User Guide to Thresholds and Classification - Environmental ...

41User Guide for Thresholds and ClassificationsCategory A (high hazard): criterion(b)Category B (medium hazard)Gases that have a flammablerange with air of at least 12%regardless of the lower flammablelimitGases or gas mixtures, other thanthose of high hazard, that at 20°Cand a pressure of 101.3 kPaabsolute have a flammable rangein mixture in airhydrogen, acetyleneChlorotrifluoroethyleneMethyl bromide, ammonia4.1.3. DiscussionClassification criteriaFlammable gas classification 2.1.1A is consistent with division 2.1 of the UN Model Regulations.Flammable gas classification 2.1.1B originates from a December 1996 recommendation of the UnitedNations Committee of Experts on the Transport of Dangerous Goods subcommittee, advising the Inter-Organisation Programme on the Sound Management of Chemicals on flammability.The criterion for category B extends the threshold of gases that are considered flammable gases to suchsubstances as methyl bromide and ammonia. However, these substances are already subject to NewZealand controls under the Dangerous Goods Act 1974.Gas mixturesIf a substance is a gas mixture made up of one or more chemical elements or compounds, and any one ofthose elements or compounds meets one or more of the classification criteria specified above for flammablegases, then the mixture may be assumed to have the same classification as its flammable components,unless it can be shown that the mixture has a different classification according to the above criteria.The means of determining the flammability of gas mixtures (including vapours of substances from othersubclasses), and therefore their classification, is by applying the tests or calculation in accordance withmethods adopted by the International Organization for Standardization (see ISO 10156:1996 (ISO, 1996)).Where insufficient data are available to use these methods, then tests by a comparable method recognisedby the EPA may be used.Further details of test methods are given below.January 2012 EPA0109