Carbon Monoxide Headquarters



Allowable (Legal) Limits for CO (cont.):



American National Standards Institute (ANSI Z21.1) -

Max. CO conc. allowed from an unvented space heater ("air-free") - 200 ppm

Max. CO conc. allowed in a furnace flue gas ("air-free") - 400 ppm

Max. CO conc. allowed for emissions from an unvented gas oven ("air-free") - 800 ppm


"air-free" refers to the concentration of CO in combustion gases undiluted with flue, or other gases containing little CO. "air-free" values may be computed using a equation that takes into account the O2 concentration of the flue gas.





American Conference of Governmental Industrial Hygienists, Inc.: The history of Threshold Limit Values (TLV) from this group has been to continually lower the values as more information about the effects of CO on humans has become available. The current intent is to keep COHb below 3.5%, since many deleterious neurobehavioral effects have been reported above this COHb level.

1946 - 1947: MAC-TWA = 100 ppm
1946 - 1966: TLV-TWA = 100 ppm
1965: TLV-TWA = 50 ppm (proposed)
1967: TLV-TWA = 50 ppm
1976: TLV-STEL = 400 ppm
1991: TLV-TWA = 25 ppm (proposed)
present TLV-TWA = 25 ppm


Other Nations:

Australia: TWA = 50 ppm, STEL = 400 ppm
Fed. Republic of Germany: TWA = 30 ppm, 60 ppm for 30 minutes.
Sweden: TWA = 35 ppm, 100 ppm for 15 minutes.
United Kingdom: TWA = 50 ppm, STEL = 300 ppm (10 minutes)


...... Last changed 08/23/00



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