Primary and secondary explosives

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Primary and secondary are the two distinct classifications of explosives.

A primary explosive is an explosive that is extremely sensitive to stimuli such as impact, friction, heat, or electrostatic sources of initiation. Two examples are lead azide and lead styphnate. They are often used in detonators or to trigger larger charges of less sensitive secondary explosives.

A secondary explosive is less sensitive and are therefore usable in a wider variety of applications. Examples of secondary explosives include TNT and RDX.

[edit] Primary explosives

As a very general rule, primary explosives are considered to be those compounds that are more sensitive than PETN. As a practical measure, primary explosives are sufficiently sensitive that they can be reliably initiated with a blow from a hammer; however, PETN can usually be initiated in this manner, so this is only a very broad guideline. Additionally, several compounds, such as nitrogen triiodide, are so sensitive that they cannot even be handled without detonating.

A number of primary explosives are commonly used in blasting caps to translate a signal (electrical, shock, or in the case of laser detonation systems, light) into an action, i.e., an explosion. A small quantity—usually milligrams—is sufficient to initiate a larger charge of explosive that is usually safer to handle.

Primary explosives include: