Synonyms: CO; Carbon oxide; Exhaust gas; Flue gas

OSHA IMIS Code Number: C730

IMIS Name History: Carboxyhemoglobin prior to 5/20/05

Chemical Abstracts Service (CAS) Registry Number: 630-08-0

NIOSH Registry of Toxic Effects of Chemical Substances (RTECS) Identification Number: FG3500000

Department of Transportation Regulation Number (49 CFR 172.101) and 2012 Emergency Response Guidebook [4 MB PDF, 392 pages]: 1016 119; 9202 168 (cryogenic liquid)

NIOSH Pocket Guide to Chemical Hazards - Carbon Monoxide: Physical description, chemical properties, potentially hazardous incompatibilities, and more

National Toxicology Program (NTP) carcinogenic classification: Not listed

International Agency for Research on Cancer (IARC) carcinogenic classification: Not listed

U.S. Environmental Protection Agency (EPA) carcinogenic classification: Not listed

EPA Inhalation Reference Concentration (RfC): Not established

Agency for Toxic Substances and Disease Registry (ATSDR) Inhalation Minimal Risk Level (MRL): Not established

NIOSH Immediately Dangerous to Life or Health (IDLH) concentration: 1,200 ppm

Notes on Other Potential Health Effects and Hazards

1. Chronic occupational exposure to low levels of carbon monoxide may have adverse cardiovascular effects (Sari et al. 2008).
2. Acute exposure to carbon monoxide can cause delayed neurological effects, with an onset of one to four weeks after exposure. Effects include inappropriate euphoria, impaired judgment, poor concentration, memory loss, cognitive and personality changes, and psychosis (ATSDR 2012).
3. EPA (2010) concluded that the clearest evidence for health effects associated with short-term exposure to CO is provided by studies of cardiovascular morbidity. The combined health effects evidence supports a likely causal relationship for this outcome. Controlled human exposure studies provide strong evidence of independent effects of CO on cardiac function, with effects being observed in patients with coronary artery disease following short-term CO exposures resulting in 2.0-2.4% COHb. Suggestive relationships were found for central nervous system effects, reproductive and developmental effects, and respiratory outcomes.

Date Last Revised: 9/6/2012

Literature Basis

• ACGIH: Documentation of the Threshold Limit Values (TLVs) and Biological Exposure Indices (BEIs) - Carbon Monoxide. 2001.
• ATSDR: Toxicological profile for carbon monoxide. June 2012.
• EPA: Integrated Science Assessment for Carbon Monoxide (Final Report). U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-09/019F. January 29, 2010.
• NIOSH: Criteria Document for a Recommended Standard - Occupational Exposure to Carbon Monoxide. 1972.
• NIOSH: Occupational Health Guideline for Chemical Hazards - Carbon Monoxide. September 1978.
• Sari I, Zengin S, Ozer O, Davutoglu V, Yildirim C, Aksoy M: Chronic carbon monoxide exposure increases electrocardiographic P-wave and QT dispersion. Inhal Toxicol. 20(9):879-84, July 2008.

• Calculation Performed and Peer-Reviewed by Trained SLTC Staff:
  method reference: Carbon monoxide (CO) exposure is determined by calculation based on carboxyhemoglobin (COHb) measurements provided by medical professionals as described below. OSHA uses a modified Coburn, Forster, Kane (CFK) Calculation. The documented SLTC modifications (printed in the supplemental report that accompanies the results) use a more accurate version of the CFK equation than the closed-form [e.g., ppm CO = f(x,y,z,…)] version used in the 1972 NIOSH criteria document for the purpose of calculating the 8-hr TWA ppm REL that would result in a 5% COHb level [U.S. Department of Health, Education, and Welfare: Criteria for a Recommended Standard - Occupational Exposure to Carbon Monoxide. Pub. No. HSM 73-11000. NIOSH, Cincinnati, OH (1972).] Poisoning cases generally involve levels above 5% COHb. The more accurate version is necessary to address the full range of % COHb levels found in poisoning cases and requires an iterative computer program. Additional refinements to the calculation address, gender, CO washout after exposure, oxygen administration, the effect of first and second-hand tobacco smoke, elevation, finer gradations of activity levels, and body size. The calculation also provides an incident-specific sampling and analytical error (SAE) based on a Monte-Carlo approach designed to deal with the uncertainties in the data. The calculation is performed at SLTC and the results are critically assessed for correctness by SLTC experts prior to reporting. SLTC experts are available to assist the CSHO in acquiring the data and in interpreting the results.
  method classification: Validated
  blood-gas device: COHb analysis is a routine measurement during the medical response to a suspected CO-poisoning incident or from an autopsy after a suspected CO-poisoning incident. As a result, the COHb analysis is performed using a blood-gas instrument that is part of a quality system. The COHb analysis is not performed at SLTC.
  manufacturer: Varies
  model/type: Varies
  sampling information: The exposure incident is documented on a worksheet. Personal information is used to assess the affect of any tobacco smoking behavior (before, during and after the exposure), blood volume, and activity levels (during and after the exposure). A worksheet is REQUIRED and is available on OSHA's Intranet or by calling SLTC's Physical Measurements Team Leader for instructions.
  The CSHO may supplement the worksheet with additional information such as the results from the emergency responder's or CSHO's area sampling of the worksite.
  post-exposure delay to sampling: Preferably less than about 6 hours for living persons, longer delays may result in significantly higher SAEs or the inability to distinguish an overexposure from the baseline for the individual.
  upper measurement limit: 200,000 ppm
  detection limit: Dependent on details of exposure incident
  sampling and analytical error: Dependent on details of exposure incident

• triage: Contact SLTC's Physical Measurements Team Leader in cases where CO poisoning affects more than 4 individuals. The most practical use of resources sometimes requires evaluating the most severely affected employees.

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