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

Carbon Dioxide Exposure:

This document discusses the exposure limits for 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.

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

What are the Allowable Limits of CO2 Exposure - Carbon dioxide PEL & TLV by ACGIH, OSHA & NIOSH

Table B-11 & B-21 Acute & Other Health Effects of High Concentrations of Carbon Dioxide

CO2
Concentration
Percent

CO2 ppm

Exposure
Time

Effects
17 - 30 % 170,000 - 300,000 ppm Within 1 minute Loss of controlled and purposeful activity,
unconsciousness, convulsions, coma, death
>10 – 15 % 100,000 - 150,000 ppm 1 - several minutes Dizziness, drowsiness, severe muscle twitching,
unconsciousness
7 – 10 % 70,000 - 100,000 ppm

< 3 minutes 1

1.5 minutes to 1 hour

Unconsciousness, near unconsciousness

Headache, increased heart rate, shortness of breath,
dizziness, sweating, rapid breathing

6 % 60,000 ppm

1 – 2 minutes

#16 minutes

Several hours

Hearing and visual disturbances

Headache, dyspnea

Tremors

4 – 5 % 40,000 - 50,000 ppm Within a few minutes

Headache, dizziness, increased blood pressure,

uncomfortable dyspnea

3 % 30,000 ppm 1 hour Mild headache, sweating, and dyspnea at rest
2 % 20,000 ppm Several hours Headache, dyspnea upon mild exertion
1.5% 15,000 ppm 480 minutes 1  
1 % 10,000 ppm Indefinite 1 Decreased mental performance, Sick Building Syndrome Complaints 2
0.7% 7,000 Weeks Acidosis 3
0.1% 1,000 ppm Indefinite 2 Decreased mental performance, Sick Building Syndrome Complaints 2
0.05% 500 ppm Indefinite 1 Indefinite tolerance

Notes to the table above:

1 Adapted & expanded (to add ppm) from EPA, APPENDIX B-I ACUTE HEALTH EFFECTS of CARBON DIOXIDE [PDF] cited below. Some of this data from table B1 cited in the EPA table in turn cites Compessed Gas Association 1990.

2. ( Erdmann 2002) cited below

3. NCCEH cited below citing in turn (Health Canada 1987)

Carbon dioxide is regulated for diverse purposes but not as a toxic substance. Nevertheless extensive research has documented health and performance impacts of exposure to carbon dioxide at various levels.

In summary, OSHA, NIOSH, and ACGIH occupational exposure standards are 0.5% CO2 (5,000 ppm) averaged over a 40 hour week, 0.3% (30,000 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.

History of Threshold Limit Values TLVs for Carbon Dioxide Exposure Limits [1]

Historical TLVs for CO2 [In the U.S.]

Year Measure Limit [ACGIH]
1946-1947 MAC-TWA 5000 ppm
1948-present TLV-TWA 5000 ppm
1976-1985 TLV-STEL 15,000 ppm
1984 proposed TLV-STEL 30,000 ppm
1985-present TLV-STEL

30,000 ppm - i.e. 3.0% concentration of CO2

 

Notes to the Table Above

Source: ACGIH recommendations for CO2

Carbon Dioxide CO2 Exposure Limit Sources & Research

 




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Reader Comments, Questions & Answers About The Article Above

Below you will find questions and answers previously posted on this page at its page bottom reader comment box.

Reader Q&A - also see RECOMMENDED ARTICLES & FAQs

On 2021-02-25 - by (mod) -

@Tech, Thank you very much for taking time to write about the decimal place error in the chart above. I appreciate all the editing help we can get.

I have edited and so corrected the error; you may need to clear your browser cache to see the updated page.

On 2021-02-25 by Tech

The first chart on this page [https://inspectapedia.com/hazmat/Carbon%20_Dioxide_Exposure_Limits.php#QA] has an error in the table. [Table B-11 & B-21 Acute & Other Health Effects of High Concentrations of Carbon Dioxide]
The bottom left box of the matrix has an incorrect value.
It has: 0.5 ppm
It should be: 0.05 ppm
Compare to values above and the error becomes apparent.

On 2019-11-02 by (mod) - What is the reference for the EPA limit (recommendation) of 1000 ppm?

Matthew:

You are right that the U.S. EPA has not set an explicit exposure limit for carbon dioxide but the agency does cite research and also cites other CO2 exposure standards and limits. I've updated and clarified that point in the article above. Thank you for the helpful query.

The U.S. EPA document discussing sick building syndrome or SBS as I'll cite below gives us:

On 2019-10-29 by Matthew

What is the reference for the EPA limit (recommendation) of 1000 ppm?

On 2018-09-20 by (mod) - 300 - 500 ppm CO2 in outdoor air

Thank you for the comment, Ed.

Normally in outdoor air the CO2 level ranges between 300 or 0.03% concentration to 500 ppm or 0.05% concentration. I have on occasion measured higher concentrations of carbon dioxide in outdoor air, for example near a busy roadway.

Your citation of the amount of H2O or water in air is a different measure entirely

On 2018-09-19 by Ed Golla 1 to 2% H2O in ambient air ?

Don't forget to include the 1 to 2% H2O that is normally present in ambient air.

On 2017-10-06 by Wm.

Wood pellet storage. Our monitors are set to go off at 35ppm. We are told osha standard is 50ppm. If monitor reads 64ppm is it safe to work in?

On 2016-01-18 1 by Anonymous - easier way to come up with the amount of CO using electrochemical sensors

An easier way to come up with the amount of CO for this problem is as follows.
The easiest way that most of us will measure O2 is with an electrochemical sensor. So lets do some math.

An electrochemical sensor is reading O2. O2 is around 20% of fresh air. So the sensor is reading around 1/5 of the atmosphere.

When CO2 is introduced it is not just displacing O2, it is displacing the atmosphere.

We are reading CO2 in ppm. So, 1 million ppm = 100%, 500,000 = 50%, 100,000 = 10%, 10,000 = 1%.

If your O2 sensor goes from 20.9 to 19.5 you would assume that 14,000 ppm of CO2 was there by the sentence above.

BUT, remember the O2 sensor is reading something that is only around 1/5 of the atmosphere. It is not an atmosphere sensor but an O2 sensor. 1/5 has been entered in the formula by this and must be factored in.

Take your 14,000ppm and times it by 5. You now have 70,000ppm

At work I just do it like this.

Every 1/10 that the O2 sensor drops, is equal to 5000ppm.

Example - O2 sensor reading of 20.9 goes down to 20.5. A difference of .4. Take the 4 X 5000 = 20,000ppm of CO2 is there.

On 2015-10-22 by Henry Baxter - calculation of CO2 increase to create an O2 deficiency is incorrect.

Your calculation of CO2 increase to create an O2 deficiency is incorrect.

To reduce your O2 from 20.9% to 19.5% (by 1.4%) you have to account for the dilution of N2 in air as well as O2

A typical N2/O2 ratio of fresh air is 3.77:1, i.e. n2 is 3.77 times more abundant than O2 in air.

Assuming there is dilution only (i.e. no consumption of O2 or other gasses) For a given O2 % you can work out the N2% by multiplying O2%x3.77

e.g. 19.5% O2 would have 3.77 x 19.5 = 73.5% N2 associated with it.

19.5 + 73.5 = 93% i.e. the air fraction makes up 93% of the total.

If the sole diluting agent is CO2 then the balance (7%) is the concentration of CO2 required to get less than 19.5% O2.

Dangerous Levels of CO2 Encountered Outdoors?

Reader Question: 11/25/2014 Rox said:

What is a dangerous level of CO2 outdoors ? I know that we are at about 300-400ppm, at what point it is too dangerous to go outside because of the level on CO2 ?

Reply:

Rox

At our home page for Carbon Dioxide information (CO2 ) you'll find text on the toxicity of this gas.

See CARBON DIOXIDE - CO2

including comparing indoor with outdoor carbon dioxide levels. It would be unlikely for you to encounter toxic levels of CO2 outdoors unless the outdoor area were somehow enclosed on all sides, in still air and was receiving a source of high-concentration of carbon dioxide gas or unless the area is one exposed to high levels of combustion such as Naeher (2000).

In Naeher's research CO2 served principally as an easy-to-measure indicator of other more problematic air quality problems such as high levels of particulates associated with open fires, wood burning stoves, and in some cases gas stoves. In other words, you'd be standing in a smoky area.

The outdoor level of carbon dioxide is relatively constant with occasional peaks

You will find that most research on hazards of gases in outdoor air address carbon monoxide (CO) not carbon dioxide (CO2) - see Curtis (2006) or Thompson (1973).

Outdoor Air Quality and Carbon Dioxide CO2 Levels

Some interesting research that addresses you outdoor air quality question includes the following authors who discuss indoor and outdoor CO2 levels.

Question: OSHA CO2 exposure limits

I believe that you have interchanged 1.4% and 6% under OSHA above. This is very important as it means that an oxygen analyser will not alarm a dangerous concentration of CO2 . - Mark Crittendon 7/20/2012

Reply:

Thanks for looking closely at our CO2 exposure limit data, Mark.
Referring to the OSHA CO2 exposure limits, I have edited our text above to make the calculation of percentage points more clear: (1.4 absolute percentage points divided by 20.9% starting point = 0.06 - or 6% reduction in the CO2 level)

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% (1.4 absolute percentage points divided by 20.9% starting point = 0.06), the CO2 or carbon dioxide level would have to increase to about 1.4% 14,000 ppm.

Thank you for the careful read and the question. We are dedicated to making our information as accurate, complete, useful, and unbiased as possible: we very much welcome critique, questions, or content suggestions for our web articles

 

Question:

"In summary, OSHA, NIOSH, and ACGIH occupational exposure standards are 0.5% CO2 (5,000 ppm) averaged over a 40 hour week, 0.3% (30,000 ppm) average for a short-term (15 minute) exposure"

Sorry is this a mistake, or is there something obvious I am missing?

The TWA or TLV is 0.5%,

but the STEL is 0.3%;

the STEL would be a higher level than the TWA or TLV.

Is the upper limit for continuous 24 hour exposure now 0.1%?

Thank you,

John Brechin 11/13/2012

Reply:

John, in a typo there was a 3,000 that should have been 30,000. The ACGIH and other sources' recommended CO2 TLV-STEL is 30,000 ppm (54,000 mg/m3)

Question: is a level of CO2 at 50 dangerous?

(Mar 15, 2013) France's said:

My brother has co2 level at 50, is this dangerous?

Reply:

France's, I'm sorry but I cannot form an confident opinion from your question as I have no idea what measurement was made, where, nor if we're talking about carbon dioxide level in air, in the bloodstream, or elsewhere

According to Medline, "In the body, most of the CO2 is in the form of a substance called bicarbonate (HCO3,). Therefore, the CO2 blood test is really a measure of your blood bicarbonate level."

If that is the measurement you mean, Medline explains that

"The normal range is 23-29 mEq/L (milliequivalent per liter)."

Your brother should ask his doctor for her opinion about the meaning of his tests.

Question: what kind of test is done for septic odors?

(Dec 19, 2012) test said:

What type of text might you recommend to be done in a place that often has septic odors? I fear that even when the odor is not there that the contaminants are left behind.

Reply:

Test,

While sewer gases or septic system odors contain a complex of gases typically people test for methane in air, and where there has been a sewage spill, a test of surfaces is performed for bacteria such as eColi associated with sewage.

Sewer gas is not itself a Carbon dioxide issue (the subject of this article where you posted the question) and is discussed separately at a couple of articles you'll want to see:

TEST FOR INDOOR SEWER GAS

SEWAGE CONTAMINATION in BUILDINGS

SEWER GAS ODORS - home


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