CLASS 4 - FLAMMABLE SOLIDS
SUBSTANCES LIABLE TO SPONTANEOUS COMBUSTION;
SUBSTANCES WHICH, IN CONTACT WITH WATER, EMIT FLAMMABLE GASES

4.1 In this Code, class 4 deals with substances, other than those classified as explosives, which, under conditions of transport, are readily combustible or may cause or contribute to a fire. Class 4 is subdivided as follows:

Class 4.1 Flammable solids
This Class 4.1 includes the following types of substances:
(1)Flammable solid
Readily combustible solids and solids which may cause fire through friction;
(2)Self-reactive substances
Thermally unstable substances liable to undergo a strongly exothermic decomposition even without participation of oxygen;
(3)Solid desensitized explosives
Explosive substances which are wetted with water or alcohol or are diluted with other substances to form a homogeneous solid mixture to
suppress their explosive properties; and
(4)Polymerizing substances and mixtures (stabilized)
Substances which, without stabilization, are liable to undergo a strongly exothermic reaction resulting in the formation of larger molecules or
resulting in the formation of polymers under conditions normally.

Class 4.2 Substances liable to spontaneous combustion
Substances (solids and liquids) which are liable to spontaneous heating under normal conditions encountered in transport, or to heating up in contact with air, and being then liable to catch fire;

Class 4.3 Substances which, in contact with water, emit flammable gases
Substances (solids and liquids) which, by interaction with water, are liable to become spontaneously flammable or to give off flammable gases in dangerous quantities.

4.2 As referenced in this chapter, test methods and criteria, with advice on application of the tests, are given in the United Nations Manual of Tests and Criteria, for the classification of following types of substances of class 4:

.1 Flammable solids (class 4.1);

.2 Self-reactive substances (class 4.1);

.3 Pyrophoric solids (class 4.2);

.4 Pyrophoric liquids (class 4.2);

.5 Self-heating substances (class 4.2); and

.6 Substances which, in contact with water, emit flammable gases (class 4.3).

Test methods and criteria for self-reactive substances are given in Part II of the United Nations Manual of Tests and Criteria, and test methods and criteria for the other types of substances of class 4 are given in the United Nations Manual of Tests and Criteria, Part III, chapter 33.