TABLE OF CONTENTS In most situations an event by a chemical explosive can be divided into four stages: these are ignition, the growth of deflagration, the transition from deflagration to detonation, and the propagation of detonation. In some circumstances ignition can lead straight to detonation. This only occurs when the initial stimulus is able to generate a large quantity of energy in the explosive composition. Heat is then produced by adiabatic compression in the shockwave front which results in detonation. Ignition to detonation only takes place in specially-formulated explosive compositions and requires special conditions and very high pressures.
Ignition occurs when part of a combustible material such as an explosive is heated to or above its ignition temperature. The ignition temperature is the minimum temperature required for the process of initiation to be self-sustaining.
Explosive materials are ignited by the action of an external stimulus which effectively inputs energy into the explosive and raises its temperature. The external stimulus can be friction, percussion, electrical impulse, heat, etc. Once stimulated the rise in temperature of the explosive causes a sequence of pre-ignition reactions to commence. These involve transitions in the crystalline structure, liquid phases changing into gaseous phases, and thermal decomposition of one or more of the ingredients. These reactions then lead to a self-sustaining combustion of the material, i.e. ignition. As the temperature rises, the rate of the heat produced increases exponentially whereas the rate of heat lost is linear. Ignition occurs at the temperature where the rate of heat...
