It must be chemically unstable. Any initiation must produce an explosion accompanied by large changes in pressure. The material must contain enough oxidizer to maintain the extremely rapid combustion. So in order to be classified as an explosive material the product must meet the criteria by containing fuel and oxidizer (in the proper balance)
Classification of Explosive Materials
Another characteristic of explosive is sensitivity - The amount of external force to initiate the reaction. The force can be anything from shock, impact, friction, electrical discharge, or any other source. Primary Explosives require a small quantity of energy to be initiated and are extremely sensitive but have less power than secondary explosives, they are in detonators and initiation systems (Examples: [Lead azide]?, [Mercury fulminate]?). Secondary Explosives are relatively insensitive but are powerful (Examples: Dynamite, RDX, PETN?)
Detonation (Initiation Sequence)
Also called a firing train, this is the sequence of events which cascade from relatively low levels of energy to cause a chain reaction to initiate the final explosive material or main charge. They can be either low or high explosive trains. Low explosive trains are something like a bullet - Primer and a propellant charge. High explosives trains can be more complex, either Two-Step (e.g. Detonator and Dynamite) or Three-Step (e.g. Detonator, Booster and ANFO).
Characteristics of Explosions
Explosive force is released at 90 degree angles from the surface of an explosive. If the surface is cut or shaped the explosive forces can be focused directionally, and will produce a greater effect. The following have been used: