Photograph of a Drager hand pump used to measure carbon dioxide levels in the environment. Exposure Limits for Carbon Dioxide Gas - CO2 Limits

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Carbon Dioxide Exposure:

This document discusses the exposure limits for carbon dioxide gas (CO2). We give references and explanation regarding Toxicity of Carbon Dioxide, based on literature search and search on Compuserve's Safety Forum by Dan Friedman. This is background information, obtained from expert sources.

This text may assist readers in understanding these topics. However it should by no means be considered complete nor authoritative. Seek prompt advice from your doctor or health/safety experts if you have any reason to be concerned about exposure to toxic gases.

Links on this page also direct the reader to carbon monoxide gas information in a separate document. IF YOU SUSPECT ANY BUILDING GAS-RELATED POISONING GO INTO FRESH AIR IMMEDIATELY and get others out of the building, then call your fire department or emergency services for help.

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What are the Allowable Limits of CO2 EXPOSURE - Carbon dioxide exposure limits PEL and TLV set by OSHA and NIOSH

Carbon dioxide is regulated for diverse purposes but not as a toxic substance. The table below summarizes

  • The U.S. EPA CO2 exposure limits: The U.S. EPA recommends a maximum concentration of Carbon dioxide CO2 of 1000 ppm (0.1%) for continuous exposure.
  • ASHRAE standard 62-1989 recommends an indoor air ventilation standard of 20 cfm per person of outdoor air or a CO2 level which is below 1000ppm.
  • NIOSH CO2 exposure limits: NIOSH recommends a maximum concentration of carbon dioxide of 10,000 ppm or 1% (for the workplace, for a 10-hr work shift with a ceiling of 3.0% or 30,000 ppm for any 10-minute period). These are the highest threshold limit value (TLV) and permissible exposure limit (PEL) assigned to any material.
  • OSHA CO2 exposure limits: OSHA recommends a lowest oxygen concentration of 19.5% in the work place for a full work-shift exposure. As we calculated above, for the indoor workplace oxygen level to reach 19.5% (down from its normal 20.9% oxygen level in outdoor air) by displacement of oxygen by CO2, that is, to reduce the oxygen level by about 6% (1.4 absolute percentage points divided by 20.9% starting point = 0.06), the CO2 or carbon dioxide level would have to increase to about 1.4% 14,000 ppm.
  • ACGIH exposure limit recommendations for Carbon Dioxide are as follows:
    • CO2 TLV-TWA, 5,000 ppm (9000 mg/m3)
    • CO2 TLV-STEL, 30,000 ppm (54,000 mg/m3)
    • Quoting:
      A TLV-TWA of 5000 ppm (9000 mg/m3) and a TLV-STEL of 30,000 ppm (54,000 mg/m3) are recommended for occupational exposure to carbon dioxide. The recommended values are intended to minimize the potential for asphyxiation and undue metabolic stress. The TLV-STEL is based on the short term, high carbon dioxide exposure studies that produced increased pulmonary ventilation rates. Sufficient data were not available to recommend Skin, SEN, or carcinogenicity notations. [1]

In summary, OSHA, NIOSH, and ACGIH occupational exposure standards are 0.5% CO2 (5,000 ppm) averaged over a 40 hour week, 0.3% (30,000 ppm) average for a short-term (15 minute) exposure [we discuss and define "short term exposure limits" STEL below], and 4% (40,000 ppm) as the maximum instantaneous limit considered immediately dangerous to life and health. All three of these exposure limit conditions must be satisfied, always and together.

What laws regulate carbon dioxide exposure levels?

Of the several industrial hygiene standards-setting groups in this country, the most important and/or most quoted are the National Institute for Occupational Safety and Health (NIOSH), the Occupational Safety and Health Administration (OSHA), and the American Conference of Governmental Industrial Hygienists (ACGIH) but these are recommended standards, not laws.

Standards promulgated by OSHA (called Permissible Exposure Limits or PELs) have the force of law. The other standards are advisory. However OSHA claims the power to force compliance with NIOSH "Recommended Standards" if it chooses to do so. (The main advantage of ACGIH Threshold Limit Values (TLVs) is that they are reviewed and updated annually; neither NIOSH nor OSHA updates its standards with any regular frequency.)

NIOSH limits on Carbon Dioxide Exposure: NIOSH's recommended CO2 exposure limit for 15 minutes is 3 percent. A CO2 level of 4 percent is designated by NIOSH as immediately dangerous to life or health.

OSHA limits on Carbon Dioxide Exposure: The U.S. Department of Labor Occupational Safety & Health Administration, OSHA, has set Permissible Exposure Limits for Carbon Dioxide in workplace atmospheres at 10,000 ppm of CO2 measured as a Time Weighted Average (TWA) level of exposure and OSHA has set 30,000 ppm of CO2 as a Short-Term Exposure Limit (STEL). OSHA has also set a Transitional Limit of 5,000 ppm CO2 exposure TWA. [OSHA's former limit for carbon dioxide was 5000 ppm as an 8-hour TWA.]

Definitions of Short Term Exposure Limits or STEL

What is the definition of "short term exposure" or "Short-Term Exposure Limit (STEL)"? The ACGIH has defined STEL as the concentration (in this case of a gas in air) to which workers can be exposed continuously for a short period of time without suffering from irritation, chronic or irreversible tissue damage, or narcosis of sufficient degree to increase the likelihood of accidental injury, impair self-rescue or materially reduce work efficiency.

What is a "short period"? and what is "short term exposure"?: The definition of "short period" is provided indirectly by ACGIH:

  1. If during an 8-hour work shift (and before it has ended) a worker is exposed to a substance in excess of the threshold limit value, time weighted average exposure permitted exposure level for the entire shift, then that exposure has exceeded the short term exposure limit or STEL.
  2. If a worker is exposed to more than four STEL periods during the course of an 8-hour work shift, with less than 60 minutes between those exposure periods, then also that exposure has exceeded the STEL.

History of Threshold Limit Values TLVs for Carbon Dioxide Exposure Limits [1]

Historical TLVs for CO2 [In the U.S.]

Year Measure Limit
1946-1947 MAC-TWA 5000 ppm
1948-present TLV-TWA 5000 ppm
1976-1985 TLV-STEL 15,000 ppm
1984 proposed TLV-STEL 30,000 ppm
1985-present TLV-STEL 30,000 ppm - i.e. 3.0% concentration of CO2


Source: ACGIH recommendations for CO2 .pdf [1][1b]

Dangerous Levels of CO2 Encountered Outdoors?

Reader Question: 11/25/2014 Rox said:

What is a dangerous level of CO2 outdoors ? I know that we are at about 300-400ppm, at what point it is too dangerous to go outside because of the level on CO2 ?



At our home page for Carbon Dioxide information (CO2 ) you'll find text on the toxicity of this gas.


including comparing indoor with outdoor carbon dioxide levels. It would be unlikely for you to encounter toxic levels of CO2 outdoors unless the outdoor area were somehow enclosed on all sides, in still air and was receiving a source of high-concentration of carbon dioxide gas or unless the area is one exposed to high levels of combustion such as Naeher (2000). In Naeher's research CO2 served principally as an easy-to-measure indicator of other more problematic air quality problems such as high levels of particulates associated with open fires, wood burning stoves, and in some cases gas stoves. In other words, you'd be standing in a smoky area.

The outdoor level of carbon dioxide is relatively constant with occasional peaks

You will find that most research on hazards of gases in outdoor air address carbon monoxide (CO) not carbon dioxide (CO2) - see Curtis (2006) or Thompson (1973).

Outdoor Air Quality and Carbon Dioxide CO2 Levels

Some interesting research that addresses you outdoor air quality question includes the following authors who discuss indoor and outdoor CO2 levels.

  • Baek, Sung-Ok, Yoon-Shin Kim, and Roger Perry. "Indoor air quality in homes, offices and restaurants in Korean urban areas—indoor/outdoor relationships." Atmospheric Environment 31, no. 4 (1997): 529-544.
  • Bobak, Martin. "Outdoor air pollution, low birth weight, and prematurity." Environmental health perspectives 108, no. 2 (2000): 173.
  • Curtis, Luke, William Rea, Patricia Smith-Willis, Ervin Fenyves, and Yaqin Pan. "Adverse health effects of outdoor air pollutants." Environment International 32, no. 6 (2006): 815-830. - Abstract:

    Much research on the health effects of outdoor air pollution has been published in the last decade. The goal of this review is to concisely summarize a wide range of the recent research on health effects of many types of outdoor air pollution. A review of the health effects of major outdoor air pollutants including particulates, carbon monoxide, sulfur and nitrogen oxides, acid gases, metals, volatile organics, solvents, pesticides, radiation and bioaerosols is presented.

    Numerous studies have linked atmospheric pollutants to many types of health problems of many body systems including the respiratory, cardiovascular, immunological, hematological, neurological and reproductive/ developmental systems. Some studies have found increases in respiratory and cardiovascular problems at outdoor pollutant levels well below standards set by such agencies as the US EPA and WHO.

    Air pollution is associated with large increases in medical expenses, morbidity and is estimated to cause about 800,000 annual premature deaths worldwide [Cohen, A.J., Ross Alexander, H., Ostro, B., Pandey, K.D., Kryzanowski, M., Kunzail, N., et al., 2005. The global burden of disease due to outdoor air pollution. J Toxicol Environ Health A. 68: 1–7.]. Further research on the health effects of air pollution and air pollutant abatement methods should be very helpful to physicians, public health officials, industrialists, politicians and the general public.
  • Lee, S. C., and M. Chang. "Indoor and outdoor air quality investigation at schools in Hong Kong." Chemosphere 41, no. 1 (2000): 109-113.
  • Maheswaran, Ravi, Robert P. Haining, Paul Brindley, Jane Law, Tim Pearson, Peter R. Fryers, Stephen Wise, and Michael J. Campbell. "Outdoor Air Pollution and Stroke in Sheffield, United Kingdom A Small-Area Level Geographical Study." Stroke 36, no. 2 (2005): 239-243.
  • Menzies, Richard, Robyn Tamblyn, Jean-Pierre Farant, James Hanley, Fatima Nunes, and Robert Tamblyn. "The effect of varying levels of outdoor-air supply on the symptoms of sick building syndrome." New England Journal of Medicine 328, no. 12 (1993): 821-827.
  • Naeher, L. P., B. P. Leaderer, and K. R. Smith. "Particulate matter and carbon monoxide in highland Guatemala: indoor and outdoor levels from traditional and improved wood stoves and gas stoves." Indoor air 10, no. 3 (2000): 200-205.
  • Ott, Wayne R., and John W. Roberts. "Everyday exposure to toxic pollutants." Scientific American 278, no. 2 (1998): 72-7.
  • REFERENCES at the end of this document contain a more-extensive citation list addressing cargon dioxide and other gases
  • Thompson, C. Ray, Earl G. Hensel, and Gerrit Kats. "Outdoor-indoor levels of six air pollutants." Journal of the Air Pollution Control Association 23, no. 10 (1973): 881-886.


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