Explosives are chemicals and must be treated safely. They are highly reactive in nature. Explosives contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An explosive charge is a measured quantity of explosive material. The potential energy in explosives come from chemical energy, pressurized compressed gas or nuclear energy. Most commercial explosives have detonation velocities. The potential energy stored in an explosive material may be chemical energy (such as nitroglycerine), pressurized compressed gas (such as gas cylinder or aerosol), or nuclear (such as fissile isotopes of uranium-235).
Explosives can be basically classified into 2 categories: low explosives and high explosives. Low explosives burn at a slower rate and create less pressure compared to high explosives. Low explosives are normally used as propellants to send a rocket into space or force a bullet out of a gun. On the other hand, chemicals that explode faster than the speed of sound are said to be high explosives. Explosives are also categorized according to their sensitivity. Sensitive materials that can be exploded by a relatively small amount of heat or pressure are primary explosives and materials that remain relatively insensitive are secondary explosives.
Low explosives have combustible substances, an oxidant that burns (deflagrates) at speeds ranging from a few cm/sec to 400 m/sec, but usually on the lower end of that scale. Low explosives work the same way as burning wood or coal. Low explosives combine together a combustible substance and an oxidant at sufficient temperature releasing heat and rapidly expanding gases. Depending on the amount of oxygen in the surrounding, the deflagration with more or less speed and violence. At the higher levels, deflagrations resemble detonations. For many years, black powder was the most common low explosive used throughout the world. Black powder is also known as the gun powder. Black powder produced a large amount of smoke and was dangerous to use. Still, it is used for pyrotechnics (fireworks), special effects, and other specialized work, but it has been replaced in commercial blasting by safer, more productive explosive materials.
High explosives burn more rapidly and create more pressure compared to low explosives. They detonate instantaneously. There are many reaction sequences involved in a detonation process. It involves combination of a metal with chlorine releasing excess energy in the process. Other reactant combinations may include hydrogen with chlorine, metal with oxygen, hydrogen with oxygen, carbon with oxygen, oxygen with carbon monoxide, and nitrogen with hydrogen. In any explosive, one or many of these reactions may occur releasing large energy levels. Nitroglycerine was the first high explosive used in commercial blasting. It was known as "blasting oil." Nitroglycerine is dangerous to use because it is an unstable chemical. But in the late 1800’s, Alfred Nobel invented dynamite. Dynamite is a mixture of nitroglycerine with special clay, called kieselghur. He packed this mixture into sticks. Dynamite is the first high explosive that is safe. It does not accidentally explode if it is dropped, hammered or burned.
The standard qualities a compound or mixture must possess to qualify as an explosive include:
Rapid expansion of gases.
Generation of heat due to the exothermic reaction.
When ignited, explosives can be controlled in terms of rapidity and initiation of the reaction.
Explosives must have limited amount of toxicity.