Class 4, Flammable Solids; Substances Liable to Spontaneous Combustion; Substances That on Contact with Water Emit Flammable Gases
(Water-reactive Substances)

2.21 General

Substances are included in Class 4 if they are flammable solids, substances liable to spontaneous combustion or substances that on contact with water emit flammable gases (water-reactive substances) and meet the criteria for inclusion in one of the divisions and packing groups of Class 4.

2.22 Divisions

Class 4 has three divisions:

(a) Class 4.1, Flammable Solids, which consists of substances that are

(i) readily combustible, as determined in accordance with section 2.4.2.2 of Chapter 2.4 of the UN Recommendations,

(ii) under normal conditions of transport, liable to cause fire through friction,

(iii) explosives desensitized through wetting or dilution so that they are not included in Class 1, Explosives, but are liable to explode if not wetted or diluted sufficiently to suppress their explosive properties,

Substances that have one of the following UN numbers satisfy the criterion in subparagraph (iii): UN1310, UN1320, UN1321, UN1322, UN1336, UN1337, UN1344, UN1347, UN1348, UN1349, UN1354, UN1355, UN1356, UN1357, UN1517, UN1571, UN2555, UN2556, UN2852, UN2907, UN3270, or UN3319.

(iv) self-reactive substances that are liable to undergo a strongly exothermic decomposition even without the participation of oxygen (air), as determined in accordance with section 2.4.2.3 of Chapter 2.4 of the UN Recommendations, but Class 4.1 does not include substances that have

(A) a primary class of Class 1, Explosives, Class 5.1, Oxidizing Substances, or Class 5.2, Organic Peroxides,

(B) a heat of decomposition less than 300 J/g, or

(C) a self-accelerating decomposition temperature (SADT) that is greater than 75°C for a 50 kg means of containment, as determined in accordance with section 2.4.2.3.4 of Chapter 2.4 of the UN Recommendations,

(v) identified by the UN number UN2956, UN3241, UN3242 or UN 3251, or

(vi) listed in Schedule 4;

If the substance to be classified appears as an entry in the first column of Schedule 4, the UN number is the one shown in the last column. That UN number is then used as the entry point into Schedule 2 to identify the remaining classification elements for the substance.

(b) Class 4.2, Substances Liable to Spontaneous Combustion, which consists of

(i) pyrophoric substances that spontaneously ignite within 5 minutes after coming into contact with air, as determined in accordance with section 2.4.3.2 of Chapter 2.4 of the UN Recommendations, or

(ii) self-heating substances that, when in large amounts (kilograms), spontaneously ignite on contact with air after long periods (hours or days), as determined in accordance with section 2.4.3.2 of Chapter 2.4 of the UN Recommendations; and

(c) Class 4.3, Water-reactive Substances, which consists of substances that, in tests performed in accordance with section 2.4.4.2 of Chapter 2.4 of the UN Recommendations, evolve a flammable gas at a rate greater than 1 L/kg of substance per hour or spontaneously ignite at any step in the test procedure.

(1) Solids included in Class 4.1, Flammable Solids, are included in the following packing groups:

(a) Packing Group I, if the substances meet the criteria in subparagraph 2.22(a)(iii), except that substances that have the following UN number are included in Packing Group II: UN2555, UN2556, UN2557, UN 2907, UN3270, UN3319 and UN3344;

(b) Packing Group II, if

(i) the substances meet the criteria for inclusion in Class 4.1 in subparagraph 2.22(a)(iv) or (v), except that substances that have the following UN number are included in Packing Group III: UN2956, UN3241 and UN3251,

(ii) in tests referred to in section 33.2.1 of Part III of the Manual of Tests and Criteria for readily combustible solids, excluding metal powders, the burning time of the substances is less than 45 seconds and the flame passes the wetted zone, or

(iii) in tests referred to in section 33.2.1 of Part III of the Manual of Tests and Criteria, for readily combustible solids that are powders of metals or metal alloys, the zone of reaction of the substances spreads over the whole length of the sample in 5 minutes or less; or

(c) Packing Group III, if

(i) in tests referred to in section 33.2.1 of Part III of the Manual of Tests and Criteria, for readily combustible solids, excluding metal powders, the burning time of the substances is less than 45 seconds and the wetted zone stops the flame propagation for at least 4 minutes,

(ii) in tests referred to in section 33.2.1 of Part III of the Manual of Tests and Criteria, for readily combustible solids that are powders of metals or metal alloys, the zone of reaction of the substances spreads over the whole length of the sample in more than 5 minutes but not more than 10 minutes, or

(iii) the substances are solids that are liable to cause fire through friction.

(2) Substances included is Class 4.2, Substances Liable to Spontaneous Combustion, are included in the following packing groups:

(a) Packing Group I, if the substances are pyrophoric solids or liquids;

(b) Packing Group II, if the substances are self-heating substances that give a positive result, as determined in accordance with section 2.4.3.2 of Chapter 2.4 of the UN Recommendations using a 25 mm sample cube at 140º C; or

(c) Packing Group III for all other substances.

(3) Substances included is Class 4.3, Water-reactive Substances, are included in one of the following packing groups:

(a) Packing Group I, if the substances

(i) react vigorously with water at ambient temperatures and demonstrate a tendency for the gas produced to ignite spontaneously, or

(ii) react readily with water at ambient temperatures so that the rate of evolution of flammable gas is greater than or equal to 10 L/kg of substance over any one minute;

(b) Packing Group II, if

(i) the substances react readily with water at ambient temperatures so that the rate of evolution of flammable gas is greater than or equal to 20 L/kg of substance per hour, and

(ii) the criteria for inclusion in Packing Group I are not met; or

(c) Packing Group III, if

(i) the substances react slowly with water at ambient temperatures so that the rate of evolution of flammable gas is greater than or equal to 1 L/kg of substance per hour, and

(ii) the criteria for inclusion in Packing Group I or II are not met.