CO2 Toxicity
Home Up


CO2 Toxicity (Carbon Dioxide).

Most of the information on this page was copied from pages located at  ... good job!


Please realize that the Author is not assuming that those levels (for instance of 600 ppm that could offen occur inside a house), are not the level in the open air "for life", from the day you were born to that day when you die.

What are typical Carbon Dioxide levels in air?

bulletCarbon dioxide CO2 levels outdoors near ground level are typically 300 ppm to 400 ppm or 0.03% to 0.040% in concentration.
bulletCarbon 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.
bulletCarbon dioxide CO2 levels indoors in an inadequately vented space with heavy occupation is often measured around 1000 ppm or 0.10% in concentration.
bulletCarbon 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.

What are the HEALTH EFFECTS of CO2 Exposure?

Potential Health Hazards of Toxic Gas Exposure

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.

 The photo shows a Drager colorimetric gas detection tube used to test the CO2 levels in air. In an indoor air test (in our laboratory) the detector found that the CO2 level was about 600ppm which is typical of indoor air and is an acceptable and safe level.

Photograph of a Drager hand pump used to measure carbon dioxide levels in the environment.

Basic Information about Concentrations of CO2 in Air

bullet1,000,000 ppm of a gas = 100 % concentration of the gas. Therefore, 10,000 ppm of a gas in air is a 1% concentration.
bulletAt 1% concentration of carbon dioxide CO2 (10,000 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.
bulletThe concentration of carbon dioxide must be over 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.
bulletAbove 2%, carbon dioxide may cause a feeling of heaviness in the chest and/or more frequent and deeper respirations.
bulletIf exposure continues at that level for several hours, minimal "acidosis" (an acid condition of the blood) may occur but more frequently is absent.
bulletBreathing rate doubles at 3% (30,000 ppm)CO2 and is four times the normal rate at 5% (50,000 ppm)CO2.
bulletToxic 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.

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.

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.

bulletThe U.S. EPA CO2 exposure limits: The U.S. EPA recommends a maximum concentration of Carbon dioxide CO2 of 1,000 ppm (0.1%) for continuous exposure.
bulletASHRAE standard 62-1989 recommends an indoor air ventilation standard of 20 cfm per person of outdoor air, or a CO2 level which is below 1,000ppm.
bulletNIOSH 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.  NIOSH's recommended CO2 exposure limit for 15 minutes is 3.0% or 30,000 ppm . A CO2 level of 4% (40,000 ppm)  is designated by NIOSH as immediately dangerous to life or health.
bulletOSHA CO2 exposure limits: The U.S. Department of Labor Occupational Safety & Health Administration, OSHA, has set Permissible Exposure Limits for Carbon Dioxide in workplace atmospheres at...
bullet 10,000 ppm of CO2 measured as a Time Weighted Average (TWA) level of exposure
bulletOSHA has set 30,000 ppm of CO2 as a Short-Term Exposure Limit (STEL).
bulletOSHA has also set a Transitional Limit of 5,000 ppm CO2 exposure TWA.
bullet[OSHA's former limit for carbon dioxide was 5000 ppm as an 8-hour TWA.]
bulletOSHA 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.

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.)

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.
New Address: Stuart, FL 34997

"LEGACY WEBSITE": Will remain unaltered for foreseeable future.

Phn: (772) 324-1123  Fax:(561) 210-1370,  Email: