Detonator
[1] Detonators come in a variety of types, depending on how they are initiated (chemically, mechanically, or electrically) and details of their inner working, which often involve several stages.
[2] [3] The original electric detonators invented in 1875 independently by Julius Smith and Perry Gardiner used mercury fulminate as the primary explosive.
Around the turn of the century performance was enhanced in the Smith-Gardiner blasting cap by the addition of 10-20% potassium chlorate.
The first blasting cap or detonator was demonstrated in 1745 when British physician and apothecary William Watson showed that the electric spark of a friction machine could ignite black powder, by way of igniting a flammable substance mixed in with the black powder.
[5] In 1750, Benjamin Franklin in Philadelphia made a commercial blasting cap consisting of a paper tube full of black powder, with wires leading in both sides and wadding sealing up the ends.
When a strong current from a large battery (which he called a "deflagrator" or "calorimotor") was passed through the fine strand, it became incandescent and ignited the charge of gunpowder.
[16] Electric match caps were developed in the early 1900s in Germany, and spread to the US in the 1950s when ICI International purchased Atlas Powder Co.
Early blasting caps also used silver fulminate, but it has been replaced with cheaper and safer primary explosives.
In situations where nanosecond accuracy is required, specifically in the implosion charges in nuclear weapons, exploding-bridgewire detonators are employed.
A new development is a slapper detonator, which uses thin plates accelerated by an electrically exploded wire or foil to deliver the initial shock.
Non-electric detonators were invented by the Swedish company Nitro Nobel in the 1960s and 1970s, and launched to the demolitions market in 1973.
While currently expensive, wireless detonators can enable new mining techniques as multiple blasts can be loaded at once and fired in sequence without putting humans in harm's way.
An equivalent strength cap comprises 0.40-0.45 grams of PETN base charge pressed in an aluminum shell with bottom thickness not to exceed to 0.03 of an inch, to a specific gravity of not less than 1.4 g/cc, and primed with standard weights of primer depending on the manufacturer.
Some solid pack fuses incorporate a small pyrotechnic delay element, up to a few hundred milliseconds, before the cap fires.
Match type blasting caps use an electric match (insulating sheet with electrodes on both sides, a thin bridgewire soldered across the sides, all dipped in ignition and output mixes) to initiate the primary explosive, rather than direct contact between the bridgewire and the primary explosive.
[22][23] Slappers, instead of directly using the exploding foil to detonate the initiator explosive, use the electrical vaporization of the foil to drive a small circle of insulating material such as PET film or kapton down a circular hole in an additional disc of insulating material.
[22] Laser initiation of explosives, propellants or pyrotechnics has been attempted in three different ways, (1) direct interaction with the HE or Direct Optical Initiation (DOI); (2) rapid heating of a thin film in contact with a HE; and (3) ablating a thin metal foil to produce a high velocity flyer plate that impacts the HE (laser flyer).
