User Guide to Thresholds and Classification - Environmental ...

72User Guide for Thresholds and Classificationsthe finest particle form in which that substance is reasonably capable of being used or rendered; orwhere it is likely or known that more than 10% of the mass of the substance will crumble into a finerparticle form, then that finer form.6.5.3. Classification criteria for subclass 4.3 substances which in contact with water emitflammable gases (equivalent to UN division 4.3)There are three classification categories to subclass 4.3, substances that in contact with water emitflammable gases. The criteria for inclusion in these categories are as follows.Category A (high hazard) – classification 4.3A (equivalent to UN PG I)Any substance that:a. emits a gas that ignites when a small quantity of the substance is brought into contact with waterwhen tested in accordance with the procedure set out in Test N.5 (para 33.4.1.4, UN Manual ofTests and Criteria); orb. reacts readily with water at ambient temperatures such that the rate of evolution of flammable gas isgreater than or equal to 10 L of gas per kilogram of substance over any one minute, when the rate ofemission of flammable gas is determined in accordance with Test N.5 (para 33.4.1.4, UN Manual ofTests and Criteria).Category B (medium hazard) – classification 4.3B (equivalent to UN PG II)Any substance that reacts readily with water at ambient temperatures such that the maximum rate ofevolution of flammable gas, determined in accordance with the procedures of Test N.5 (para 33.4.1.4,UN Manual of Tests and Criteria), is greater than or equal to 20 L of gas per kilogram of substance perhour, but less than 10 L per kilogram per minute.Category C (low hazard) – classification 4.3C (equivalent to UN PG III)Any substance that reacts slowly with water at ambient temperatures such that the maximum rate ofevolution of flammable gas, determined in accordance with the procedures of Test N.5 (para 33.4.1.4,UN Manual of Tests and Criteria), is equal to or greater than 1 L of gas per kilogram of substance perhour, but less than 20 L per kilogram per hour.6.5.4. DiscussionThe above classification is in accordance with section 2.4.4.3 of the UN Model Regulations for division 4.3,PGs I, II, and III.Screening procedures for substances that in contact with water may react to emit flammable gasesA substance does not need to be evaluated as a substance that may react with water to emit flammablegases if:the chemical structure of the substance does not contain metals or metalloids; orexperience in production or handling shows that the substance does not react with water (for example,the substance is manufactured in water or washed with water); orthe substance is known to be soluble in water to form a stable mixture.January 2012 EPA0109