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ISO 10156:2010 contains a test method and a calculation method for flammability of gases and gas mixtures for the selection of cylinder valve outlets. The calculation method is used also to classify gas mixtures according to the national and international dangerous goods and dangerous substances regulations, e.g. according to the UN Recommendations on the Transport of Dangerous Goods (UN TDG) and the Globally Harmonized System of Classification and Labelling of Chemicals (UN GHS). The calculation method for gas mixtures requires substance parameters of the single components. These are the coefficients for the fire potential (Tci) and for inerting ability, the so-called nitrogen equivalence (Kk), which have been estimated conservatively by means of flammability data.
BAM checked Tci and Kk values of ISO 10156:1996 using three-component diagrams (Flammable gas-Inert-Air) of the CHEMSAFE® database. The experimental fundamentals and the principles of the calculation method are summarized in this paper. The revised data for Tci and Kk values were adopted in the tables of ISO 10156:2010.
Furthermore, subcategorization of flammable gases has been proposed by a UN working group and shall be implemented in the GHS in the meantime. The subcategorization requires the lower flammability limit (LFL) as an additional indicator. Therefore, a test method and a calculation method for LFL were proposed by BAM and have been implemented in the new draft of ISO/CD 10156:2016.
The calculation method for gas mixtures is based on Le Chatelier’s rule and was extended by using the Kk values for inert components in the mixture. The calculated LFLs of methane-inert gas mixtures were compared with experimental values for different types of inert gases. It could be shown that calculated LFLs are in good agreement with experimental values if the Kk values derived from three-component flammability diagrams are used. Although using the Kk values of ISO 10156:2010 leads to higher deviations, the results are still on the safe side.
The classification of flammable gas mixtures is based on either testing or calculation methods proposed by the revised international standard ISO 10156. This standard is used for classification of physical hazards in Chapters 2.2 and 2.4 of the UN Globally Harmonized System of Classification and Labelling of Chemicals (GHS) and in the UN Recommendations on Transport of Dangerous Goods (TDG). The test methods of flammability and oxidizing potential in this standard were developed by BAM. Earlier versions of this standard are not based on triangular diagrams and on the reference combustible substance 'ethane'. The old material characteristics, especially in case of oxidizing potential, are based mostly on practical experience without any quantifiable test results. First time it is possible to compare experimental results from the CHEMSAFE database with the newly developed calculation method. In this paper the basic principles of the calculation methods are presented and the methods are validated by examples. A comparison of experimental flammability data with classification results gained by the calculation methods of ISO 10156 is demonstrated.
Ternary systems, which contain flammable gas, inert gas and air, were studied in order to give the user an evaluation of the ISO 10156 calculation method for the flammability of gas mixtures. While in Part 1 of this article the fire potential of flammable gases was the focal point, the influence of inert gases on the flammability of gas mixtures was studied in Part 2. The inerting capacity of an inert gas is expressed by the dimensionless K value, the so-called coefficient of nitrogen equivalency. The experimental determination of K values is demonstrated by using explosion diagrams. The objective of this study was to compare the estimated results, given by ISO 10156, with measurements of explosion ranges based on the German standard DIN 51649-1, given by CERN and CHEMSAFE. The comparison shows that ISO 10156, Table 1, supplies conservative K values, which can be regarded as safe in all cases. Nevertheless, in a number of cases ISO underestimates the inerting capacity, so that non-flammable gas mixtures are considered flammable.
International and European dangerous substances and dangerous goods regulations refer to the standard ISO 10156 (1996). This standard includes a test method and a calculation procedure for the determination of the flammability of gases and gas mixtures in air. The substance indices for the calculation, the so called Tci values, which characterise the fire potential, are provided as well. These ISO Tci values are derived from explosion diagrams of older literature sources which do not take into account the test method and the test apparatus. However, since the explosion limits are influenced by apparatus parameters, the Tci values and lower explosion limits, given by the ISO tables, are inconsistent with those measured according to the test method of the same standard. In consequence, applying the ISO Tci values can result in wrong classifications. In this paper internationally accepted explosion limit test methods were evaluated and Tci values were derived from explosion diagrams. Therefore, an open vessel method with flame propagation criterion was favoured. These values were compared with the Tci values listed in ISO 10156. In most cases, significant deviations were found. A detailed study about the influence of inert gases on flammability is the objective of Part 2.