OSHA PELs + NIOSH RELs
OSHA Permissible Exposure Limits (PELs) are the legally binding federal air-contaminant limits (Table Z-1 / Z-2 / Z-3). NIOSH Recommended Exposure Limits (RELs) are advisory, often more protective and more current. ACGIH TLVs are copyrighted and not reproduced here.
PELs are binding but frozen — RELs are advisory but current
OSHA PELs are legally enforceable under the OSH Act (29 U.S.C. § 651 et seq.), codified in 29 CFR 1910.1000 Table Z-1 / Z-2 / Z-3. But most PELs remain at their 1971 levels (adopted wholesale from the 1968 ACGIH TLV list). OSHA's 1989 Air Contaminants Standard, which would have modernized ~400 limits, was vacated by the 11th Circuit Court of Appeals in 1992 (AFL-CIO v. OSHA, 965 F.2d 962) — so the federal floor has scarcely moved in over 50 years.
NIOSH RELs are advisory (not legally enforceable) but are science-based and frequently more protective than the corresponding PEL — see formaldehyde (REL 0.016 ppm vs PEL 0.75 ppm) or benzene (REL 0.1 ppm vs PEL 1 ppm) in the table below. When the REL is stricter than the PEL, OSHA's General Duty Clause § 5(a)(1) can still require employers to control a recognized hazard below the PEL.
PEL TWA
Permissible Exposure Limit — Time-Weighted Average (8-hour OSHA legal limit)
PEL C
PEL Ceiling — never to be exceeded
PEL STEL
Short-Term Exposure Limit — 15-min TWA max once per shift
Action Level
Typically 50% of PEL — triggers medical surveillance program enrollment
REL TWA
NIOSH Recommended Exposure Limit (not legally enforceable)
IDLH
Immediately Dangerous to Life or Health — atmospheric concentration warranting respirator and 30-min escape time
ACGIH TLVs + BEIs — copyrighted, not reproduced
ACGIH Threshold Limit Values (TLVs) and Biological Exposure Indices (BEIs) are the most scientifically current consensus values but are copyright-protected. Per project policy (public-domain sources only), no TLV or BEI numeric value is rendered on this page. Consult the official ACGIH publication directly for those figures. ACGIH TLV/BEI guidelines →
Hierarchy of controls (NIOSH) — most to least effective
- 1Elimination — physically remove the hazard.
- 2Substitution — replace with a less hazardous agent.
- 3Engineering controls — isolate people from the hazard (LEV, enclosure).
- 4Administrative controls — change how people work (rotation, training).
- 5PPE — respirators, gloves: last resort, never first.
An exposure below the PEL does not discharge the duty: the OSH Act requires feasible engineering/administrative controls first, with PPE only where those are insufficient (29 CFR 1910.134, substance-specific standards).
OSHA PEL + NIOSH REL by substance (40)
Values rendered verbatim from the source corpus. Red dot = IARC group 1 / NIOSH "lowest feasible" carcinogen. Sk = OSHA skin notation (percutaneous absorption). Cal/OSHA overrides shown where the state limit is stricter than federal.
| Substance | OSHA PEL (air) | OSHA action level | NIOSH REL | Cal/OSHA override |
|---|---|---|---|---|
| Lead, inorganic + compounds 29 CFR 1910.1025 + 1926.62 | 50 µg/m³ TWA (general industry); 50 µg/m³ (construction) | 30 µg/m³ TWA | <= 50 µg/m³ but recommends much lower | 10 µg/m³ TWA + AL 2 µg/m³ (final rule Standards Board approved Feb 15, 2024; effective Jan 1, 2025) |
| Asbestos (all fiber types) 29 CFR 1910.1001 + 1915.1001 + 1926.1101 | 0.1 f/cc TWA + 1.0 f/cc 30-min excursion | 0.1 f/cc TWA | 0.1 f/cc TWA (carcinogen — lowest feasible) | — |
| Benzene Sk 29 CFR 1910.1028 | 1 ppm TWA + 5 ppm STEL (15-min) | 0.5 ppm TWA | 0.1 ppm TWA + 1 ppm 60-min ceiling (carcinogen — lowest feasible) | — |
| Cadmium + compounds 29 CFR 1910.1027 + 1926.1127 | 5 µg/m³ TWA | 2.5 µg/m³ TWA | Lowest feasible (carcinogen) | — |
| Hexavalent chromium (Cr(VI)) Sk 29 CFR 1910.1026 (2006) | 5 µg/m³ TWA | 2.5 µg/m³ TWA | 0.2 µg/m³ TWA | — |
| Methylene chloride (DCM) Sk 29 CFR 1910.1052 | 25 ppm TWA + 125 ppm STEL | 12.5 ppm TWA | Lowest feasible (carcinogen IARC 2A) | — |
| Formaldehyde Group 1 29 CFR 1910.1048 | 0.75 ppm TWA + 2 ppm STEL | 0.5 ppm TWA | 0.016 ppm TWA + 0.1 ppm ceiling 15-min | — |
| Ethylene oxide (EtO) Group 1 29 CFR 1910.1047 (reproductive notice required) | 1 ppm TWA + 5 ppm STEL (15-min) | 0.5 ppm TWA | <0.1 ppm TWA + 5 ppm 10-min ceiling | — |
| Vinyl chloride monomer (VCM) Group 1 29 CFR 1910.1017 | 1 ppm TWA + 5 ppm 15-min ceiling | 0.5 ppm TWA | Lowest feasible (carcinogen) | — |
| 1,3-Butadiene Group 1 29 CFR 1910.1051 | 1 ppm TWA + 5 ppm STEL (15-min) | 0.5 ppm TWA | Lowest feasible | — |
| Inorganic arsenic Sk 29 CFR 1910.1018 | 10 µg/m³ TWA | 5 µg/m³ TWA | Ceiling 2 µg/m³ 15-min | — |
| Beryllium + compounds 29 CFR 1910.1024 (updated 2017) + 1915.1024 + 1926.1124 | 0.2 µg/m³ TWA + 2 µg/m³ STEL (15-min) | 0.1 µg/m³ TWA | Lowest feasible 0.05 µg/m³ ceiling 15-min (carcinogen) | — |
| Respirable crystalline silica 29 CFR 1910.1053 (2016 general industry) + 1926.1153 (construction) | 50 µg/m³ TWA | 25 µg/m³ TWA | 50 µg/m³ TWA (same as OSHA) | Engineered Stone Emergency Standard September 2023 (8 CCR 5204 enhanced) |
| Manganese (fume + dust) 29 CFR 1910.1000 Table Z-1 (general) | Ceiling 5 mg/m³ fume | — | 1 mg/m³ TWA + 3 mg/m³ STEL | — |
| Mercury (elemental vapor + inorganic) Sk 29 CFR 1910.1000 | Ceiling 0.1 mg/m³ organomercury; 0.05 mg/m³ TWA vapor inorganic | — | 0.05 mg/m³ TWA vapor | — |
| Toluene Sk 29 CFR 1910.1000 Table Z-2 | 200 ppm TWA + 300 ppm ceiling + 500 ppm peak | — | 100 ppm TWA + 150 ppm STEL | — |
| Xylene (mixed isomers) 29 CFR 1910.1000 Table Z-1 | 100 ppm TWA + 150 ppm STEL | — | 100 ppm TWA + 150 ppm STEL | — |
| Styrene 29 CFR 1910.1000 Table Z-2 | 100 ppm TWA + 200 ppm ceiling + 600 ppm peak | — | 50 ppm TWA + 100 ppm STEL | — |
| n-Hexane Sk 29 CFR 1910.1000 Table Z-1 | 500 ppm TWA (outdated) | — | 50 ppm TWA | — |
| Trichloroethylene (TCE) 29 CFR 1910.1000 Table Z-2 | 100 ppm TWA + 200 ppm ceiling + 300 ppm peak | — | Lowest feasible (carcinogen) | — |
| Tetrachloroethylene (PCE / perc) Group 2A 29 CFR 1910.1000 Table Z-2 | 100 ppm TWA + 200 ppm ceiling + 300 ppm peak | — | Lowest feasible (carcinogen) | — |
| Isocyanates — TDI 29 CFR 1910.1000 Table Z-1 (substance-specific surveillance) | 0.005 ppm TWA + 0.02 ppm ceiling 10-min | — | 0.005 ppm TWA + 0.02 ppm ceiling | — |
| Isocyanates — MDI | 0.02 ppm ceiling | — | 0.005 ppm TWA + 0.02 ppm ceiling | — |
| Carbon monoxide (CO) 29 CFR 1910.1000 Table Z-1 | 50 ppm TWA | — | 35 ppm TWA + 200 ppm ceiling | — |
| Hydrogen sulfide (H2S) 29 CFR 1910.1000 Table Z-2 | 20 ppm ceiling + 50 ppm peak 10-min once per shift | — | 10 ppm ceiling 10-min | — |
| Hydrogen cyanide (HCN) + cyanides Sk | 10 ppm TWA (4.7 ppm skin); cyanide salts 5 mg/m³ | — | Ceiling 4.7 ppm 10-min | — |
| Nitrogen dioxide (NO2) | 5 ppm ceiling | — | 1 ppm STEL | — |
| Ozone (O3) | 0.1 ppm TWA | — | 0.1 ppm ceiling | — |
| Chlorine (Cl2) | 1 ppm ceiling | — | 0.5 ppm TWA + 1 ppm STEL | — |
| Ammonia (NH3) | 50 ppm TWA | — | 25 ppm TWA + 35 ppm STEL | — |
| Sulfur dioxide (SO2) | 5 ppm TWA | — | 2 ppm TWA + 5 ppm STEL | — |
| Hydrogen fluoride (HF) | 3 ppm TWA | — | 3 ppm TWA + 6 ppm STEL | — |
| Nickel (metal + soluble compounds) Sk Group 1 | 1 mg/m³ TWA (metal); 0.1 mg/m³ TWA (insoluble compounds) | — | 0.015 mg/m³ TWA (carcinogen) | — |
| Hydrogen sulfide variants + sulfides (cumulative — listed separately above) | See us-pel-025 | — | — | — |
| Coke oven emissions (PAH as BSF) Group 1 29 CFR 1910.1029 | 150 µg/m³ TWA (BSF — benzene-soluble fraction) | 150 µg/m³ TWA | 0.1 mg/m³ TWA (cyclohexane-soluble) | — |
| Aerosolized petroleum (diesel exhaust EC) Group 1 | No specific OSHA PEL | — | Lowest feasible (carcinogen) | — |
| Methanol Sk | 200 ppm TWA | — | 200 ppm TWA + 250 ppm STEL | — |
| Cobalt (metal + compounds) Group 2A | 0.1 mg/m³ TWA | — | 0.05 mg/m³ TWA (carcinogen consideration) | — |
| Tungsten carbide (with cobalt binder) | Tungsten 5 mg/m³ TWA (insoluble compounds); see also Co 0.1 | — | 5 mg/m³ tungsten + Co 0.05 | — |
| Diacetyl + 2,3-pentanedione (popcorn lung agents) | None established | — | 5 ppb TWA (diacetyl) + 9.3 ppb TWA (2,3-pentanedione); 25 ppb STEL diacetyl | — |
Additional source fields not shown in the table (per substance, where present): IDLH air concentration, biological markers (BLL, CdB/CdU, urinary metabolites), antidote, EPA/TSCA 2024 actions, MSHA mining limits, NIOSH ototoxicity flag. These are retained in the corpus for cross-referencing with medical-surveillance triggers (sprint5).
Skin (Sk) + carcinogen notation
- Sk (skin): Substance may be absorbed through intact skin in toxicologically significant amounts. Air sampling alone underestimates dose — add biological monitoring and dermal protection.
- Carcinogen (red dot / IARC tag): for IARC group 1 agents and NIOSH "lowest feasible" carcinogens, there is no demonstrated safe threshold. The PEL is a legal ceiling, not a target — reduce exposure as far as feasible regardless of compliance.
🇺🇸 US ↔ 🇬🇧 UK structural comparison
| Dimension | 🇺🇸 US (OSHA) | 🇬🇧 UK (HSE EH40) |
|---|---|---|
| Legal basis | OSH Act → 29 CFR 1910.1000 Table Z (PEL binding) | COSHH reg 7 → WEL binding |
| Advisory tier | NIOSH REL (not enforceable, often stricter) | BMGV (non-binding review level) |
| Respirable crystalline silica | PEL 50 µg/m³ (0.05 mg/m³) | WEL 0.1 mg/m³ — US stricter |
| Lead | PEL 50 µg/m³ · removal BLL ≥60 µg/dL (GI) | CLAW suspension 30/50/60 µg/dL by group |
| Carcinogen duty | "Lowest feasible" + General Duty Clause § 5(a)(1) | ALARP (as low as reasonably practicable) |
| State variation | Cal/OSHA stricter (lead 10 µg/m³ from 2025) | Single UK-wide WEL set |
Silica and lead values cross-checked against the US corpus (us-pel-013, us-pel-001). The US RCS PEL of 50 µg/m³ equals 0.05 mg/m³ — stricter than the UK WEL of 0.1 mg/m³. The two countries use different lead threshold models (US air PEL + blood-lead removal vs UK CLAW suspension tiers).
Cal/OSHA — stricter state floor (Title 8 §5155)
Cal/OSHA Title 8 §5155 has stricter PELs than federal OSHA for many substances. Lead 2024 update (PEL 10 vs federal 50). Engineered stone silica 2023 emergency standard. Generally more protective.
https://www.dir.ca.gov/title8/5155.htmlLimits are legal floors, not safe levels
Meeting a PEL is the minimum legal compliance, not a guarantee of safety. Many PELs predate decades of toxicology; for carcinogens, sensitizers and the substances where the NIOSH REL is far below the PEL, control exposure as low as feasible. This is a reference table for occupational-health professionals, not a clinical or legal determination.
Why US exposure limits are fragmented
- ▸OSHA PELs mostly from 1971 (adopted 1968 ACGIH TLV list) — scientifically outdated
- ▸1989 OSHA PEL update VACATED by 11th Circuit in 1992 — federal hasn't updated since
- ▸NIOSH RELs more current but not legally enforceable
- ▸ACGIH TLVs + BEIs current science but COPYRIGHT — referenced only nominally
- ▸Cal/OSHA generally stricter (lead 2024, engineered stone 2023, etc.)
- ▸MSHA stricter for mining diesel exhaust
- ▸IDLH thresholds (NIOSH) for respirator selection
- ▸Skin notation flag for percutaneous absorption substances
- ▸Biological markers cross-referenced sprint5 medsurv triggers
U.S. exposure limits are FRAGMENTED + OFTEN OUTDATED. OSHA PELs (Permissible Exposure Limits) are the legally enforceable federal limits but most date from 1971 adoption of 1968 ACGIH TLV list — long out of date. NIOSH RELs (Recommended Exposure Limits) are scientifically current but NOT legally enforceable. ACGIH TLVs (Threshold Limit Values) + BEIs (Biological Exposure Indices) are most current scientifically but COPYRIGHT — referenced only nominally here per licensing constraints (cross-ref project policy exclusively-free-public-domain). Cal/OSHA has stricter PELs for several substances (lead 2024, e.g.). This catalog provides OSHA PEL + NIOSH REL for substances with established occupational surveillance + cross-refs sprint5 medsurv triggers + sprint14a-j PROT-* protocols. user_editable=true throughout.
Verification + provenance
- OSHA PELs originate from the original Table Z (1971), adopted from the 1968 ACGIH TLV list; substance-specific standards (29 CFR 1910.1001–1053) added later limits for benzene, lead, asbestos, silica, etc. The 1989 update was vacated in 1992, so most general-industry PELs have not changed since 1971.
- NIOSH RELs are dated to the NIOSH Pocket Guide and substance criteria documents; they are the advisory tier and are revised more recently than the federal PELs.
- Cal/OSHA overrides reflect specific state rulemaking (lead final rule approved Feb 15 2024, effective Jan 1 2025; engineered-stone silica emergency standard 2023).
- ACGIH TLVs/BEIs are deliberately excluded (copyright). A build-time scan confirmed the corpus contains no TLV/BEI numeric value in any rendered field.
- Source corpus generated 2026-05-25 (sprint-19 US). Confirm current OSHA / NIOSH / Cal-OSHA figures against the official sources below before operational use.
Official sources
- OSHA 29 CFR 1910.1000 Table Z-1 (general air contaminants — ~470 substances)
- OSHA 29 CFR 1910.1001-1053 Subpart Z (substance-specific standards)
- NIOSH Pocket Guide to Chemical Hazards (NPG)
- NIOSH Recommended Exposure Limits (RELs)
- Cal/OSHA Title 8 §5155 Permissible Exposure Limits (CA-specific stricter)
- ACGIH TLVs and BEIs (COPYRIGHT — referenced only)
American Conference of Governmental Industrial Hygienists publishes annually; not included verbatim here per project policy
- EPA IRIS (Integrated Risk Information System) — toxicological reference values
- ATSDR MRLs (Minimal Risk Levels)