Explosion Characteristics of Hydrogen-air and Hydrogen-Oxygen Mixtures at Elevated Pressures

An essential problem for the operation of high pressure water electrolyzers and fuel cells is the permissible contamination of hydrogen and oxygen. This contamination can create malfunction and in the worst case explosions in the apparatus and gas cylinders. In order to avoid dangerous conditions the exact knowledge of the explosion characteristics of hydrogen/air and hydrogen/oxygen mixtures is necessary. The common databases, e.g. the CHEMSAFE® database published by DECHEMA, BAM and PTB, contains even a large number of evaluated safety related properties, among other things explosion limits which however are mainly measured according to standard procedures under atmospheric conditions.
Within the framework of the European research project “SAFEKINEX” and other research projects the explosion limits, explosion pressures and rates of pressure rise (KG values) of H2/air and H2/O2 mixtures were measured at elevated conditions of initial pressures and temperatures by the Federal Institute of Materials Research and Testing (BAM). Empirical equations of the temperature influence could be deduced from the experimental values. An anomaly was found at the pressure influence on the upper explosion limits of H2/O2 and H2/air mixtures in the range of 20 bars. In addition explosion pressures and also rates of pressure rises have been measured for different hydrogen concentrations inside the explosion range. Such data are important for constructive explosion protection measures. Furthermore the mainly used standards for the determination of explosion limits have been compared. Therefore it was interesting to have a look at the systematic differences between the new EN 1839 tube and bomb method, ASTM E 681-01 and German DIN 51649-1.