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The paper provides a summary of safety characteristics of hydrogen and hydrogen fuel gases. The inves-tigations focus on water electrolysis, the feeding of hydrogen into the natural gas grid and the use ofhydrogen for the fermentation process in biogas plants. The safety characteristics of hydrogen such as avery low minimum ignition energy, very large explosion range and high flame velocity with the resultingrapid pressure increase of hydrogen explosions are of particular importance for explosion protection andthey differ strongly from those of natural gas. Explosion ranges of hydrogen-methane-carbon dioxidemixtures have been measured for the use of hydrogen in biomethane production. The paper also showsand discusses explosion ranges of hydrogen and hydrogen-natural gas mixtures. Pressure and tempera-ture dependencies of the explosion limits of mixtures were investigated. Furthermore, pressure rise rates(KGvalues) were measured with regard to constructive explosion protection. The maximum experimen-tal safe gaps were determined for the classification of the mixtures and assignment to explosion groupsaccording to the European ATEX directives. It was found that admixture of 10% hydrogen to natural gashas only a minor influence on the safety characteristics of gas explosions.
Most fluorinated hydrocarbons that shall replace refrigerants with high GWP, like R134a, are flammable. For evaluating inertization measures for explosion protection, flammability of low-GWP refrigerants R1234yf, R32 and R1132a blended with carbon dioxide, nitrogen and argon were studied experimentally in a closed autoclave at atmospheric conditions. Furthermore, a calculation method was adapted to reduce the experimental costs for flammability studies on these gas mixtures. For igniting R1234yf in the closed autoclave a newly developed ignition system was used that allows generating electric arcs with high ignition energy. Gas mixtures containing the mildly flammable R1234yf and R32 could be inerted by adding much less inert gas than mixtures containing R1132a, which is more similar to unfluorinated hydrocarbons regarding the explosion regions. By using the adapted model of constant adiabatic flame temperature profiles estimating the explosion limits of fluorinated hydrocarbons was possible with similar accuracy as for unfluorinated hydrocarbons.
Keywords: Explosion Protection, Inertization, Flammability, HFOs, HFC., R1234yf, R32, R1132a
The safety characteristics of flammable gases and liquids are required when identifying potentially explosive mixtures and taking appropriate actions concerning explosion protection. Examples are given here of the safe handling and evaluation of hazards during the processing, storage, transport, and disposal of flammable liquids and gases. The CHEMSAFE database is presented as a reliable source of safety characteristic data, and its new open-access version is introduced. CHEMSAFE currently contains assessed properties for about 3000 liquids, gases and mixtures. The lack of a broad experimental foundation in the extensive field of non-atmospheric conditions shows the need for further investigation and standardization. This article summarizes experimental evidence and estimation methods for safety characteristic data under non-atmospheric conditions pointing out current limitations. Suggestions for pre-normative research on safety data under non-atmospheric conditions are given.
Explosion and decomposition limits of flammable and chemically unstable gases were determined experimentally in a closed autoclave with an ignition energy higher than the standard 10 J a 20 J. The ignition source was a lightning arc caused by an exploding wire igniter as described in EN 1839 B. With a newly developed ignition system a graded ignition energy between 3 J and 1000 J was generated. Different types of gases were studied with this ignition system: methane as a typical fuel gas and reference gas for some standards for explosion limit determination, the refrigerant R32 (difluoromethane) as a mildly flammable gas with low burning velocity and high minimum ignition energy compared with methane as well as the chemical unstable gases acetylene, nitrous oxide and ethylene oxide, which can decompose explosively in the absence of air or other oxidizers. It was found that the influence of strong ignition sources on explosion and decomposition limits can be very different for different systems. In case of methane only the upper explosion limit was influenced significantly by the ignition energy, whereas the lower explosion limit was constant. In a standard test vessel with an inner volume of 14 dm3 it was difficult to quantify the upper explosion limit of methane exactly with the strong ignition source, because the explosion pressure did not increase abruptly near the explosion limit, but steadily over a large concentration range. Probably a larger explosion vessel is more appropriate in this case. In case of R32 however, it was the lower explosion limit that was influenced significantly by the ignition energy and not the upper explosion limit. A particularly strong dependency from the ignition energy was found for the decomposition limits of the chemically unstable gases in nitrogen. Here special regard is necessary in practical applications, if uncommonly strong ignition sources cannot be excluded.