Posted By Martin Thorpe I am seeking what would be an equivalent of an occupational exposure limit (OEL) for oxygen. I understand that oxygen depletion is often encountered when other substances that have OELs displace oxygen, but this is not relevant for my particular query. I am also aware that any deviation from the normal concentration of oxygen in air of 20.8% is not desirable. However, I am seeking written guidance on the level at which property should be evacuated. My recollection is that this level should be set at 18% v/v. I have found no statutory guidance that proposes concentrations at which action should be taken. Are you aware of any statutory or other health and safety guidance that might provide quoted concentrations?

Posted By Malcolm Shepperson Hi Martin This is a outline of effects of oxygen depletion that I took from the Oxford University Liquid Nitrogen policy that is available on the Web O2 (vol. %) Effects and symptoms 18-21 No discernable symptoms can be detected by the individual 11-18 Reduction of physical and intellectual performance 8-11 Possibility of fainting within a few minutes without prior warning. Risk of death below 11 vol.% 6-8 Fainting occurs after a short time. Resuscitation possible if carried out immediately 0-6 Fainting almost immediate. Brain damage may occur, even if rescued.

Posted By Mike Palfrey Hi Martin, At my company we use 19.5 % as a minimum before we need to take oxygen depletion measures and 23% before we consider oxygen enrichment as a hazard. I strongly recommend the use of an Oxygen meter in any atmosphere that is likely to contain oxygen at any concentration other than 21% Hope this helps Mike

Posted By Dean Cross Hi Martin In areas where the oxygen concentration could deviate from 21%, such as cryogenic stores, we recommend oxygen monitors and alarms set at 2 levels. upper level should be set at 19.5 vol % O2 (if this alarm is triggered, then there should be urgent investigation and corrective action) lower level should be set at 18 vol % O2 (if this alarm is triggered, then the area should be evacuated immediately). Dean