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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.
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. 
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:
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.
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 
Historical TLVs for CO2 [In the U.S.]
30,000 ppm - i.e. 3.0% concentration of CO2
Source: ACGIH recommendations for CO2 .pdf [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.
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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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.
Referring to the OSHA CO2 exposure limits, I have edited our text above to make the calculation of percentage points more clear: (1.4 absolute percentage points divided by 20.9% starting point = 0.06 - or 6% reduction in the CO2 level)
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.
Thank you for the careful read and the question. We are dedicated to making our information as accurate, complete, useful, and unbiased as possible: we very much welcome critique, questions, or content suggestions for our web articles. InspectAPedia is an independent publisher of building, environmental, and forensic inspection, diagnosis, and repair information for the public - we have no business nor financial connection with any manufacturer or service provider discussed at our website.
"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"
Sorry is this a mistake, or is there something obvious I am missing?
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.
Is the upper limit for continuous 24 hour exposure now 0.1%?
John Brechin 11/13/2012
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)
Question: is a level of CO2 at 50 dangerous?
(Mar 15, 2013) France's said:
My brother has co2 level at 50, is this dangerous?
France's, I'm sorry but I cannot form an confident opinion from your question as I have no idea what measurement was made, where, nor if we're talking about carbon dioxide level in air, in the bloodstream, or elsewhere
According to Medline, "In the body, most of the CO2 is in the form of a substance called bicarbonate (HCO3,). Therefore, the CO2 blood test is really a measure of your blood bicarbonate level."
If that is the measurement you mean, Medline explains that
"The normal range is 23-29 mEq/L (milliequivalent per liter)."
Your brother should ask his doctor for her opinion about the meaning of his tests.
Question: what kind of test is done for septic odors?
(Dec 19, 2012) test said:
What type of text might you recommend to be done in a place that often has septic odors? I fear that even when the odor is not there that the contaminants are left behind.
While sewer gases or septic system odors contain a complex of gases typically people test for methane in air, and where there has been a sewage spill, a test of surfaces is performed for bacteria such as eColi associated with sewage. Sewer gas is not itself a Carbon dioxide issue (the subject of this article where you posted the question) and is discussed separately at a couple of articles you'll want to see:
Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.
 Carbon Dioxide, CAS Number: 124-38-9, TLV-TWA, 5000 ppm (9000 mg/m3), TLV-STEL, 30,000 ppm (54,000 mg/m3), from ACGIH and recommended by reader James Miller, USN Submarines, Ret. 3/20/2013. Copy on file as ACGIH recommendations for CO2 .pdf
[1a] CDC Centers for Disease Control and Prevention, NIOSH Pocket Guide to Chemical Hazards, Carbon Dioxide, http://www.cdc.gov/niosh/npg/npgd0103.html, retrieved 3/20/2013
 Dr. Roy Jensen, Department of Chemistry, Grant MacEwan College, Edmonton, AB for technical review and critique 8/23/07.
Dr. Jensen notes that if we increase the CO2 level in air in an enclosed space from
its normal level of about 0.03% (we counted it as starting at 0) to a level of 1.4%, we obtain a corresponding
decrease in the oxygen level from its normal level (at sea level) of about 20.9% down to 19.5%, for a 6.7%
reduction in the amount of oxygen available. The amount of oxygen lost is 6.7 % (1.4/20.9 * 100 %). Our earlier version of this document was incorrect in
 Thanks to careful reader Michael P. Doukas at USGS for correcting a decimal point error in our numbers on CO2 exposure limits - August 2010.
A Toxic Gas Testing Plan: A Gas Sampling Plan for Residential and Commercial buildings lists some of the toxic indoor gases for which we test, depending on the building complaint and building conditions
GTSP, 2006: Carbon Dioxide Capture and Geologic Storage: A Core Element of a A Global
Energy Technology Strategy to Address Climate Change (PDF, 37 pp., 6.05 MB, About PDF).
April 2006, JJ Dooley et al. Global Energy Technology Strategy Program (GSTP)
IPCC, 2005: Special Report on Carbon Dioxide Capture and Storage, Special Report of the
Intergovernmental Panel on Climate Change [Metz, Bert, Davidson, Ogunlade,
de Coninck, Heleen, Loos, Manuela, and Meyer, Leo (Eds.)]. Cambridge University Press, The
Edinburgh Building Shaftesbury Road, Cambridge CB2 2RU England
Fluorine, Its Compounds, and Air Pollution,: a Bibliography with Abstracts, US Environmental Protection Agency, Office of Air Quality Planning and Standards, Research Triangle Park, North Carolina 27711, December 1976. Web search 08/28/2010, original source: http://nepis.epa.gov.
NOTE: because the EPA's original source of this document in PDF format is damaged we have created a text image file, converted to a new PDF for readability.
Formaldehyde: US EPA. UFFI (Urea Formaldehyde Foam Insulation) was previously considered a hazard (formaldehyde outgassing). Subsequent research virtually closed concern regarding this material; however formaldehyde appears to remain a health concern for sensitive individuals.
Nitrogen Oxides: Air Quality Criteria for Oxides of Nitrogen, Vol III of III, US EPA, EPA600/8-91/049cF, August 1993, web search 08/28/2010, original source: http://nepis.epa.gov [Large PDF 25MB] Key chapters in this document evaluate the latest scientific data on (a) health effects of
NOx measured ill laboratory animals and exposed human populatIOns and (b) effects of NOx
on agricultural crops, forests, and ecosystems, as well as (c) NOx effects on visibility and
nonbiological materials. Other chapters describe the nature, sources, distribution,
measurement, and concentratiOns of NOx m the environment These chapters were prepared
and peer reviwed by experts from various state and Federal government offices, academia,
and private industry for use by EPA to support decision makIng regarding potentIal risks to
public health and the enVIronment Although the document IS not intended to be an
exhaustIve literature reVIew, It IS intended to cover all the pertinent literature through early
Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
Sampling for gases in air such as VOC's, MVOC's, toxic chemicals, and combustion products.
Unfortunately no single test or tool can detect all possible building contaminants. We use methods and equipment which can test for common contaminants. If the identity of a specific contaminant is known in advance we can also test for a very large number of specific contaminant gases in buildings.
We use gas sampling equipment provided by the two most reliable companies in the world, Draeger-Safety's detector-tubes and Drager accuro� bellows pump, the Gastec� cylinder pump and detector-tube system produced by Gastec or Sensidyne, and
we also use Sensidyne's Gilian air pump. For broad screening for combustibles and a number of other
toxic gases and for leak tracing we also use Amprobe's Tif8850. All of these instruments, their applications, and sensitivities (minimum detectable limits) for specific gases are described in our Gas Sampling Plan online document.
Radon Gas U.S. EPA Radon level maps, web search 2005, original source: http://www.epa.gov/iaq/radon/zonemap/zmapp33.htm
"Table Z-1 Limits for Air Contaminants, 1910.1000 Table Z-1" OSHA standard for air contaminant limits (http://www.osha.gov/pls/oshaweb/owadisp.show_document?p_table=STANDARDS&p_id=9992) - includes for CO2 , Carbon dioxide.........| CAS No. 124-38-9 | 5000 ppm | 9000 mg/m3 limits for carbon dioxide as an air contaminant.
GAS EXPOSURE EFFECTS, TOXIC Toxic Gas Exposure Hazards and Test Protocols including links
to our toxic gas exposure screening and gas testing protocols.
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