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Asphyxiation by Hydrogen

Hydrogen is not poisonous, but as with any gas (except oxygen) a risk of asphyxiation exists mainly in confined areas as a result of oxygen depletion. Normal air contains around 20.8 % of oxygen, by volume. Besides the dilution by mixing with other gases, oxygen may be consumed in combustion of hydrogen or other burning gases and may be depleted via condensation on very cold surfaces like liquid hydrogen pools. Thus diluting the oxygen volumetric content below 19.5 % will cause effects on human beings. Alarm levels are generally set at 19 % oxygen. This is less than 2 % below normal levels, so it is important that sensors are stable in order to avoid false alarms. The different stages of asphyxiation at ground level are related to the remaining oxygen concentration as shown in the following table.

Table: Asphyxia – Effect of O2 Concentration from NASA (NASA:NSS:1740:16:1997), partially accomplished and synchronized with DNV data (DNV:2001).

O2 (vol%)Effects and Symptoms
19-21No discernible symptoms can be detected by the individual
15-19Reduction of physical and intellectual performance without the sufferer being aware. Early symptoms in persons with heart, lung, or circulatory problems may be induced
12-15Deeper respiration, faster pulse, poor coordination
10-12Headaches, giddiness, poor judgement, slightly blue lips. Risk of death below 11 vol%, tolerance time 30 min
8-10Nausea, vomiting, unconsciousness, ashenface, fainting within a few minutes without prior warning, mental failure, tolerance time 5 min
6-8Fainting occurs after approximately 3 min. Death in 8 min; 50 % death and 50 % recovery with treatment in 6 min, 100 % recovery with treatment in 4 to 5 min
3-6Coma in 40 s, respiration ceases, death or permanent brain damage, even if rescued
0-3Death within 45 seconds

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Page last modified on February 18, 2009, at 02:29 PM