Oxygen Depletion

Oxygen (O2) is an essential gas which supports our breathing and our lives. The air is made up of various different gases, including oxygen and carbon dioxide. The normal concentration of oxygen in the ambient air is around 20.9% v/v. When the amount of oxygen in the air falls below 19.5% v/v then it’s considered to be oxygen-deficient.

Oxygen deficiency cannot be detected by human senses, this is why gas detection equipment is absolutely crucial and in some cases breathing protection.

Causes of Oxygen Deficiency

Oxygen deficiency may occur if gases, other than oxygen, are added or mixed with your breathing air. This dilutes the oxygen concentration, therefor causing an oxygen deficiency. If there are inert gases present in the atmosphere, such as nitrogen, argon or helium, then a person’s physical and mental efficiency is affected and fainting may occur without warning. Below 11% concentration means there will be a very high risk of death that will occur through asphyxiation.

The evaporation of liquefied gases, such as liquid nitrogen, can produce enormous volumes of gas. This in turn can lead to oxygen deficiency, especially in an area with inadequate ventilation.

Other causes include gas leaks from things like pipework or in poorly ventilated areas.


Effects of Oxygen Deficiency (not taking into consideration the presence of other gases)

The following effects are based on the oxygen concentration within the air. It does not take in to consideration the inhalation of other gases. If the oxygen concentration inhaled is less than 18 % then this will immediately be hazardous. If there’s no oxygen present then the inhalation of only 1-2 breaths of nitrogen or other inert gas will cause sudden loss of consciousness and can cause death.

A person who encounters an oxygen-deficient atmosphere which is slightly under the normal concentration will start to have impair concentration and decision-making. However, this won’t be as noticeable to the individual at this stage. It’s worth noting that if the atmosphere does fall to this level then it’s still appropriate to carry out a risk assessment to determine the cause and if it’s safe for the person to continue working.

When the oxygen level falls between 11-18% then the person will face a reduction in their physical and intellectual performance, without actually being aware of it.

If the concentration continues to fall, the person will faint within a few minutes, without warning. At worst, the risk of death is increased below 11%. Resuscitation may be possible between 6-8% but only if carried out immediately.

When the oxygen concentration is between 0-6% then fainting will be almost immediate and the person will face being brain damaged, even if they are rescued.

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