What classification is given to spontaneously combustible materials under UN HCS?

Spontaneously combustible materials are classified under Class 4 according to the United Nations Hazard Classification System (UN HCS). This classification encompasses substances that can ignite spontaneously in air at or above ambient temperatures, commonly referred to as "self-heating" materials.

Class 4 is subdivided further into three divisions: Division 4.1 includes flammable solids, Division 4.2 is for materials that can self-heat, and Division 4.3 pertains to materials that emit flammable gas when in contact with water. The categorization of spontaneously combustible materials within Class 4 highlights the need for special handling, storage, and transportation measures to mitigate the risks of fire and explosion associated with these substances.

In contrast, Class 3 covers flammable liquids, Class 5 deals with oxidizing agents and organic peroxides, while Class 6 encompasses toxic and infectious substances. Each of these classes is based on specific characteristics and risks associated with different types of hazardous materials. Understanding these distinctions is essential for ensuring effective safety measures in handling various hazardous materials.