This chapter has so far described the total chemical energy released when a chemical explosion takes place. This energy is released in the form of kinetic energy and heat over a very short time, i.e. microseconds. In a detonating explosive a supersonic wave is established near to the initiation point and travels through the medium of the explosive, sustained by the exothermic decomposition of the explosive material behind it. On reaching the periphery of the explosive material the detonation wave passes into the surrounding medium, and exerts on it a sudden, intense pressure, equivalent to a violent mechanical blow. If the medium is a solid, i.e. rock or stone, the violent mechanical blow will cause multiple cracks to form in the rock. This effect is known as brisance which is directly related to the detonation pressure in the shockwave front.

After the shockwave has moved away from the explosive composition the gaseous products begin to expand and act upon the surrounding medium. A crater will be formed if the medium is earth, in water a gas bubble is formed and in air a blast wave develops. The intensity of the gaseous expansion will depend upon the power ( Q V) of the explosive.

The pressure of explosion P _e is the maximum static pressure which may be achieved when a given weight of explosive is burned in a closed vessel of fixed volume. The pressure attained is so high...