By Tom Harris
Explosives come in many different forms, from small grenade to huge thermonuclear warheads.
The fundamental concept behind explosives is simple. At the simplest level, an explosive is just something that burns or decomposes very rapidly, producing a lot of heat and gas in a short amount of time.
A typical explosive consists of an explosive material, a detonation device, and, usually, some sort of housing. The explosive material undergoes a rapid chemical reaction, either combustion or decomposition, which is triggered by heat or shock energy from the detonator.
In this chemical reaction, compounds break down to form gases. The reactants (the original chemical compounds) have a large amount of energy stored as chemical bonds between atoms. When the compound molecules break apart into their component atoms, the products (the resulting gases) might use some of this energy to form new bonds, but not all of it. The majority of the "leftover" energy takes the form of extreme heat.
These concentrated gases are under very high pressure, which causes rapid expansion. The heat speeds up the movement of individual gas particles, which boosts the pressure even more. In a high explosive, the gas pressure is powerful enough to destroy structures and injure or kill targets. If the gas expands faster than the speed of sound, it creates a very powerful shock wave. The pressure may also push fragments of solid material outward at great speed, causing them to hit people or structures with a lot of force.
In low explosives, such as the propellant in a bullet, the chemical reaction occurs relatively slowly and the pressure isn't as damaging; the explosion is meant only to propel a small object. High explosives, such as C-4 and TNT, expand far more rapidly, and generate much greater pressure. Explosives experts refer to rapid explosive reactions as detonation and slower explosive reactions as deflagration.
