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Photograph of a Drager hand pump used to measure carbon dioxide levels in the environment.Toxicity of Carbon Dioxide Gas Exposure, CO2 Poisoning Symptoms, Carbon Dioxide Exposure Limits

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Carbon Dioxide CO2 Exposure Limits & Toxicity to humans:

This article series discusses normal and abnormal CO2 gas levels, the toxicity and exposure limits for exposure to carbon dioxide gas (CO2). We discuss Carbon Dioxide gas levels in outdoor air, in buildings, typical CO2 levels and conditions under which levels are unsafe.

We discuss the symptoms of carbon dioxide poisoning, describe different types of risks where high levels of CO2 may be present, and present data about the effects of CO2 exposure. 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.

We give references and explanation regarding toxicity of Carbon Dioxide. Links on this page also direct the reader to carbon monoxide gas information in a separate document.

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Information about Concentrations of Carbon Dioxide - CO2 in Air

Photograph of a Drager hand pump used to measure carbon dioxide levels in the environment.- Daniel Friedman, with special thanks to Per Levéen, Telia Mobile, Sweden [1], Dr. Roy Jensen, (Canada) [2]. and Stephen Fisher, B.Sc., Sales Director, K.D.Fisher & Company, Pty., Ltd., Australia, [3] for technical editing & comments.

Article Series Contents

The Effects of CO2 at Various Levels or Concentrations in Air

Recent research suggests that even at modest elevations of CO2 levels indoors mental acuity and decision making ability may be impaired. In turn that research suggests that improved building fresh-air ventilation beyond contemporary IAQ standards (5-10 cfm of fresh air per person 13 per minute) may not be adequate.

This table describes what happens to a typical occupant's mental and physical health as the concentrations of carbon dioxide increase in the air a person is breathing.

Carbon Dioxide Concentrations vs. Health Effects & IAQ

CO2 ppm CO2 Percent of Air Duration Effects
350 - 400 ppm 0.035% - 0.04% [12]   Typical outdoor CO2 level - 0.3% by volume = 0.23 mmHg
600 0.06% hours reduced mental performance for some [8]
1,000 0.10% hours reduced test scores [7] common in classrooms [9],
1,200 0.12% hours Indoors indicates poor fresh-air ventilation [6],
1,000 - 2000 0.10% - 0.20% hours Occupant complaints of drowsiness, poor indoor air [14]
2,500 0.25% hours Significantly reduced mental performance for some [7]
3,000 0.3% 6+ hrs. Perceived reduced IAQ w/ bioeffluents present [10]
2000 - 5000 0.20% - 0.5% hours Headaches, sleepiness, and stagnant, stale, stuffy air.
Poor concentration, loss of attention, increased heart rate,
slight nausea [14]
5,000 0.5% hours

Reduced mental performance, found in some classrooms [8]

Prior NASA SMAC CO2 limit for long term space voyage (obs)

Toxicity or oxygen deprivation may occur [14]

This is the PEL for daily workplace exposures.

10,000 1% minutes + Drowsiness [1]
12,000 1.2% ? Headache complaints 9 mmHg [12]
20,000 2% min. to hrs. Awareness of poor IAQ [2]
Above 20,000 > 2% min. to hrs. Heaviness in chest, difficulty breathing, possible acidosis after several hours [3]
30,000 3% minutes Breathing rate doubles [4]
40,000 4% minutes Immediately harmful due to oxygen deprivation [14]
50,000 5% minutes Breathing rate 4 x normal, threshold of toxicity [4]
Above 20,000 > 5% minutes Toxic, unconsciousness, death [5]

Notes to the table above

Watch out: 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.

1,000,000 ppm of a gas = 100 % concentration of the gas, and 10,000 ppm of a gas in air = a 1% concentration.

  1. 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.

    At lower CO2 levels we may be seeing effects of a reduction in the relative amount of oxygen rather than direct toxicity of CO2
  2. 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.
  3. Above 2% concentration in air, 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.
  4. Breathing rate doubles at 3% CO2 and is four times the normal rate at 5% 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.
  5. Toxic levels of carbon dioxide: at levels above 5%, concentration CO2 is directly toxic.
  6. Indoor CO2 levels of 1,200 ppm and above indicate poor fresh-air ventilation. Respiratory or IAQ complaints at this indoor CO2 level may be due to increased concentrations of other offgassing products from building materials (formaldehyde) or increased odor levels from various sources.
  7. Some studies suggest worse test scores at CO2 level of 1000, and much worse test score performance at an indoor CO2 level of 2,500 ppm than at 600 ppm (Satish 201, Liu 2017, Allen 2015, )
  8. 600 ppm CO2 concentration levels indoors is common in crowded spaces and may result in reduced mental performance on some tasks for some people (Fisk 2013)
  9. Miller, Sherry ... NYT in process U Colorado
  10. ... moderate concentrations of bioeffluents, but not pure CO2 , will result in deleterious effects on occupants during typical indoor exposures. (Zhang 2015)

    However Liu found that 3000 ppm CO2 did not exacerbate IAQ complaints at elevated temperatures up to 35°C (95°F)(Liu 2017)
  11. NASA's SMAC for CO2 was 5000 but this control was deleted in 2017 (NASA 2017)
  12. (Law 2010 citing (Sliwka 1998))
  13. ASHRAE Standard 6.2.1, Table 6.2.2.1 provides recommended outdoor or "fresh air" ventilation rates expressed in cfm/person or L/s/person as well as rates expressed in cfm/ft2 or l/s-m2 . These rates vary by type of occupancy category. For example break rooms need 5 cfm/person while a media center or science lab needs 10 cfm/person.

    ASHRAE 6.2.1 VENTILATION for ACCEPTABLE INDOOR AIR QUALITY [PDF]
  14. Wisconsin DHS, Health Effects of Carbon Dioxide, Chemical reference number (CAS): 124-38-9 - (2021) - Wisconsin Department of Health Services, 1 West Wilson Street Madison, WI 53703 USA, Tel: 608-266-1865 - retrieved 2022/02/25, original source, https://www.dhs.wisconsin.gov/chemical/carbondioxide.htm
    Excerpt:
    Exposure to CO2 can produce a variety of health effects. These may include headaches, dizziness, restlessness, a tingling or pins or needles feeling, difficulty breathing, sweating, tiredness, increased heart rate, elevated blood pressure, coma, asphyxia, and convulsions. The levels of CO2 in the air and potential health problems are given in the table above, . [Adapted from this and other sources - Ed.]
  15. CARBON DIOXIDE HEALTH EFFECTS [PDF] U.S. EPA, retrieved 2022/07/15 original source: https://www.epa.gov/sites/default/files/2015-06/documents/co2appendixb.pdf
    Excerpt:
    Appendix B presents an overview of the acute health effects associated with carbon dioxide. Part I discusses the dangerous, lethal effects of carbon dioxide at high exposure concentrations. The minimum design concentration of carbon dioxide for a total flooding system is 34 percent (340,000 ppm).

    When used at this design concentration, carbon dioxide is lethal. Part II discusses the potentially beneficial effects of carbon dioxide at low exposure concentrations and the use of added carbon dioxide in specialized flooding systems using inert gases.
  16. CARBON DIOXIDE CO2: GEOLOGIC SEQUESTRATION HEALTH EFFECTS: "VULNERABILITY EVALUATION FRAMEWORK FOR GEOLOGIC SEQUESTRATION OF CARBON DIOXIDE [PDF] (2008) US EPA, EPA430-R-08-009, July 2008, web search August 2010
  17. CARBON DIOXIDE CO2: GEOLOGIC SEQUESTRATION [PDF], U.S EPA, web search 08/28/2010, original source: http://www.epa.gov/climatechange/emissions/co2_gs_tech.html

How to Convert mmHg to ppm concentrations of a gas in air

On Earth, the ambient CO2 concentration is about 0.03% by volume (0.23 mm Hg). (Law 2010)

Watch out: These example calculations converting ppm to mmHg are subject to technical review

Conversion factor for concentration of a gas in air in ppm to concentration in mmHg

mmHg = ppm / 1,304.34

Derivation:

0.03% concentration of CO2 = 300 ppm = 0.23 mmHg (Law 2010)

300 ppm / 0.23 mmHg = 1,304.34

Examples:

5000 ppm / 1,304.34 = 3.8 mmHg

0.5% concentration of CO2 = 5000 ppm CO2 = 3.8 mmHg [ w/o adjustments for temperature, humidity, etc.] - Ed.

To Convert ppm to mmHg

divide ppm by 1,304.34 to get mmHg

or because 1/1,304.34 = 0.007666713 you can also

multiply ppm x 0.00076667 to get mmHg

...

To Convert mmHg to ppm

divide mmHg by 0.00076667 to get ppm

or

multiply mmHg by 1,304.35 to get ppm

Also see Lenntech on converting ppm at https://www.lenntech.com/calculators/ppm/converter-parts-per-million.htm

Also see mmHg(CO2) = mmHg(system) * (reading from sensor in ppm) / 1,000,000 cited at https://forums.parallax.com/discussion/147975/converting-co2-ppm-to-mmhg
Quoting

So if you had standard pressure then the mmHg of "system" would be 760mmHg.

So in this case:

mmHg(CO2) = (reading from sensor in ppm) * 0.000760

Edit: The above will only work if the parts per million is a mole fraction (same as volume fraction in many cases). If the measurement is ppm mass fraction, then you'd need and additional conversion factor.

See also the scientific explanation at Botero, Nick, How to Calculate the PPM From Vapor Pressure (2017), https://sciencing.com/calculate-ppm-vapor-pressure-6457861.html

What are the Typical CO2 Carbon Dioxide Levels Found in Outdoor Air?

Photograph of a Drager hand pump used to measure carbon dioxide levels in the environment.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 considered an acceptable and safe level.

While authorities indicate that CO2 is present in outdoor air at 0.035% [12], (or 0.04% in popular sources - 2021 - Ed.) our own measurements [DF] indicate that at a given locality the actual CO2 level varies according to local conditions including temporal factors such as nearby fossil-fuel engines such as automobiles & buses.

In our measurements outdoors the typical carbon dioxide CO2 level in air typically varies between 300 ppm to 400 ppm.

400 ppm is a 0.04% concentration of a gas in air - slightly higher than the "official" figure.

Comparing Outdoor CO2 Levels with Indoor CO2 in Buildings

When studying carbon dioxide levels inside of a building we therefore start with an outdoor baseline measurement, or several, obtained at varying distances from the structure.

A comparison of the actual outdoor CO2 level with even a relatively low level of indoor CO2 (600 ppm and higher) may indicate a lack of adequate fresh air entering a building.

Carbon dioxide gas level measurements may be used in a study of indoor air quality even when the absolute levels of CO2 itself are not harmful. But as we explain below, at higher levels CO2 itself can affect building occupants and can even become dangerous or fatal.

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 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.

However, the TOXIC effects of elevated levels of CO2 are serious at levels when the oxygen reduction effects are only minor. [3]

CO2 Carbon Dioxide poisoning symptoms

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.

Here we discuss Carbon Dioxide gas levels in outdoor air, in buildings, typical CO2 levels and conditions under which levels are unsafe. We discuss the symptoms of carbon dioxide poisoning, describe different types of risks where high levels of CO2 may be present, and present data about the effects of CO2 exposure.

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.

High CO2 Exposure Case Reports

Case Report Example of Drowsiness Possibly Ascribe to Elevated Levels of Carbon Dioxide (CO2) in Vassar Temple, Poughkeepsie

Drager accuro gas detector for use with colorimetric gas detection tubes described here (C) Daniel Friedman at InspectApedia.com

Ca. 1990 and using the Draeger (Dräger) gas detection tubes and a simple hand pump - shown here, the author [DF] performed a series of carbon dioxide level measurements during religious services at the Vassar Temple, a Reform Jewish Synagogue in Poughkeepsie, New York.

A previous inspection of the building's heating and air conditioning system had revealed that there was no working provision for the introduction of fresh outdoor air or "make-up air" into the buildings's duct system.

Carbon Dioxide levels were measured (discreetly) from a central first floor position in a pew during the Yom Kippur religious services, at ten minute intervals during this high holy day service.

For readers un-familiar with this religious service we include this explanation:

Synagogue is a critical part of Yom Kippur, offering five prayer services. During each one, the congregation confesses its sins collectively. Some attendees wear white clothing or a kittel, a white garment that symbolizes a burial shroud, the clothing of angels, and the purity of forgiveness. - (Blakemore 2021)

Expert sources point out that as the CO2 level in a building exceeds 1000 ppm and approaches 2000 ppm there may be occupant complaints of drowsiness and poor air, and indeed we observed some worshippers appearing to nod off. Or perhaps they were simply contemplating their sins and thinking about starting the new year afresh - with sins forgiven and maybe afresh with better air.

Research

Case Report Example of Fatal Levels of Carbon Dioxide (CO2) in a Building 

This is important because we recently had an accident with CO2 in Sweden killing two persons.

According to the newspapers CO2 is nontoxic and it is the decreased oxygen levels that kills. THIS CONCEPT IS WRONG.

Using the calculation equation above one can quickly conclude that adding 31 litres of CO2 to a 100 litre enclosed space would result in a 23.7% CO2 by volume in air, which would be almost instantly fatal, and 16% oxygen by volume in air, (equivalent to breathing at 2800 meters above sea level, which is dangerous, because it can lead to poor decision making, but not fatal).

It is the toxic properties of CO2 that is fatal, not the drop in oxygen.

In conclusion, in the event of a CO2 Cylinder leak, it is the toxic properties of CO2 that is fatal, long before oxygen levels have been reduced to fatally low levels.

According to the calculation given below, a level of 1.4% CO2 cause a drop of oxygen from 20.9% to 19.5%. As the arithmetic above shows, This calculation is misleading. Saying that adding 1.4% CO2 causes oxygen to drop to 20.9 - 1.4 = 19.5% is like saying that adding 20.9% CO2 would cause oxygen to drop to 20.9 - 20.9 = 0% That is of course not true. The correct and more precise calculation is provided above this paragraph.

Reduced % Oxygen & Other Gases When Carbon Dioxide (CO2) Reaches 5% of room air

Using either of the above calculation methods, the introduction of 5% CO2 to the room's air volume will reduce each of the components of normal air to 95% of their original proportion.

 Component of Air

Standard Air Percentage After Addition of 5% CO2

Nitrogen (N2)

78.0% 74.1%

Oxygen (O2)

20.9% 19.85%

Argon (Ar)

1.0% 0.95%

Carbon Dioxide (CO2)

0.04% 5.04%

Notes to the table above

Jensen [2] at REFERENCES 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.

A 5% level of CO2 is directly toxic, yet as can be seen, the Oxygen level is at 19.85%, whereas the standard Australian 1st alarm level is set at 19.5%, so an oxygen sensor would not reach an alert level, despite serious CO2 levels being reached.

Example of Fatal Levels of CO2 Carbon Dioxide in a Building

Per Levéen has thoughtfully provided the detailed analysis comparing the hazards of elevated carbon dioxide in a building with the accompanying reduction of oxygen (O2 ) in the same space if the percentage of CO2 is increased from a leak from a CO2 gas cylinder. [1]

The data following has been modified by Stephen Fisher, B.Sc, Dip. Ed., Sales Director of K.D.Fisher & Co., Pty. Ltd.[3]

FACT: 100 liters of air contains:

Preliminary Assumptions: If the 100 litres is contained in a balloon like membrane, then 1.4 litres of gas can be added, at the same pressure.

If we add 1.4 litres of CO2 to this mixture, we will get 101.4 litres of air which has an elevated CO2 content, and a reduced oxygen content, see the calculation immediately below:

Carbon Dioxide: (1.4 + 0.04) / 101.4 = 0.014 = 1.42 % CO2 by volume in air

This is is an increase in CO2 percentage of 35.5 times above the “normal level” of 0.04% CO2 by volume in air. 1.42% CO2 can also be expressed as 14,000ppm (parts per million) CO2.

Oxygen: 20.9 / 101.4 = 0.206 = 20.6 % oxygen.

This is a reduction in the oxygen percentage of 0.3% by volume in air, below the “normal” 20.9% Oxygen by volume in air.

This change in the mix of gases in air when the level of CO2 increased results in a decrease with 1.4% in the oxygen level (and not 6.7% as was stated

at EXAMPLE of Reduced Oxygen Level in a Building)

However, KC Baczewski PE writes that the above calculation should be

((1.4/100)*20.9) = 0.29 %. i.e. a reduction in the “normal” oxygen level of 0.29%

You displace O2 and N2 for a final composition of:

Total = 100.00%.

Stephen Fisher agrees with this calculation method, which would involve extracting 1.4 litres of air, prior to the addition of the 1.4 litres of CO2 to the remaining 98.6 litres, which restores the total volume to 100 litres.

This calculation has the advantage of providing a standard 100 litres of “air”, and consequently the number of litres of each component corresponds to the % by volume of each component gas of the mixture.[3]

 

Example of Reduced Oxygen Level in a Building

According to EXAMPLE of FATAL LEVELS of CO2 CARBON DIOXIDE in a BUILDING, the math of the following example is not quite correct.

We have kept Dr. Jensen's comments (below) but they should be read together with the detailed example and calculation provided above by Per Levéen.

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.

Document notes:

Original content, since extensively edited and expanded by several experts, this article began in 1985 with a literature search & search on Compuserve's Safety Forum by Dan Friedman. This is background information, obtained from expert sources. However information presented here may be incomplete.

Special thank-you to Thomas K. Keenan + Puschkinallee 6C + 12435 Berlin + F.R.G., for careful reading and editing assistance 29 November 2020.


...

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Or see CARBON DIOXIDE - CO2 FAQs - questions & answers posted originally at this page.

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Carbon Dioxide Articles

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