ANNEX 18. The source and the manifestation of energy in the atomic bomb differ from those in conventional explosions. The energy stored in an explosive such as T.N.T. is chemical, and when liberated is used in the rapid conversion of the explosive to a gas. This gas, seeking to occupy a volume many times larger than did the solid explosive, exercises intense pressure on the surrounding air, which in turn passes it on to the next layer of air, and so on. The belt of high pressure thus rapidly moving outward from the explosion is the blast wave, and is the major cause of damage from high explosive.