User Guide to Thresholds and Classification - Environmental ...

71User Guide for Thresholds and ClassificationsPrevious New Zealand criteriaThe Dangerous Goods Act 1974 listed division 4.2, substances liable to spontaneous combustion, beingsolids or liquids possessing the common property of being liable spontaneously to heat and to ignite, ingroups A and B. There is no clear correlation between the HSNO Act categories (UN PGs) and theDangerous Goods Act groups A and B. These Dangerous Goods Act groups are no longer applicable.Example substancesCategory A (equivalent to UN PG I) substances include UN 1366: diethylzinc.Category B (equivalent to UN PG II) substances include UN 1369: p-nitrosodimethylaniline.Category C (equivalent to UN PG III) substances include:UN 1376: iron oxide spent; andUN 2002: celluloid scrap.6.5. Substances dangerous when wet – subclass 4.36.5.1. Threshold criteria for subclass 4.3 substances that in contact with water emitflammable gases (equivalent to UN division 4.3)Certain substances in contact with water may emit flammable gases that can form explosive mixtures withair. This subclass classifies substances where the reaction with water may lead to the development ofdangerous amounts of gases that may be flammable.A substance is considered a subclass 4.3 substance, substances that in contact with water emit flammablegases, within the meaning of the HSNO Act, if it meets one or both of the following criteria.a. Any substance that, when in contact with water, may emit a flammable gas, and when tested inaccordance with Test N.5 (section 33.4.1.4, UN Manual of Tests and Criteria), reacts with water atambient temperatures to produce a gas which ignites spontaneously.b. Any substance that, when in contact with water, may emit a flammable gas, and when tested inaccordance with Test N.5 (section 33.4.1.4, UN Manual of Tests and Criteria), reacts with water toproduce a flammable gas at a rate of 1 L or greater per kilogram of substance per hour.6.5.2. Notes to threshold criteriaThe HSNO Act threshold criteria for subclass 4.3 are equivalent to those for UN division 4.3 as set out inpara 33.4.1.4.4 of the UN Manual of Tests and Criteria.Details of the test method for substances that in contact with water emit flammable gases, are in section33.4.1.4 (Test N.5, UN Manual of Tests and Criteria). No alternative comparable methods have beenrecognised by any overseas national competent authority, so the UN tests have been used to define theHSNO Act threshold.For any substance subjected to the above threshold test method, the result must be determined using either:January 2012 EPA0109