This is likely to make people forget that explosives are the basis for many of mankind's most constructive efforts. Explosives blast rocks and ores loose in mines and quarries. They also move great masses of earth and break coal into small pieces. A mechanical explosive depends on a physical reaction such as overloading a container with compressed air. Such a device has some application in mining, in which the release of gas from chemical explosives may be undesirable, but otherwise is very little used.
Chemical explosives account for virtually all explosive applications in engineering.
When an explosion occurs, a solid material of relatively small bulk is transformed into a large volume of hot gases in a fraction of a second. The explosive breaks down chemically, and a great quantity of heat is released. In an instant, oxygen reacts with other elements such as carbon and hydrogen. The lightning-like expansion of gases produces a shock wave that slams against surrounding surfaces and blasts objects from its path. Explosions are usually classified as combustion, or burning, type or detonation type.