Photograph of a Drager hand pump used to measure carbon dioxide levels in the environment. Toxicity of Oxygen Gas Exposure, O2
Poisoning Symptoms, Oxygen Gas Exposure Limits, and Links to Toxic Gas Testing Procedures

  • OXYGEN - O2 HAZARDS - CONTENTS: Recommended limits for oxygen gas exposure or usage. Symptoms & effects of exposure to unusually high levels of oxygen. Recommendations for gas measurement instruments, gas detector tubes, Draeger & Gastec tubes & pumps for detection of gases
  • POST a QUESTION or READ FAQs about Oxygen gas exposure limits and toxicity for humans
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Effects of exposure to abnormal levels of oxygen gas:: This document discusses the toxicity and exposure limits for exposure to oxygen gas O2).

We give references and explanation regarding toxicity of oxygen, based on literature search and obtained from the U.S. government and 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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O2 POISONING SYMPTOMS - Oxygen Gas poisoning symptoms

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

Recommendations for tools and methods for detecting gases in buildings or outdoors

The photo shows a Drager colorimetric gas detection tube (also called a "color detector tube") used to test levels of a very wide range of specific gases in air. In an indoor air test (in our laboratory) this particular detector was not being used to measure oxygen, but rather carbon dioxide.

As the blue-stained portion of the tube shows, we found that the CO2 level was about 600ppm which is typical of indoor air and is an acceptable and safe level.

Colorimetric gas detection tubes such as those sold by Drager (or Draeger), Gastec, (two that we use predominantly) and by Kitagawa, and pumps from Drager, Gastec, Komyo Rikagaku Kitagawa, and RAE all work on a similar principle: a measured volume of gas (or air) is drawn through a tube which contains chemicals which change in color in response to the presence of a specific target gas (or range of gases) present in the sample.

By knowing the volume of gas or air sampled, the amount of color change read on a linear scale on the colorimetric gas detection tube can be translated into a very accurate measurement of level of gas present, described in percentage of the total air or in parts per million (PPM).

Other specialized gas detection methods include use of solid state circuity, CMS chips, and special instruments which may be designed to give a quick alarm or a reading in PPM for specific gases. Other gas and air monitoring equipment use pumps which collect and insert a specific volume of air into a vacuum container for later analysis. We've found that for typical field use, the colorimetric gas detector tube method is extremely convenient and very accurate, and it presents minimal requirements for instrument calibration.

What happens if a human breathes too much oxygen rather than too little?

Since we've discussed displacement of and reduction of the level of oxygen by an increase in CO2 or by dangerous carbon monoxide CO levels indoors in occupied buildings, (see links for these topics at the "More Reading" links at the bottom of this article ) let's take a look at the toxicity of oxygen itself and at what happens if the mix of gases in air changes in the opposite direction, increasing rather than decreasing the level of oxygen above normal amounts. Where does this occur? Two examples of exposure of humans to unusually high levels of oxygen occur in "oxygen bars" and in hyperbaric medicine.

Technical note on oxygen toxicity: What about too much oxygen in air: While high levels, even 100% oxygen are used for medical purposes in some cases (hyperbaric oxygen patients breathe 100% O2 at pressures above 2 to 2.4 ATM for 40-60 minutes),breathing high levels of oxygen can be toxic for humans and other animals. (Toxicity of excessive oxygen will depend on the oxygen level, the duration of exposure (breathing it), and individual characteristics).

But breathing high O2 air too long can produce toxic free radicals, producing effects that can be observed clinically in the human lungs or central nervous system. The current recommended limits of oxygen exposure are up to 24 hours with 100% O2, and up to 48 hours with 60% O2. OSHA does not have a permissible exposure limit (PEL) for oxygen.

What are the symptoms of exposure to elevated levels of oxygen?

The symptoms of excessive oxygen exposure include the following: (some or all of these might occur)

What are the medical effects or symptoms of prolonged exposure to 100% oxygen?

If a person (say a medical patient undergoing hyperbaric treatment at high levels of oxygen and at increased pressure) is breathes 100% oxygen for more than a day (24 hours) s/he may show the symptoms we listed just above, and also the following:

Reader Question: At what level does Oxygen become toxic ?

05/04/2015 Anonymous said:
What is the ppm at which oxygen becomes toxic?


Anon, OSHA has not set a PEL for Oxygen.

Bert originally described that CNS toxicity occured at oxygen pressures of > 3 ATA, it may however, occur at lower pressures if exposure is prolonged. Note that this is at three atmospheres of pressure. Though early manifestations are variable, twitching of perioral and small muscles of the hand is a fairly constant feature. Intense peripheral vasoconstriction due to hyperoxia and diaphragmatic twitching can result in facial pallor and ‘cogwheel’ breathing, respectively4,7. Continuation of exposure can lead to vertigo and nausea followed by altered behaviour, clumsiness, and finally convulsions. The convulsions are usually tonic-clonic, and the patient has no memory of the crisis4,8. A neurogenic pulmonary oedema concomitant with the convulsions has also been reported . The factors aggravating the CNS toxicity are raised pCO2, stress, fatigue, cold, and dietary deficiency of trace elements such as selenium, zinc and magnesium1,4,10. CNS toxicity is mainly due to oxidation and polymerisation of -SH groups of enzymes leading to their inactivation, which in turn results in cellular damage.

... Pulmonary effects of oxygen toxicity can occur after a prolonged exposure to oxygen > 0.5 ATA. Symptoms appear after a latent period whose duration decreases with increase in pO2 . In normal humans, the first signs of toxicity appear after 10 hours of oxygen at 1 ATA. (Chawla (2001) - According to Patel et als (JIACM 2003; 4(3): 234-7)


Continue reading at GAS EXPOSURE LIMITS & STANDARDS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.



Or see CONVERT PPM to % CONCENTRATION To convert between % and ppm

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