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Oxygen (O2): Gas Hazards & Occupational Health

Gas Chemical Details

Oxygen, the most abundant element in the earth’s crust is of great interest due to the fact that it’s essential in the respiratory processes of most living cells. It is found in both the air we breathe and the water we drink. In normal conditions oxygen is a colourless and odourless.

Occupational Health exposure standards

When detecting Oxygen, gas detectors are used for measuring both the depletion and enrichment of Oxygen. The thresholds for these alarm points tend to be 23.5% (enrichment) and 19.5% (depletion).

Effect on humans of gas hazard

We all need to breathe the air to live; air is made up of several different gases including Oxygen. Normal ambient air contains an Oxygen concentration of 20.9% v/v. When the Oxygen level dips below 19.5%, the air is considered Oxygen-deficient.

The following table demonstrates the effects of oxygen depletion on humans.

Concentration of Oxygen (v/v)Effects                                                                                      
20.9%Oxygen concentration of Air
19.5%Minimum “Safe Level”
17.0%Impairment of judgement starts to be detected
16.0%First signs of anoxia (dizziness, light-headedness)
16%-12%Breathing and pulse rate increases, muscular co-ordination starts to beome impaired
14%-10%Consciousness continuous, abormal fatigue and distrubed respiration
10%-6%Nausea, vomiting, inability to move freely and loss of consciousness may occur
<6%Convulsive movements and gasping respiration occurs, respiration stops and a few minutes later heart action ceases.


It is often forgotten that Oxygen enrichment can also cause a risk. While there are no adverse health effects from oxygen levels greater than the normal background levels of 20.9%, oxygen levels that exceed 23.5% present a serious fire danger.  At levels of 25%+ items such as clothing can spontaneously combust.

Causes or source of the gas hazard:

Oxygen-deficient atmospheres may be created by a number of different situations, most commonly these include:


  • Oxygen is used up during the combustion process – for example, during cutting or welding and the running of internal combustion engines.

Gaseous Displacement

  • Oxygen can be replaced by other gases used in industrial processes – for example, welding gases
  • Inerting of tanks with CO2 or Argon will deplete the oxygen level
  • Oxygen can also be replaced by gases leaking into an enclosed space through drains or other openings


  • Rusting metals or oxidation reduces oxygen
  • Decomposition of organic materials
  • Ripening of fruits

Humidity and Temperature

  • Increase of temperature and humidity will reduce the oxygen concentration
Humidity Effect in Air



Applications where oxygen deficiency occurs:

Oxygen deficient atmospheres can be a danger across many applications and industries.  Some examples are holds on barges, sewer systems, wells, grain silos, and process vessels. Lack of oxygen is a leading cause of confined space entry deaths among workers and among those attempting to rescue workers in confined spaces.

Some toxic gases irritate your lungs or have a taste or smell to warn you that they are present, but air that is low in oxygen has no warning properties: you can’t smell, taste, or see any difference when air is low in oxygen. By the time you feel faint or dizzy, you may not have enough energy or alertness to escape.



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