User Guide to Thresholds and Classification - Environmental ...

87User Guide for Thresholds and Classificationsmass of 65% aqueous nitric acid and cellulose, under the same conditions when tested asprescribed for liquids in Test O.2 (para 34.4.2, UN Manual of Tests and Criteria), and the criteria fora classification category A or category B are not met.Classification 5.1.2A (oxidising substances that are gases) (equivalent to UN division 2.2 (in part))A substance is classified as an oxidising gas if:a. the substance is listed in the UN Model Regulations as having a classification of UN division 2.2 anda classification, division, or subsidiary risk of an oxidising substance, division 5.1; orb. the substance is a gas and when tested or evaluated as prescribed in section 5 of ISO 10156:1996for determining the oxidising power of gases and gas mixtures it is found to cause or contribute tocombustion of other material at a faster rate than air does.7.5.3. DiscussionMultiple hazards classificationA substance may have different hazard classifications where this is necessary to indicate different hazardlevels according to:different physical forms of the substance, if it is a solid; anddifferent concentrations of the substance, if it is a mixture.Threshold tests for substances with oxidising propertiesThe approach taken to defining tests and criteria for thresholds for oxidising substances is to specify thespecific testing procedures based on those in the UN Manual of Tests and Criteria, and to provide thatsubstances listed in the UN Model Regulations be included. The latter is to minimise the need for re-testingsubstances already accepted as having an oxidising property. This approach has been taken because thereappears to be no other recognised procedures in common use. Similarly, for gases, the criterion used is asingle test procedure laid out in ISO 10156:1996.Test proceduresThe test methods set out in the UN Manual of Tests and Criteria are designed to observe the effects of thetest substance and cellulose mixture, relative to a mixture made up of a reference substance and cellulose,under set conditions. Consequently, the description of the test refers to the observed effects of thesubstance and cellulose mixture, not the ‗substance‘ itself. For solids, two different mixing ratios of 1:1 and4:1 of substance to cellulose are tested, because a test substance may react differently with each ratio.The description for the assessment of mixtures follows current best practice as described in the UN Manualof Tests and Criteria. Generally, a substance with an oxidising property should be mixed with only‗compatible substances‘, that is, substances that it will not react with to cause a fire or combustion. For amixture, the classification is based on the component substance if only one component has an oxidisingproperty sufficient to meet the test for classification, or the mixture is tested and classified accordingly.SolidsJanuary 2012 EPA0109