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• Toxicity of carbon dioxide gas, CO2 exposure limits
• Symptoms of CO2 or carbon dioxide poisoning
• Health effects of carbon dioxide gas exposure
• Recommendations for gas measurement instruments, gas detector tubes, Draeger & Gastec tubes & pumps for detection of gases

This document discusses the toxicity and exposure limits for exposure to 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. © Copyright 2008 Daniel Friedman, All Rights Reserved. Information Accuracy & Bias Pledge is at below-left. Use the links at page left to navigate this document or to go to Other Website Topics. Green links at left show where you are in our document & website.

• At 1% concentration of carbon dioxide CO₂ (10,000 parts per million or ppm) and under continuous exposure at that level, such as in an auditorium filled with occupants and poor fresh air ventilation, some occupants are likely to feel drowsy.
• The concentration of carbon dioxide must be over about 2% (20,000 ppm) before most people are aware of its presence unless the odor of an associated material (auto exhaust or fermenting yeast, for instance) is present at lower concentrations.
• Above 2%, carbon dioxide may cause a feeling of heaviness in the chest and/or more frequent and deeper respirations.
• If exposure continues at that level for several hours, minimal "acidosis" (an acid condition of the blood) may occur but more frequently is absent.
• Breathing rate doubles at 3% CO₂ and is four times the normal rate at 5% CO₂.
• Toxic levels of carbon dioxide: at levels above 5%, concentration CO₂ is directly toxic. [At lower levels we may be seeing effects of a reduction in the relative amount of oxygen rather than direct toxicity of CO₂.]

Symptoms of high or prolonged exposure to carbon dioxide include headache, increased heart rate, dizziness, fatigue, rapid breathing, visual and hearing dysfunctions. Exposure to higher levels may cause unconsciousness or death within minutes of exposure.

Distinguishing between high carbon dioxide levels CO₂ and low oxygen levels O₂ in air

What may be unclear in some cases is whether the sub-acute (sub-toxic) effects at modestly-elevated levels of CO₂ in air stem from more from exposure to higher levels of carbon dioxide or whether they are due to reduced levels of oxygen. In an enclosed space such as a tight home or an enclosed basement or work space, increasing the level of CO₂ is likely to simultaneously reduce the proportion of Oxygen (O₂) in that same breathing air.

Some experts opine that a complaints that seem to be associated with high CO₂ problem in many if not most circumstances are likely to be actually due to the corresponding reduction in available oxygen in air rather than high toxicity levels of CO₂ in the air. As carbon dioxide levels climb above a few percent the relative proportions of gases making up that air change: the concentration of oxygen in the air inhaled is reduced as the amount of CO₂ is increased.

More carbon dioxide may mean less oxygen: Let's say, sake of simplicity, that we're converting oxygen to carbon dioxide in an enclosed space. Then when the CO₂ level has increased from its normal amount in air (about 0.03%) up to a higher concentration in air of 1.4% CO₂ the concentration of oxygen in air will have decreased from 20.9 to 19.5%. Reducing the oxygen concentration from 20.9% down to 19.5% is equal to a 6.7% reduction in the oxygen level. -- Thanks to thanks to Dr. Roy Jensen for assistance with these details.

What are the effects on humans (and other animals) of reduction of the oxygen levels in air? At sea level, breathing air in which the O₂ level has fallen to 16% percent is equivalent to being at the top of a 9,200-foot mountain - close to the level at which many people will experience shortness of breath while walking. 12% Oxygen in air at sea level corresponds to breathing normal air at an elevation of about 17,400 feet.

CO₂ HEALTH EFFECTS - Potential Health Hazards of Toxic Gas Exposure

Hazard evaluation consists of comparing measurements of exposure (or dose) with exposures (doses) known to be safe or known to be hazardous. For the most part, because of biological variation, "no effect" levels are much easier to estimate than are "first effect" or other levels indicative of injury.

Toxic levels of carbon dioxide: According to occupational exposure and controlled atmosphere research into CO₂ toxicology, CO₂ is hazardous via direct toxicity at levels above 5%, concentrations not encountered in nature [except perhaps at or near an active volcano or at water-logged soils]. At these high levels there is risk of death from carbon dioxide poisoning. At lower levels there may health effects and there certainly are complaints of exposure at lower levels.

In the preceding section of this article, at CO₂ POISONING SYMPTOMS we discussed symptoms of carbon dioxide exposure. On specific individuals, the effects of exposure to elevated levels of carbon dioxide (CO₂) vary by individual and with exposure level, and exposure duration, ranging from drowsiness (perhaps at levels over 1000 ppm continuous exposure) to the toxic effects listed just above.

How might CO₂ accumulate at a dangerous level in a residential property?

Carbon dioxide, CO₂, from a small leak is unlikely to be dangerous, as it can be expected to be diluted with fresh air mixing in a building. But there can be exceptions in which carbon dioxide may accumulate and reach higher, even dangerous concentrations indoors.

• Flue gas spillage: in an enclosed gas-fired boiler room with a deficient chimney draft can produce high levels of CO₂. In a case in which there is sufficient combustion air, say from a direct air duct to the gas burner, the system may not be producing more dangerous carbon monoxide (CO), but the heating system may nonetheless spilling flue gases with a high level of CO₂ into the room from a defective chimney. Since CO₂ being more dense than air it may accumulate in an enclosed basement, crawl space, or boiler room. Alternatively, because the CO₂ in this case is a heating system exhaust, it may be warmer than surrounding air and it may rise upwards in the building into the living space. For this reason when we measure for the presence of flue gases, even if the gas is one which is "supposed to be" heavier than air, we may measure both high and low in the test area.
• Soil sources of high carbon dioxide in buildings: NIOSH reports on an investigation of complaints by homeowners of blurred vision, breathlessness, and "episodic mild confusion" caused by exposure to from elevated carbon dioxide levels in a finished basement and an adjacent crawlspace. West Virginia Department of Environmental Protection detected carbon dioxide levels up to 9.5 percent in the basement and CO₂levels up to 11 percent in the crawlspace grave, with 12 percent in the basement floor drain (suggesting a soil source of CO₂ in a home in West Virginia home, according to a NIOSH report. CO₂ levels in the soil surrounding the home were measured at levels up to 8 percent. The probable source of the high CO₂ levels in the soils under and around this home were probably due to [coal] mining activities.

Are the effects of breathing CO₂ permanent?

Any detrimental effects of low-level CO₂ exposure are reversible, including the long-term metabolic compensation required by chronic exposure to 3% CO₂. -- "A Review of Human Health and Ecological Risks due to CO₂ Exposure," American Geophysical Union, Spring Meeting 2001, abstract #H31C-13, Hepple, R. P.; Benson, S. M., 05/2001.

More Reading:
"Gases: Toxic gases, indoor exposure levels, testing, identification" additional information on gas exposure detection, toxicity, and remedy for a wide range of toxic and other gases.

CO₂ EXPOSURE LIMITS - 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 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%, 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, 3% (3,000 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.

What are the component gases that make up normal air and in what proportions or percentages do they ocur?

At sea level on earth, what is the composition of the air we breathe? That is, what gases make up normal outdoor air? How much CO₂ is in air? How much oxygen is in air? and how much nitrogen is in the earth's atmosphere? Here is the mix of gases in normal outdoor air. The earth's atmosphere (measured close to ground level) is made up of 78.1% nitrogen, 20.9% oxygen, 0.9% argon, 0.03% carbon dioxide, and 0.04% other gases. Let's look at some typical CO₂ levels in both percentage and expressed in parts per million, which is how most instruments measure gas concentrations. [The mix of gases in air near some manufacturing facilities or in some cities may be a bit different.]

What are typical Carbon Dioxide levels in air?

• Carbon dioxide CO₂ levels outdoors near ground level are typically 300 ppm to 350 ppm or 0.03% to 0.035% in concentration.
• Carbon dioxide CO₂ levels indoors in occupied buildings are typically around 600 ppm to 800 ppm or 0.06% to 0.08% in concentration. You'll find this data in many indoor air quality articles and books and it's consistent with what we find typically in our own field measurements.
• Carbon dioxide CO₂ levels indoors in an inadequately vented space with heavy occupation is often measured around 1000 ppm or 0.10% in concentration. I have measured levels around 1200 ppm in occupied basement offices in a hospital where the staff worked in an area which had no decent fresh air intake into their ventilation system. In 1989 I also measured 1200 ppm at chest height in the center of the sanctuary in a Jewish synagogue during the high holy days in a small New York city. I also observed people nodding off. We were never sure if it was a droning sermon, exhausted worshipers at the end of a long week, or the CO₂ level. But there was no doubt that we were not meeting recommended ventilation standards for that space.
• Carbon dioxide levels above 1500 to 2000 ppm are likely to be reached only in unusual circumstances (being enclosed in an airtight closet for a long time) or in industrial workplace settings such as we cited above.

Oxygen gas level measurements & poisoning symptoms: If you reached this paragraph by scrolling down, read about

Carbon Monoxide Gas Level Measurements & Poisoning Symptoms: If you reached this paragraph by scrolling down, read about CARBON MONOXIDE - CO hazards, detection, exposure limits, and health effects by using the links at the left on these pages.

Technical Reviewers

Particular thanks are due to experts and also consumers who read these articles and suggest corrections, changes, and additions to the material. Content suggestions, technical corrections and content critique are invited for any of the content at our website.

• Daniel Friedman - principal author
• 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 this calculation.
• Technical reviewers are invited to comment or ask questions - contact us

More Information on Toxic Gas Detection, Exposure, Test Procedures, Toxicity, and Remedy, & Building Diagnostic Inspections and Repairs

Toxic Gas Exposure Hazards and Test Protocols including links to our toxic gas exposure screening and gas testing protocols.

Gases: Toxic gases, indoor exposure levels, testing, identification

• 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
• Gas Exposure Hazard Levels: for Toxic Gas Exposure to Ammonia, Arsine, Arsenic, Bromine, Carbon Dioxide, Carbon Monoxide, Hydride, Ozone - allowable exposure levels and hazard levels
• Carbon Dioxide Gas Toxicity hazard level, poisoning symptoms, & testing
• Carbon Monoxide Gas Toxicity hazard levels, poisoning symptoms, & testing
• 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.
• 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

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