1910.134(d)(3)(i)(B): Respirator Maximum Use Concentration
Employers must select a respirator that keeps the employee's exposure, measured outside the respirator, at or below the maximum use concentration (MUC). MUCs must not be applied to IDLH conditions, and when the calculated MUC exceeds the IDLH level or the cartridge or canister limits, the maximum MUC must be set at that lower limit.
Key takeaways
- 1910.134(d)(3)(i)(B) is part of OSHA's general industry standards (29 CFR Part 1910, Subpart I).
- OSHA cited it 16 times in the last 3 years, in 16 inspections, with $51,897 in current penalties.
- Most citations: TN (3), MD (3), NY (2).
- Related part: 1910.134(d) Selection of respirators (573 citations).
- Free 5-minute toolbox talk for your crew below.
In this article
What this rule covers
29 CFR 1910.134(d)(3)(i)(B) ("Maximum Use Concentration (MUC)") is one requirement inside 1910.134 Respiratory protection, an OSHA general industry standard (Part 1910, Subpart I). The official text below is copied word for word from the Electronic Code of Federal Regulations (eCFR). The numbers, injury cases and training on this page show how OSHA enforces it on real job sites.
Official text
(B) Maximum Use Concentration (MUC). 16 citations
(1) The employer must select a respirator for employee use that maintains the employee's exposure to the hazardous substance, when measured outside the respirator, at or below the MUC.
(2) Employers must not apply MUCs to conditions that are immediately dangerous to life or health (IDLH); instead, they must use respirators listed for IDLH conditions in paragraph (d)(2) of this standard.
(3) When the calculated MUC exceeds the IDLH level for a hazardous substance, or the performance limits of the cartridge or canister, then employers must set the maximum MUC at that lower limit.
Source: eCFR, text current as of 2026-10-15. Read all of 1910.134.
Where and how often it was cited
| Year | Citations |
|---|---|
| 2024 | 4 |
| 2025 | 8 |
| 2026 | 4 |
Top states: TN (3), MD (3), NY (2), OK (2), NC (2)
Largest penalties
| Employer | Location | Penalty for this rule |
|---|---|---|
| ROCK-IT NATURAL STONE | WISTER, OK | $12,500 |
| MID-CONTINENTAL RESTORATION CO., INC. | OKLAHOMA CITY, OK | $9,344 |
| GA TELESIS LANDING GEAR SERVICES, LLC | MIAMI, FL | $9,268 |
| DAVIS-STANDARD, LLC | PAWCATUCK, CT | $6,000 |
| THE LAKEWOOD BRICK AND TILE COMPANY | LAKEWOOD, CO | $6,000 |
Free toolbox talk
A 5-minute crew talk on 1910.134(d)(3)(i)(B), plus alerts when this rule changes. Free.
OSHA interpretation letters
None exist. OSHA has not published a letter of interpretation for 1910.134(d)(3)(i)(B).
Related parts of this rule
- 1910.134(d) Selection of respirators 573 citations
- 1910.134(d)(1) General requirements 477 citations
- 1910.134(d)(1)(iii) 312 citations
- 1910.134(d)(1)(i) 88 citations
- 1910.134(d)(3) Respirators for atmospheres that are not IDLH 86 citations
- 1910.134(d)(1)(ii) 74 citations
- 1910.134(d)(3)(iii) 53 citations
- 1910.134(d)(3)(iii)(B) 52 citations
- 1910.134(d)(3)(i) 28 citations
- 1910.134(d)(2) Respirators for IDLH atmospheres 10 citations
- 1910.134(d)(2)(i) 9 citations
- 1910.134(d)(3)(i)(A) Assigned Protection Factors (APFs) 3 citations
Get your crew competent
Trainers on Black Belt Safety: Marc Harvey, Dana Reyes
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Frequently asked questions
What is the MUC used for?
Selecting a respirator that keeps exposure, measured outside the respirator, at or below the MUC.
Can MUCs be used in IDLH conditions?
No. Employers must use respirators listed for IDLH conditions in paragraph (d)(2) instead.
What if the calculated MUC is higher than the IDLH level?
The maximum MUC must be set at the lower limit.
About this page
Sources
- 29 CFR 1910.134 (eCFR), text current as of 2026-10-15
- U.S. Department of Labor enforcement data: OSHA inspections, citations and accident records, copied nightly; data as of 2026-10-20
3-year window. Federal OSHA only; state-plan rules are not counted. Plain-language text is a summary, not legal advice; the official text controls. Black Belt Safety is not part of OSHA or the Department of Labor.