User Guide to Thresholds and Classification - Environmental ...

69User Guide for Thresholds and Classificationsa positive result with a 25 mm cube of the substance at 140ºC (the criteria are in paras 33.3.1.6.4.1 and33.3.1.6.4.3).Category C (self-heating substances: low hazard) – classification 4.2C (equivalent to UN PG III)‗Self-heating substances‘, which do not meet the criteria for subclass 4.1.2, that fail to qualify forcategory A or B, but when tested in accordance with Test N.4 (section 33.3.1.6, UN Manual of Tests andCriteria), obtain a positive result in a test using:a. a 100 mm sample cube at 140°C and the substance is in a volume of more than 3 m3; orb. a 100 mm sample cube at 140°C and a positive result is obtained in a test using a 100 mm cube at120°C and the substance is in a volume of more than 450 L; orc. a 100 mm sample cube at 140°C and a positive result is obtained in a test using a 100 mm cube at100°C.6.4.4. DiscussionSubstances giving a positive result with tests for both subclass 4.1.2, self-reactive substances, and subclass4.2, substances liable to spontaneous combustion, should be classified as subclass 4.1.2, self-reactivesubstances.The classification criteria and UN test methods referred to above are as follows.Category A (equivalent to UN PG I)‗Pyrophoric substances‘ are substances that ignite within five minutes on contact with air under thefollowing test conditions.a. For pyrophoric solids, if when 1–2 mL of the powdery substance is poured from a 1 m height onto anon-combustible surface, it ignites during dropping or within five minutes of settling. This procedureshould be performed six times unless a positive result is obtained earlier. If ignition occurs in one ofthe tests, the substance is in category A. The procedure set out in section 33.3.1.4, p 328, of the UNManual of Tests and Criteria, should be followed in determining this result.b. For pyrophoric liquids:i. If, when 5 mL of the liquid is poured into a porcelain cup of about 100 mm diameter (filled withdiatomaceous earth or silica gel at room temperature to a height of about 5 mm), the liquidignites when exposed to air for five minutes. This procedure should be performed six timesunless a positive result is obtained earlier. If no ignition occurs then the second part of the testbelow is performed to determine if it chars or ignites a filter paper.ii. A 0.5 mL test sample should be delivered from a syringe to an indented dry filter paper. The testshould be conducted at 2 Observations are made tosee if ignition or charring occurs on the filter paper within five minutes of addition of the liquid.This procedure should be performed three times using fresh filter paper each time unless apositive result is obtained earlier.iii. If the liquid ignites in the first part of the test, or it ignites or chars the filter paper, it is above thecriteria for category A.January 2012 EPA0109