1910.1000(a)(1): Ceiling Exposure Limits
Employers must make sure an employee's exposure to any Table Z-1 substance with a limit marked "C" never exceeds that ceiling limit. If instantaneous monitoring is not feasible, the ceiling is assessed as a 15-minute time weighted average that must not be exceeded at any time during the workday.
Key takeaways
- 1910.1000(a)(1) is part of OSHA's general industry standards (29 CFR Part 1910).
- OSHA cited it 10 times in the last 3 years, in 10 inspections, with $51,612 in current penalties.
- Most citations: WI (2), IN (2), TX (2).
- Related part: 1910.1000(a) Table Z-1 (150 citations).
- Free 5-minute toolbox talk for your crew below.
In this article
What this rule covers
29 CFR 1910.1000(a)(1) ("Substances with limits preceded by “C”—Ceiling Values") is one requirement inside 1910.1000 Air contaminants, an OSHA general industry standard (Part 1910). 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
(1) Substances with limits preceded by “C”—Ceiling Values. An employee's exposure to any substance in Table Z-1, the exposure limit of which is preceded by a “C”, shall at no time exceed the exposure limit given for that substance. If instantaneous monitoring is not feasible, then the ceiling shall be assessed as a 15-minute time weighted average exposure which shall not be exceeded at any time during the working day. 10 citations
Source: eCFR, text current as of 2026-10-15. Read all of 1910.1000.
Where and how often it was cited
| Year | Citations |
|---|---|
| 2023 | 1 |
| 2024 | 3 |
| 2025 | 3 |
| 2026 | 3 |
Top states: WI (2), IN (2), TX (2), NC (1), CO (1)
Largest penalties
| Employer | Location | Penalty for this rule |
|---|---|---|
| CACIQUE FOODS LLC | AMARILLO, TX | $16,550 |
| EAGLE RAILCAR SERVICES | ORANGE, TX | $9,646 |
| 154625 - ALAMANCE FOODS, INC. | GLEN RAVEN, NC | $8,000 |
| 68502 - MILLS FENCE COMPANY INC | WALTON, KY | $6,300 |
| RUBY'S AUTO BODY INC. | LA JUNTA, CO | $3,547 |
Free toolbox talk
A 5-minute crew talk on 1910.1000(a)(1), plus alerts when this rule changes. Free.
OSHA interpretation letters
None exist. OSHA has not published a letter of interpretation for 1910.1000(a)(1).
Related parts of this rule
- 1910.1000(a) Table Z-1 150 citations
- 1910.1000(a)(2) Other substances—8-hour Time Weighted Averages 121 citations
Get your crew competent
Trainers on Black Belt Safety: Marc Harvey, Dana Reyes
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Frequently asked questions
What does a "C" mean in Table Z-1?
It is a ceiling value that must at no time be exceeded.
What if instant monitoring is not possible?
The ceiling is assessed as a 15-minute time weighted average exposure.
Can the 15-minute average be exceeded?
No. It must not be exceeded at any time during the working day.
About this page
Sources
- 29 CFR 1910.1000 (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 2026-10-21
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.