Initiating Explosives
The primary safety considerations in the formulation, manufacture, and use of explosives are that they must never explode prematurely but always explode when desired. Often this balance is achieved with an insensitive main charge being initiated by the le
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The primary safety considerations in the formulation, manufacture, and use of explosives are that they must never explode prematurely but always explode when desired. Often this balance is achieved with an insensitive main charge being initiated by the least amount of a more sensitive explosive. This concept is expanded to that of an explosive train in which a series of decreasingly sensitive explosives is ultimately sufficient to initiate an insensitive main charge. The sensitivity of explosives to initiation provides a common means of classification: o
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Primary syn. initiator explosives, those most sensitive to heat, shock, electric spark, friction, and impact. They are usually high explosives such as the fulminates and lead azide, although lead azide may be sensitized with a small amount of lead styphnate. Secondary explosives, those that do not easily go from deflagration to detonation, do not initiate electrostatically with ease, and require larger shocks to detonate. They include nitrocellulose, PETN, and desensitized nitroglycerine. Tertiary explosives, those most difficult to detonate. They include extremely powerful high explosives like RDX and HMX.
Other explosives may be added to explosive trains to sensitize certain components or add a time delay. There are as many combinations as necessary to
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M. A. Fox, Glossary for the Worldwide Transportation of Dangerous Goods and Hazardous Materials © Springer-Verlag Berlin Heidelberg 1999
Initiating Explosives
marry the function, power, speed, reliability, timing, and safety of a system. Many of the terms used to describe initiating explosives and devices are used interchangeably and without precision. DETONATORS
Nonelectric Detonators In mining and demolition, high explosive charges are initiated by detonators in carefully timed sequences to minimize vibration and damage to surrounding structures and control rock breakage and throw. Detonators are devices that contain a few grams of explosive that are placed on, against, or into the main charge (a blasting agent). Introduced in the 1860s, the first detonators were called blasting caps or caps (names still used synonymously with detonator). They were capsules of mercury fulminate which initiated a charge of nitroglycerine. Mercury fulminate detonators were widely replaced due to their extreme sensitivity. Contemporary simple nonelectric detonators contain a small quantity of primary explosive (often lead azide) which, once ignited by a fuse, ignites the more powerful base charge of a secondary explosive (an additional low explosive may be used between the fuse and the primary explosive). Electric Detonators The introduction of bridgewire allowed blasting caps to be initiated electrically rather than by a fuse which greatly incre
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