Explosion class 8 is not a commonly used term. However, based on the search results, it seems that "explosion" refers to a sudden and violent release of energy, resulting in the rapid expansion of gases, intense heat, and the generation of a shockwave. It is a type of combustion during which a huge amount of heat and light is evolved with a boom, along with the production of gas. An explosion occurs when a sudden reaction takes place with the release of heat and light and evolution of a large amount of gas takes place. Examples of explosions include firecrackers.