User Guide to Thresholds and Classification - Environmental ...

88User Guide for Thresholds and ClassificationsThe particle form of solids is referred to in the definition of the test for solid substances. This recognises thatduring a substance‘s lifecycle, some substances occur in a finer particle form than as originally presented fortesting. However, such an occurrence is of interest only if it will affect the overall hazard classification and isknown to be likely to occur. This avoids unnecessary extra testing.LiquidsThe risk of liquids that are themselves not oxidising but contain anhydrous combustible salts, leading tocombustible residues on exposure to air through evaporation, is a matter for the EPA to consider when itassesses the hazardous properties of the mixture. There is no special classification category to deal withthese liquids.GasesISO 10156:1996 has been adopted as the test method for determining the oxidising potential of a gas.The test details are described in ISO 10156:1996. Substances in gas form that contribute to combustion at agreater rate than does air are considered as having oxidising properties above the threshold. This means thegas in question is more oxidising than air.It should be noted that while the UNCETDG has not settled on a specific test, it has agreed to the definitionof an oxidising gas. The UN Model Regulations suggest using the test method set out in ISO 10156:1996 oran equivalent approved by a competent authority.ISO 10156:1996 also provides calculation methods for determining the flammability of gases.If the oxidising properties of a gas mixture have not been determined by test, then they may be estimated bythe following method.The principle of the method is to compare the oxidising potential of gases in a mixture with the oxidisingpotential of oxygen in air. The concentration of gases in the mixture is expressed as ‗% volume‘.The gas mixture is as oxidising as, or more oxidising than, air, if the following condition is verified:∑ x i c i ≥ 21Where:x i is the concentration of gas i in % volumec i is the coefficient of oxygen equivalency for gas i (specific to each gas)The coefficients used in the above calculation to determine the oxidising capacity of certain gases in amixture with respect to the oxidising capacity of oxygen in air are listed in section 5.2 of ISO 10156:1996.This gives, for example, for oxygen c = 1, and for nitrous oxide, c = 0.6. When no value for c is given for agas in this standard, a value of 40 is attributed to this coefficient.Mixture rulesWhere the substance is a mixture of one or more chemical elements or compounds, any one of which meetsany of the threshold criteria for an oxidising solid or a liquid, then the mixture (that is, as it is imported orJanuary 2012 EPA0109