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Allowable Exposure Levels to Carbon Monoxide

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

MI 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 Society of Heating, Refrigeration & Air Conditioning Engineers (ASHRAE) –

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

American Gas Association –

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


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.

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Crowther's HVAC did a total install for an older house for me 14 years ago. They are very good at what they do and are also the epitome of customer service. Any problems that I have had they took care of immediately at very reasonable prices. Add in that they are all really good people and you have the formula for a very successful business. Rereccomend them highly."

Harry Haynie

I selected Crowther to replace both of my HVAC systems and they did a great job. They went the extra mile to correct duct work, and add a vent in order to bring my homes HVAC systems up to the best performance.

Blake Auchmoody

We had a total duel system heat pump replacement. It was a pleasure working with CHAC. From the sales rep to the technicians responsible for the install. Very professional in their craftsmanship and ensuring everything was installed and working correctly. Very courteous and respectful of our property. We are new to the area and am glad we chose CHAC for our HVAC needs.

Steve Casey

For 25 years, Crowther has provided excellent customer service and support for our Carrier zoned heat pump. They are responsive, helpful and great to work with! We love their seasonal maintenance program and have had them complete some system redesign for our home renovation. All around a great team!

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