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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:
History of Threshold Limit Values TLVs for Carbon Dioxide Exposure Limits 
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Frequently Asked Questions (FAQs) about the allowable exposure limits for elevated levels of CO2 - carbon dioxide
Question: OSHA CO2 exposure limits
I believe that you have interchanged 1.4% and 6% under OSHA above. This is very important as it means that an oxygen analyser will not alarm a dangerous concentration of CO2 . - Mark Crittendon 7/20/2012
Thanks for looking closely at our CO2 exposure limit data, Mark.
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.
"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"
The TWA or TLV is 0.5%,
but the STEL is 0.3%;
the STEL would be a higher level than the TWA or TLV.
John, in a typo there was a 3,000 that should have been 30,000. The ACGIH and other sources' recommended CO2 TLV-STEL is 30,000 ppm (54,000 mg/m3)
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