Photograph of a Drager hand pump used to measure carbon dioxide levels in the environment. Health Effects of Exposure to High levels of of Carbon Dioxide Gas Exposure, CO2

  • CO2 HEALTH EFFECTS - CONTENTS: Health effects of chronic or high exposure to carbon dioxide gas. What are normal levels of carbon dioxide outdoors & in buildings; what are the effects of exposure to various concentraion levels of CO2 ?  
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Health effects of high-level CO2 exposure:

This document discusses the health effects of exposure to elevated levels of 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.

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What are the HEALTH EFFECTS of CO2 Exposure?

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.

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.

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.

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.

Ongoing Research on the Effects of Increased CO2 Exposure

Discussion with Esther Cook, a scientist researching the effects of low-level CO2 exposure. [Edited by Daniel Friedman].

I am a scientist interested in the effects of increased CO2 . We know that plants grow more luxuriantly, and that this must ultimately support more animal life. I have done a PubMed and Academic search and can find almost no studies. I did find a claim that burrowing rodents typically have 1 to 4% carbon dioxide in their burrows. I also found research on 7% carbon dioxide on the retinas of baby mice--because this level is deliberately used on human beings--preemie babies to help their lungs develop faster. I am in communication with the Idsos, who are plant experts and CO2 researchers. They can't find much either. So far I have found:

There are hundreds of plant studies, and greenhouses and aquariums routinely enrich with CO2 to enhance growth. But what about ourselves? Might it be the case that the results of [some] CO2 studies are politically incorrect, and that the science is has been suppressed.

There is an optimum CO2 concentration somewhere; it is higher than today's, and the individual human's life is being shortened by the panic on the subject. Of course, there is indeed such a thing as "too much of a good thing," and there are some examples of people who died when too much CO2 was produced in enclosed spaces.

It would be worth while to find out what the optimum CO2 level for humans and other animals actually is. Paleontological records show that about half the time since the Cambrian was spent at a very steady 10 degrees C above current averages.

This would be exactly room temperature, and I do not think that is an accident. Recent posts revealed why the Earth's temperatures would not rise above that point--increasing evaporation from the oceans would prevent any higher temperature, but we would get the conditions described in Genesis about Eden: a mist would water the ground.

Carbon Dioxide Exposure Standards & Effects

Table of Health Effects & Hazards of Carbon dioxide Gas at Various Concentrations & Exposure Durations

CO2 Concentration in Air

Duration of Exposure

Health Effects or Hazards of Breathing CO2 gas at this level [12]

Typical Outdoor Levels of Carbon Dioxide, CO2 levels in outdoor air

0.030 - 0.050% CO2
300 - 500 ppm

Typical outdoor air CO2 levels


Typical outdoor CO2 levels range from 300-500 ppm

Levels At or Below Which People Are Not Likely to Be Aware of the CO2 Concentration

0.060% CO2
600 ppm


None, indoor CO2 levels of an occupied office space may be in this range, [OPINION: check fresh air intake at higher levels]

One source[4] sets 600 ppm as an acceptable level of CO2

700 ppm  

According to ASHRAE indoor CO2 concentrations of about 700 ppm above outdoor CO2 levels in air (that is indoor CO2 over about 1050 ppm) indicate an outdoor air ventilation rate of about 7.5 L/s/person (15 cfm/person) presuming activity levels found in a typical office. At this rate 80% of unadapted people (visitors) won't complain of odors from human bioeffluents.

Quoting: According to ASHRAE indoor CO2 concentrations of about 700 ppm above outdoor CO2 levels in air (that is indoor CO2 over about 1050 ppm) indicate an outdoor air ventilation rate of about 7.5 L/s/person (15 cfm/person) presuming activity levels found in a typical office. At this rate 80% of unadapted people (visitors) won't complain of odors from human bioeffluents.

0.06 - 0.10% CO2
600 - 1000 ppm

Complaints of stiffness

"and odors" per one resource[4] which seems odd since CO2 is odorless.

0.10% CO2
1000 ppm of CO2

OSHA standard.

This is not an ASHRAE standard but is an ASHRAE guideline for comfort acceptability, not a ceiling value for air quality.[5]

0.10% - 0.12% CO2

1,000-1,200 ppm CO2


Hermann (2002) comments that "... 1000 ppm of CO2 [when considered alone] has no real bearing on the building ventilation rate...." He offers a table relating the CO2 level difference between indoor and outdoor air to the building ventilation rate per person.

Indoor vs Outdoor CO2 Level versus Building Ventilation Rate

Approximate CFM / Occupant CO2 Level above Outdoor Air
15 707
20 530
25 424
30 353
Herrmann, Donald C., "Understanding CO2 and ASHRAE 62 [now obs?], A Technical Note", Energy Engineering, Vol. 99, No. 1, 2002, retrieved 25 Nov 14, original source:
0.10% - 0.25% CO2
1000-2500 ppm CO2
  One source[4] reports complaints of general drowsiness at 1000-2500 ppm of CO2
0.5 % CO2
5000 ppm CO2
  5,000 ppm CO2 is the OSHA's maximum 8-hour work period concentration allowed. This level is commonly used by workers' compensation boards in some U.S. jurisdictions.

Effects of Higher Levels of CO2

Less than 2% CO2
Less than 20,000 ppm CO2


  Short-term exposure to CO2 at levels below 2% (20,000 parts per million or ppm) has not been reported to cause harmful effects.

Occupants do not generally express awareness nor symptoms related to the CO2 level.

CO2 Levels at or Above Which Complaints are Likely

2-3% CO2
20,000 - 30,000 ppm
  Occupants become aware of poor indoor air quality, may cause a feeling of heaviness in the chest and/or more frequent and deeper respirations.

Very High CO2 Levels at or Above Which Adverse Health Effects Begin

20,000 - 30,000 ppm
"several hours" Minimal "acidosis" (an acid condition of the blood) may occur but more frequently is absent.
30,000 ppm
  Breathing rate increases to 2x normal
15 hrs/day, 6 days Decreased night vision and colour sensitivity;
3.3 % to 5.4%
15 minutes Increased depth of breathing

Below 5%
Below 50,000 ppm

  Indoor air quality complaints or effects may be due to reduced oxygen level rather than CO2 toxicity

CO2 Levels or Concentrations Posing Serious Health Risks

50,000 ppm of CO2


Breathing rate increases to 4 x normal. Headaches, some impairment.

Over 5%   CO2 levels over 5% or 50,000 ppm are directly toxic
15 minutes At 7.5%, a feeling of an inability to breathe (dyspnea), increased pulse rate, headache, dizziness, sweating, restlessness, disorientation, and visual distortion developed.
6% "several" minutes affects the heart, altered electrocardiograms.
6.5% - 7.5% 20 minutes Twenty-minute exposures to 6.5 or 7.5% decreased mental performance.
6.5% - 7.5% 70 minutes Irritability and discomfort were reported with exposure to 6.5% for approximately 70 minutes.
10% 1 1/2 minutes Eye flickering, excitation and increased muscle activity and twitching.
Over 10%   Difficulty in breathing, impaired hearing, nausea, vomiting, a strangling sensation, sweating, stupor within several minutes and loss of consciousness within 15 minutes.
19.5%   Standard Australian 1st alarm level
Over 20% 1 minute or less Several deaths have been attributed to exposure to concentrations greater than 20%.
30% 20-30 seconds Affects the heart, altered electrocardiograms.
30%   Exposure to 30% has quickly resulted in unconsciousness and convulsions.
"Very high"   Damage to the retina, sensitivity to light (photophobia), abnormal eye movements, constriction of visual fields, and enlargement of blind spots.

Notes to the Table:

1. Adapted & expanded from Health Effects of Carbon Dioxide Gas", CCOHS [12]

2. Effects of CO2 can become more pronounced upon physical exertion, such as heavy work.

3. Higher CO2 concentrations can affect respiratory function and cause excitation followed by depression of the central nervous system. High concentrations of CO2 can displace oxygen in the air, resulting in lower oxygen concentrations for breathing. Therefore, effects of oxygen deficiency may be combined with effects of CO2 toxicity.

4. Engineering Toolbox, retrieved 26 Nov 14 original source

5. Contrary to some sources, this 1,000 ppm CO2 value is not contained in the latest ANSI/ASHRAE 62-1999 standard. See Petty (un-dated) at REFERENCES


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