Occupational Exposure Limit Quick Reference

Compare legally enforceable OSHA limits with current health-based guidance from ACGIH and NIOSH. Always verify against the latest published tables before use in compliance decisions.

29 CFR 1910.1000 Table Z ACGIH TLV Booklet (current year) NIOSH Pocket Guide to Chemical Hazards

Understanding Exposure Limits

Legal Standard

OSHA PEL

Permissible Exposure Limit — legally enforceable OSHA standard. Expressed as 8-hr TWA unless otherwise stated. Non-compliance results in citation and penalty. Most PELs set in 1971; rarely updated since.

Professional Guidance

ACGIH TLV

Threshold Limit Value — ACGIH professional recommendation. More current than PELs. Three types: TWA (8-hr), STEL (15-min short-term), and Ceiling (C, must never be exceeded).

Research-Based Guidance

NIOSH REL

Recommended Exposure Limit — NIOSH research-based recommendation. Forms the scientific basis for OSHA rulemakings. Often more protective than PELs. Not legally enforceable.

Emergency Threshold

IDLH

Immediately Dangerous to Life or Health — maximum concentration from which escape within 30 minutes is possible without irreversible harm or impairment. Basis for respirator selection.

Exposure Averaging & Calculations

8-Hour TWA Formula

TWA = (C₁T₁ + C₂T₂ + … + CₙTₙ) ÷ 8

Where C = concentration (ppm or mg/m³) and T = duration (hours). Total must equal 8 hours; periods with no exposure counted as zero concentration.

STEL (Short-Term Exposure Limit)

15-minute average — max 4 excursions per shift — ≥60 min between excursions

STEL excursions must not exceed 3× the TLV-TWA for more than 30 min/shift and must never exceed 5× the TLV-TWA at any time.

Ceiling (C)

Instantaneous — must NOT be exceeded at any time

Sampled over a 15-minute period for analytical purposes only. Any exceedance constitutes overexposure regardless of TWA compliance.

Noise Exposure Limits

Duration (hrs/day)	OSHA PEL (dBA)	ACGIH TLV (dBA)	Notes
8	90	85	Action Level = 85 dBA (HCP required per 29 CFR 1910.95)
6	92	87
4	95	90
3	97	92
2	100	95
1.5	102	97
1	105	100
0.5	110	105
0.25 or less	115	110	OSHA ceiling: 115 dBA. Impact/impulsive noise: 140 dBA peak pressure level

Exchange Rate Difference: OSHA uses the 5 dB exchange rate (halving time = 5 dB); ACGIH uses the more protective 3 dB exchange rate (equal energy principle). The 3 dB rate is the internationally recognised scientifically correct method and is used by NIOSH and most international standards bodies.

Common Chemical Exposure Limits

Chemical	CAS #	OSHA PEL	ACGIH TLV-TWA	NIOSH REL	IDLH	Notes
Acetone	67-64-1	1000 ppm	250 ppm 500 STEL	250 ppm	2500 ppm	Skin absorption
Ammonia	7664-41-7	50 ppm	25 ppm 35 STEL	25 ppm	300 ppm	IDLH revised 2014
Benzene	71-43-2	1 ppm	0.5 ppm	0.1 ppm	500 ppm	A1 Human carcinogen; 29 CFR 1910.1028
Carbon Monoxide	630-08-0	50 ppm	25 ppm	35 ppm 200C	1200 ppm	Odourless; CO detector required in confined spaces
Chlorine	7782-50-5	1 ppm (C)	0.5 ppm 1 STEL	0.5 ppm 1C	10 ppm
Ethanol	64-17-5	1000 ppm	1000 ppm	—	3300 ppm
Formaldehyde	50-00-0	0.75 ppm 1.0 STEL	0.1 ppm (C)	0.016 ppm	20 ppm	A2 Suspected carcinogen; 29 CFR 1910.1048
Hexane (n-)	110-54-3	500 ppm	50 ppm	50 ppm	1100 ppm	Peripheral neuropathy risk
Hydrogen Sulfide	7783-06-4	20 ppm 50C	1 ppm 5 STEL	1 ppm 10C	50 ppm	Olfactory fatigue at high concentrations
Isopropyl Alcohol	67-63-0	400 ppm	200 ppm 400 STEL	400 ppm	2000 ppm
Lead	7439-92-1	0.05 mg/m³	0.05 mg/m³	0.05 mg/m³	100 mg/m³	Blood lead monitoring required; 29 CFR 1910.1025
Mercury (vapour)	7439-97-6	0.1 mg/m³ (C)	0.025 mg/m³	0.05 mg/m³ 0.1C	10 mg/m³	Skin/CNS hazard
Methanol	67-56-1	200 ppm	200 ppm 250 STEL	200 ppm	6000 ppm	Skin absorption; optic nerve damage
Methylene Chloride	75-09-2	25 ppm 125 STEL	50 ppm	0.5 ppm 1C	2300 ppm	Converted to CO in body; 29 CFR 1910.1052
Silica, Crystalline	14808-60-7	0.05 mg/m³	0.025 mg/m³	0.05 mg/m³	25 mg/m³	A1 carcinogen; silicosis risk; 29 CFR 1910.1053
Styrene	100-42-5	100 ppm 200C	20 ppm 40 STEL	50 ppm 100C	700 ppm	A4 (inadequate animal data)
Toluene	108-88-3	200 ppm 300C	20 ppm	100 ppm	500 ppm	CNS/reproductive hazard
Trichloroethylene	79-01-6	100 ppm	10 ppm 25 STEL	2 ppm certified C	1000 ppm	A2 carcinogen; 29 CFR 1910.1028
Vinyl Chloride	75-01-4	1 ppm	1 ppm	Lowest feasible	10 ppm	Human carcinogen (angiosarcoma); 29 CFR 1910.1017
Xylene (o,m,p-)	1330-20-7	100 ppm	100 ppm 150 STEL	100 ppm	900 ppm

Disclaimer & Currency

Disclaimer: Exposure limits shown reflect published values at time of authorship. Always verify against the latest OSHA 29 CFR 1910.1000 Table Z, the current-year ACGIH TLV Booklet, and the NIOSH Pocket Guide to Chemical Hazards before making compliance or health decisions. PELs are legally enforceable minimums; TLVs and RELs represent current health-based guidance and are frequently more protective than PELs. Substances shown in red have OSHA substance-specific standards that supersede Table Z. This card is for reference and training purposes only and does not constitute legal or medical advice.