IATA Class 4 Division 4.2 Substances Liable to Spontaneous Combustion

Division 4.2 substances include those that are liable to spontaneous heating under normal conditions of transport, or those substances that heat up with contact with air and have a potential to catch on fire. These substances are classified as either pyrophoric substances or self-heating substances.

Pyrophoric substances and mixtures ignite within 5 minutes of coming in contact with air. Even small quantities of these substances are liable to spontaneously combust. Division 4.2 includes pyrophoric solids and liquids, and they are all assigned to Packing Group I.

Self-heating substances undergo a gradual reaction with oxygen that generates heat. If the rate of heat production exceeds the rate of heat loss, then the temperature of the substance will rise, and over time, that can lead to self-ignition and combustion. Self-heating substances do not require any additional energy source. Unlike pyrophoric substances, self-heating substances will ignite only in large quantities and after long periods of time. These substances are assigned to either Packing Group II or III, depending on the test results as described in Subsection 3.4.2.4.2.

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