Carbon Monoxide Headquarters


Allowable (Legal) Limits for CO:



Occupational Safety & Health Administration, USA (OSHA) (for industrial situations) -

Permissible Exposure Limit (PEL, by TWA) - 50 ppm, 8 hrs.

Old PEL Standard (by TWA) - 35 ppm, 8 hrs.

Threshold Limit Value (TLV, by TWA) - 25 ppm (29 mg/cu. m)
(recommended by American Conference of Governmental & Industrial Hygienists [ACGIH]

Ceiling (max. value, 15 min.) - 200 ppm (229 mg/cu. m)

Michigan Occupational Safety & Health Administration (MIOSHA) -

PEL (Industry, by TWA) - 35 ppm, 8 hrs. (38.5 mg/cu. m)

PEL (Construction, by TWA) - 50 ppm, 8 hrs. (55 mg/cu. m)

Ceiling (max. value) - 200 ppm (229 mg/cu. m)

Environmental Protection Agency, USA (EPA) -

Domestic, outdoor air, all ages (TWA) - 9 ppm*, 8 hrs.

Domestic, outdoor air, all ages (TWA) - 35 ppm, 1 hr.

World Health Organization (WHO) -

Domestic, outdoor air, all ages (TWA) - 9 ppm*, 8 hrs.

American Gas Association -

Indoor air (leakage at a heat register) - 15 ppm

American Society of Heating, Refrigeration & Air Conditioning Engineers (ASHRAE) -

Indoor air (leakage at a heat register) - 9 ppm

Common Action Level -

Indoor air (most common CO level triggering action by local Authorities of Jurisdiction) - 9 ppm


TWA - Computed by making measurements at intervals over 8 hours, then adding the sums of the concentrations and the intervals, and dividing by 8 hours (480 min.).
* Based on several published studies of people with coronary ischemic disease showing ECG changes during moderate exercise when breathing concentrations of CO giving 3% COHb.


...... last changed 08/23/00

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