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.

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Information about Concentrations of Carbon Dioxide - CO2 in Air\

Article Series Contents

Carbon Dioxide Concentrations in Air & The Effects of CO2 at Various Levels

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.
  • 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.

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

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

The photo (left) 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], 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 POISONING SYMPTOMS - 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.

- 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.

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:

  • 20.9 liters of oxygen (20.9%)
  • 0.04 liters of CO2 (0.04%)

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 bolume 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:

  • N2 (Nitrogen) = (79.1/100)*(100-1.4) = 77.99%
  • O2 (Oxygen) = (20.9/100)*(100-1.4) = 20.61%
  • Ar (Argon) = 1%
  • CO2 (Carbon Dioxide) = 1.4%

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]

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 shown below at Example of Reduced Oxygen Level in a Building, 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.

Example of a Carbon Dioxide (CO2) reaching 5% of the 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.

 

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%


A 5% level of CCO2 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 Reduced Oxygen Level in a Building

According to Example of Fatal levels of CO2 Carbon Dioxide in a Building (above), 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, began in 1985 with a literature search & 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 information presented here is not authoritative and may be incomplete.

 

Continue reading at CO2 EXPOSURE LIMITS or select a topic from the More Reading links shown below.

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