigned protection factor specified for a respirator by the required OSHA permissible exposure limit, short-term exposure limit, or ceiling limit.”
What it means
MUC = APF × exposure limit. If the result is above the IDLH level or the cartridge's performance limit, the maximum is set at that lower limit (1910.134(d)(3)(i)(B)(3)). MUCs never apply to IDLH conditions, which need the respirators listed in 1910.134(d)(2).
Example
Half mask, APF 10; PEL 50 ppm. MUC = 10 × 50 = 500 ppm. If the substance's IDLH were 300 ppm, the maximum would be set at 300 ppm instead.
Where it appears on the exam
ASP: ASP11 Domain 6, Industrial Hygiene and Occupational Health
Practice: Respiratory Protection
CSP: CSP11 Domain 3, Risk Management
Practice: PPE Hazard Assessment and Selection
Questions
- How do you calculate MUC?
- Multiply the respirator's assigned protection factor by the OSHA exposure limit (PEL, short-term limit or ceiling).
Related
- Assigned protection factor (APF)
- IDLH (immediately dangerous to life or health)
- Ceiling limit (C)
- Regulation: 29 CFR 1910.134
Checked 2026-10-16. Spot a problem? Email hello@passcited.com.