Detonation and Combustion
The release of energy (energy extremely useful for military purposes) is fundamental to both these phenomena. In both detonation and combustion, energy is released when a complex molecule is broken down into simpler constituent parts; however, as will be explained below, combustion is a much slower process. Low explosives (like black powder) rely on combustion to generate energy.
Combustion is produced by the reaction of oxygen and some sort of fuel at high temperatures. As a result, the rate of a combustion reaction is limited both by the amount of fuel present and the amount of oxygen it comes in contact with. If the reaction had to rely on oxygen gathered from the surrounding atmosphere, it would be very slow. Instead, most low explosives include both a fuel and an oxidizing agent which releases oxygen when heated.
Consider for instance black powder, the most primitive form of gunpowder and the quintessential low explosive. In black powder, charcoal and sulphur are the fuel, and postassium nitrate (KNO3) is the oxidizing agent.
Detonation (A Regular Bomb)
Detonation is a process of intramolecular breakdown. It relies only on the presence of a single, suitable explosive material and enough energy to stimulate that breakdown. For instance, Octanitrocubane (a recently developed US Army explosive) releases a great deal of energy when its highly strained carbon-carbon bonds break apart in response to a shockwave. Because high explosives do not require oxygen (or any other co-reactant), they break down much more rapidly and are much more versatile than combustible materials.
High explosives generally cannot be detonated by heat alone and so require a detonator to deliver either a shock wave or an electric charge. The first high explosive, nitroglycerine, was packaged with its detonator as dynamite. Dynamite is detonated by lighting a simple cord fuse, which carries a flame to a small cap of low explosive black powder; the ignition of the black powder causes a shockwave to propagate through the nitroglycerine—initiating detonation.
Other high explosives of note:
· Picric Acid – First military high explosive, demonstrated by France in 1885. Notoriously volatile and difficult to handle.
· TNT – Developed by Alfred Nobel in 1860s, first used in a military application in 1902 (by Germany). TNT is extremely easy to handle in the manufacturing process; it was widely used throughout World War I.
· RDX – Developed by the British in 1899, but not put into service until after World War I. The acronym stands for “Research Department Explosive.” RDX is as easy to handle as TNT, but has a much greater explosive yield.
Firebombs combine high explosive and incendiary effects. High explosives release a great deal of energy over a broad area, in firebombs they also release a large quantity of extremely flammable material (gelled-fuel mixtures, magnesium, white phosphorus, etc.) which immediately bursts into flame. The aim of a firebomb is, obviously, to start a fire in an explosive manner. As a result, firebombs are often more effective at destroying a target than simple explosives alone; whatever is not blown apart by the initial detonation can be consumed by the ensuing fire.
Firebombs can also have further destructive effects:
- In underground installations and sealed bunkers, the fire rapidly consumes all available oxygen—suffocating any potential enemy survivors.
- The presence of active fires diverts enemy resources to extinguishing them, and makes it more difficult for the enemy to maneuver, communicate, and collect reconnaissance in and around the bombing site.
- During large-scale firebomb attacks, a massive conflagration creates an upward air current (by virtue of convection) which causes air to rush in towards the fire from all sides; this rapidly circulating air provides the fire with quantities of fresh oxygen, increasing the size of the fire and, in turn, the speed of the air current. This positive feedback loop (generally known as a fire storm) creates extremely large and intense fires.