How Explosions Work Explosions happen when certain chemical compounds undergo either chemical decomposition or combustion processes. The speed at which these chemical reactions occur is the primary defining factor in determining the explosive force that is generated As the reaction takes place the chemical bonds are broken which releases large amounts of energy in the form of heat. At the same time gases are formed from the chemical compounds and begin rapidly expanding. The speeds at which these reactions propagate commonly exceed 4000 meters per second. This speed is dependent upon the type of explosive used and the density of the explosive; it is called the velocity of detonation (VOD).