Low Explosives and HighExplosives.

Low explosives are compounds where the rate of decomposition proceeds through the material at less than the speed of sound. The decomposition is propagated by a flame front (deflagration) which travels much more slowly through the explosive material than a shock wave of a high explosive. Under normal conditions, low explosives undergo deflagration at rates that vary from a few centimeters per second to approximately 400 metres per second. It is possible for them to deflagrate very quickly, producing an effect similar to a detonation. This can happen under higher pressure or temperature, which usually occurs when ignited in a confined space.
A low explosive is usually a mixture of a combustible substance and an oxidant that decomposes rapidly (deflagration); however, they burn more slowly than a high explosive, which has an extremely fast burn rate.
Low explosives are normally employed as propellants. Included in this group are gun powders and light pyrotechnics, such as flares and fireworks, but can replace high explosives in certain applications, see gas pressure blasting.

High explosives are explosive materials that detonate, meaning that the explosive shock front passes through the material at a supersonic speed. High explosives detonate with explosive velocity rates ranging from 3 to 9 km/s. They are normally employed in mining, demolition, and military applications. They can be divided into two explosives classes differentiated by sensitivity: primary explosive and secondary explosive. The term high explosive is in contrast to the term low explosive, which explodes (deflagrates) at a slower rate.

Causes of Explosion: Natural and Astronomical

Explosions can occur in nature. Most natural explosions arise from volcanic processes of various sorts. Explosive volcanic eruptions occur when magma rising from below has much dissolved gas in it; the reduction of pressure as the magma rises causes the gas to bubble out of solution, resulting in a rapid increase in volume. Explosions also occur as a result of impact events and in phenomena such as hydrothermal explosions (also due to volcanic processes). Explosions can also occur outside of Earth in the universe in events such as supernova. Explosions frequently occur during Bushfires in Eucalyptus forests where the volatile oils in the tree tops suddenly burst.


Animal bodies can also be explosive, as some animals hold a large amount of flammable material such as animal fat. This, in rare cases, results in naturally exploding animals.


Among the largest known explosions in the universe are supernovae, which result when a star explodes from the sudden starting or stopping of nuclear fusion, and gamma ray bursts, whose nature is still in some dispute. Solar flares are an example of explosion common on the Sun, and presumably on most other stars as well. The energy source for solar flare activity comes from the tangling of magnetic field lines resulting from the rotation of the Sun's conductive plasma. Another type of large astronomical explosion occurs when a very large meteoroid or an asteroid impacts the surface of another object, such as a planet.

United Nations Organization (UNO) Hazard Class and Division (HC/D)

The Hazard Class and Division (HC/D) is a numeric designator within a hazard class indicating the character, predominance of associated hazards, and potential for causing personnel casualties and property damage. It is an internationally accepted system that communicates using the minimum amount of markings the primary hazard associated with a substance.

 Explosives Warning Sign

Listed below are the Divisions for Class 1 (Explosives):

• 1.1 Mass Detonation Hazard. With HC/D 1.1, it is expected that if one item in a container or pallet inadvertently detonates, the explosion will sympathetically detonate the surrounding items. The explosion could propagate to all or the majority of the items stored together, causing a mass detonation. There will also be fragments from the item’s casing and/or structures in the blast area.
• 1.2 Non-mass explosion, fragment-producing. HC/D 1.2 is further divided into three subdivisions, HC/D 1.2.1, 1.2.2 and 1.2.3, to account for the magnitude of the effects of an explosion.
• 1.3 Mass fire, minor blast or fragment hazard. Propellants and many pyrotechnic items fall into this category. If one item in a package or stack initiates, it will usually propagate to the other items, creating a mass fire.
• 1.4 Moderate fire, no blast or fragment. HC/D 1.4 items are listed in the table as explosives with no significant hazard. Most small arms and some pyrotechnic items fall into this category. If the energetic material in these items inadvertently initiates, most of the energy and fragments will be contained within the storage structure or the item containers themselves.
• 1.5 mass detonation hazard, very insensitive.
• 1.6 detonation hazard without mass detonation hazard, extremely insensitive.

Explosion : Definition and History

An detonative material, well-known as an explosive, is a reactive compound that bears a large sum of potential energy that can bring about a blast whenever discharged abruptly, ordinarily followed by the yield of luminosity, thermal energy, sound, and pressure sensation. An explosive charge is a count of amount of unstable material.

This potential energy stacked in an explosive material may be chemical energy, specified glyceryl tri nitrate or grain dust supercharged compacted fluid, such as a gas piston chamber, aerosol container, or pyrotechnics.

Atomic energy, such as in the fissionable isotopes uranium-235 and plutonium-239

While ahead of time caloric weapon systems, for Grecian fire, have subsisted for old times, the first of all widely ill-used detonative in war and excavation was black powder, made up in 9th century China. This stuff was highly sensitive to body of water, and developed lots of dark smoke. The firstly valuable explosive more inviolable than black powder was tri nitroglycerin, formulated in 1847. Since nitroglycerin was volatile, it was put back by cellulose nitrate, smoke-free powder, dynamite and gelignite (the two latter manufactured by Alfred Bernhard Nobel). Second World War projected a far-reaching application of new explosives. Successively, these have for the most part been replaced by advanced explosives such as TNT and C-4.

The increased availability of chemicals has granted the construction of improvised explosive devices.