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Allowable (Legal) Limits for Carbon Monoxide

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 Amer. Conf. of Governmental & Industrial Hygienists ACGIH)
Ceiling (max. value, 15 min.) – 200 ppm (229 mg/cu. m)

MI Occup. Safety & Health Admin. (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.

Am. Soc. of Heating, Refrigeration & Air Cond. Engineers (ASHRAE) –

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

American Gas Association –

Indoor air (leakage at a heat register) – 15 pm