An explosive undergoes a rapid chemical reaction producing gases, heat and pressure. Essential characteristics include producing gases rapidly in a self-sustaining reaction. Explosives are classified as low explosives which burn rapidly or high explosives which detonate. High explosives are further divided into primary explosives which are highly sensitive and secondary explosives which require more energy to detonate. Explosives have various applications including mining, construction and weapons. Common high explosives used are TNT, RDX, dynamite, C4 and tetryl.