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

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.


Continue reading at CO2 HEALTH EFFECTS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

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Carbon Dioxide Articles

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