How do Explosives Work?

Michael Anissimov

There are two types of explosives: low explosives such as gunpowder, and high explosives such as TNT. Low explosives generally are a mix of a combustible substance and an oxidant that burns (deflagrates) at speeds from between a few cm/sec to 400 m/sec, but usually on the lower end of that scale. High explosives are chemical compounds (one type of molecule) rather than a duo – these detonate rather than deflagrate, producing a supersonic shock wave of 1,000 - 9,000 m/sec.

Gunpowder is featured in explosives.
Gunpowder is featured in explosives.

Low explosives work the same way as burning wood or coal does: by combining together a combustible substance with an oxidant at sufficient temperature, heat and rapidly expanding gases are created. Depending on the level of oxygen in the surrounding medium, the deflagration occurs with more or less speed and violence. At the higher levels, deflagrations resemble detonations.

High explosives are chemically unstable compounds, often including several nitrate groups. When exposed to sufficient heat or mechanical shock, high explosives abruptly rearrange their molecular structure, deteriorating into reaction products and releasing much energy in the process.

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There are nine primary reaction sequences making up parts of the detonation process of high explosives, referred to as priorities. For instance, Priority 1 involves the combination of a metal with chlorine, releasing excess energy in the process. Other priorities include the combination of hydrogen with chlorine, a metal with oxygen, carbon and oxygen, hydrogen and oxygen, carbon monoxide and oxygen, nitrogen with itself, oxygen with itself, and hydrogen with itself. In any given explosive, several of these reactions may occur, each releasing large amounts of energy.

Because some explosives require extreme heat to detonate, explosive chains must be set up, where one lower-energy explosive is detonated by a blaster cap, which then provides the basis for the explosion of an additional substance.

Four standard qualities a compound or mixture must possess to be qualified as an explosive include the rapid expansion of gases, generation of heat (exothermic reaction), the rapidity of reaction, and the initiation of reaction, meaning that the explosive can be ignited in a controlled fashion. Another desirable quality for explosives for practical uses is a limited amount of toxicity.

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Discussion Comments


It's the sudden, extreme expansion that causes so much devastation.

For instance, a quantity of about 28 grams of nitrogen gas will take up 24.5 litres of space when the temperature is about 20 degrees celsius, and the pressure is normal.

In a small bomb, no bigger than a soft-drink bottle, you could pack up to a kilo of explosives, and when taking into account how much space that could take up if it expanded sufficiently fast, it's easy to realize that it'd create a massive shock-wave as it releases it's energy.

Added to the fact that humans can only stand so much force, and when you've got gas slamming every inch of your skin with the force of a sledgehammer, your skeleton, protective clothing and organs won't stand much of chance.

It's saddening that we should use such fantastic knowledge to cause such a horrific effect.


metal fragments are not required in explosives. In fact, dynamite, with twice as much power as TNT, is one of the most commonly used explosives in demolition.


I just finished reading about the latest tragic bombings in Baghdad, and I am utterly astonished at the amount of damage an explosive device can do. I simply do not understand how explosives that don't contain metal fragments can do the kind of damage that these things do. Is it simply due to the expansive power of gases or am i missing something here?

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