BRHS /
Asphyxiation by HydrogenHydrogen 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).
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