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Lack of oxygen in confined spaces

Lack of breathable air in confined spaces is one of the commonest reasons for accidents where there are multiple deaths among welders and other maintenance workers. HSE investigations usually show that one person collapses, their workmates attempt a rescue and then they collapse too.

Key points

Use of inert gases and some common chemical reactions (eg rusting) can reduce the amount of oxygen inside enclosed spaces such as tanks, pipes and pits.
Working in these locations is dangerous. Before you enter a confined space you need to:

Welding gases such as argon, CO2, nitrogen and helium can displace the air inside enclosed spaces.  Argon and CO2 are relatively ‘heavy’ gases. They can pool in places where you not normally expect to have a problem eg vehicle inspection pits. Sometimes inert gases are used to deliberately replace the air to prevent weld oxidation or reduce the risk of fires. Gases may also build up as they are used during the welding process. If you don’t follow the safe system of work and enter an area where there is a large amount of inert gas, the chances are it’ll be the last thing you do.

If the amount of inert gas is high enough, you won’t cough, splutter, pant or feel breathless. You will simply pass out. It happens so fast you will not be able to rescue yourself. EIS45 Asphyxiation hazards in welding and allied processes provides further information.

If the inert gas has only partially replaced the air, you may feel very weak, tired and confused. You are likely to find you cannot complete simple tasks, including finding the way out. If you aren’t rescued and breathing normal air within a few minutes, you are likely to pass out and eventually die.

Most welding gases, including all the inert gases, have no smell.

There are specific methods for confined space working the free HSE guidance leaflet, Safe Work in Confined spaces , has a useful list of points to consider. HSE publication Safe maintenance, repair and cleaning procedures - L137 has further information on Permit to work systems.

Updated 2014-05-13