Detonator

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Top: small nonel detonator with 2 ms delay for chaining nonel tubes; middle: class B SPD detonator; bottom: class C SPD detonator Detonator.jpg
Top: small nonel detonator with 2 ms delay for chaining nonel tubes; middle: class B SPD detonator; bottom: class C SPD detonator
Inserting detonators into blocks of C-4 explosive Eod2.jpg
Inserting detonators into blocks of C-4 explosive

A detonator, frequently a blasting cap, is a device used to trigger an explosive device. Detonators can be chemically, mechanically, or electrically initiated, the last two being the most common.

Contents

The commercial use of explosives uses electrical detonators or the capped fuse which is a length of safety fuse to which an ordinary detonator has been joined. Many detonators' primary explosive is a material called ASA compound. This compound is formed from lead azide, lead styphnate and aluminium and is pressed into place above the base charge, usually TNT or tetryl in military detonators and PETN in commercial detonators.

Other materials such as DDNP (diazo dinitro phenol) are also used as the primary charge to reduce the amount of lead emitted into the atmosphere by mining and quarrying operations. Old detonators used mercury fulminate as the primary, often mixed with potassium chlorate to yield better performance.

A blasting cap is a small sensitive primary explosive device generally used to detonate a larger, more powerful and less sensitive secondary explosive such as TNT, dynamite, or plastic explosive.

Blasting caps come in a variety of types, including non-electric caps, electric caps, and fuse caps. They are used in commercial mining, excavation, and demolition. Electric types are set off by a short burst of current sent by a blasting machine via a long wire to the cap to ensure safety. Traditional fuse caps have a fuse which is ignited by a flame source, such as a match or a lighter.

Need for detonators

The need for detonators such as blasting caps came from the development of safer explosives. Different explosives require different amounts of energy (their activation energy) to detonate. Most commercial explosives are formulated with a high activation energy, to make them stable and safe to handle so they will not explode if accidentally dropped, mishandled, or exposed to fire. These are called secondary explosives. However they are correspondingly difficult to detonate intentionally, and require a small initiating explosion. This is provided by a detonator.

A detonator contains an easy-to-ignite primary explosive that provides the initial activation energy to start the detonation in the main charge. Explosives commonly used in detonators include mercury fulminate, lead azide, lead styphnate, tetryl, and DDNP. Blasting caps and some detonators are stored separately and not inserted into the main explosive charge until just before use, keeping the main charge safe. Early blasting caps also used silver fulminate, but it has been replaced with cheaper and safer primary explosives. Silver azide is still used sometimes, but very rarely due to its high price.

Detonators are hazardous for untrained personnel to handle since they contain primary explosive. They are sometimes not recognized as explosives due to their appearance, leading to injuries.

Types

Ordinary detonators

Ordinary detonators usually take the form of ignition-based explosives. While they are mainly used in commercial operations, ordinary detonators are still used in military operations. This form of detonator is most commonly initiated using a safety fuse, and used in non time-critical detonations e.g. conventional munitions disposal. Well known detonators are lead azide [Pb(N3)2], silver azide [AgN3] and mercury fulminate [Hg(ONC)2].

Electrical detonators

There are three categories of electrical detonators: instantaneous electrical detonators (IED), short period delay detonators (SPD) and long period delay detonators (LPD). SPDs are measured in milliseconds and LPDs are measured in seconds. In situations where nanosecond accuracy is required, specifically in the implosion charges in nuclear weapons, exploding-bridgewire detonators are employed. The initial shock wave is created by vaporizing a length of a thin wire by an electric discharge. A new development is a slapper detonator, which uses thin plates accelerated by an electrically exploded wire or foil to deliver the initial shock. It is in use in some modern weapons systems. A variant of this concept is used in mining operations, when the foil is exploded by a laser pulse delivered to the foil by optical fiber.

Non-electric detonators

A non-electric detonator is a shock tube detonator designed to initiate explosions, generally for the purpose of demolition of buildings and for use in the blasting of rock in mines and quarries. Instead of electric wires, a hollow plastic tube delivers the firing impulse to the detonator, making it immune to most of the hazards associated with stray electric current. It consists of a small diameter, three-layer plastic tube coated on the innermost wall with a reactive explosive compound, which, when ignited, propagates a low energy signal, similar to a dust explosion. The reaction travels at approximately 6,500 ft/s (2,000 m/s) along the length of the tubing with minimal disturbance outside of the tube. Non-electric detonators were invented by the Swedish company Nitro Nobel in the 1960s and 1970s, and launched to the demolitions market in 1973.

Electronic detonators

In civil mining, electronic detonators have a better precision for delays. Electronic detonators are designed to provide the precise control necessary to produce accurate and consistent blasting results in a variety of blasting applications in the mining, quarrying, and construction industries. Electronic detonators may be programmed in millisecond or sub-millisecond increments using a dedicated programming device.

Wireless detonators

Wireless electronic detonators are beginning to be available in the civil mining market. [1] Encrypted radio signals are used to communicate the blast signal to each detonator at the correct time. 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.

Number 8 blasting caps

A number 8 test blasting cap is one containing 2 grams of a mixture of 80 percent mercury fulminate and 20 percent potassium chlorate, or a blasting cap of equivalent strength. 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.

Types of blasting caps

Cutaway diagram of various types of blasting caps and detonators.svg

Pyrotechnic fuse blasting cap

The oldest and simplest type of cap, fuse caps are a metal cylinder, closed at one end. From the open end inwards, there is first an empty space into which a pyrotechnic fuse is inserted and crimped, then a pyrotechnic ignition mix, a primary explosive, and then the main detonating explosive charge.

The primary hazard of pyrotechnic blasting caps is that for proper usage, the fuse must be inserted and then crimped into place by crushing the base of the cap around the fuse. If the tool used to crimp the cap is used too close to the explosives, the primary explosive compound can detonate during crimping. A common hazardous practice is crimping caps with one's teeth; an accidental detonation can cause serious injury to the mouth.

Fuse type blasting caps are still in active use today. They are the safest type to use around certain types of electromagnetic interference, and they have a built in time delay as the fuse burns down.

Solid pack electric blasting cap

Solid pack electric blasting caps use a thin bridgewire in direct contact (hence solid pack) with a primary explosive, which is heated by electric current and causes the detonation of the primary explosive. That primary explosive then detonates a larger charge of secondary explosive.

Some solid pack fuses incorporate a small pyrotechnic delay element, up to a few hundred milliseconds, before the cap fires.

Match or fusehead electric blasting cap

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. The match can be manufactured separately from the rest of the cap and only assembled at the end of the process.

Match type caps are now the most common type found worldwide.

Exploding bridgewire detonator or blasting cap

This type of detonator was invented in the 1940s as part of the Manhattan Project to develop nuclear weapons. The design goal was to produce a detonator which acted very rapidly and predictably. Both Match and Solid Pack type electric caps take a few milliseconds to fire, as the bridgewire heats up and heats the explosive to the point of detonation. Explosive bridgewire or EBW detonators use a higher voltage electric charge and a very thin bridgewire, .04 inch long, .0016 diameter, (1 mm long, 0.04 mm diameter). Instead of heating up the explosive, the EBW detonator wire is heated so quickly by the high firing current that the wire actually vaporizes and explodes due to electric resistance heating. That electrically driven explosion then fires the detonator's initiator explosive (usually PETN).

Some similar detonators use a thin metal foil instead of a wire, but operate in the same manner as true bridgewire detonators.

In addition to firing very quickly when properly activated, EBW detonators are safe from stray static electricity and other electric current. Enough current and the bridgewire may melt, but it is small enough that it cannot detonate the initiator explosive unless the full high-voltage high-current charge passes through the bridgewire. EBW detonators are used in many civilian applications where radio signals, static electricity, or other electrical hazards might cause accidents with conventional electric detonators.

Slapper detonator or blasting cap

Slapper detonators are an improvement on EBW detonators. 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. At the far end of that hole is a pellet of conventional initiator explosive.

The conversion efficiency of energy from electricity into kinetic energy of the flying disk or slapper can be 20–40%.

Since the slapper impacts a wide area - 40 thousandths of an inch (roughly one mm) across - of the explosive, rather than a thin line or point as in an exploding foil or bridgewire detonator, the detonation is more regular and requires less energy. Reliable detonation requires raising a minimum volume of explosive to temperatures and pressures at which detonation starts. If energy is deposited at a single point, it can radiate away in the explosive in all directions in rarefaction or expansion waves, and only a small volume is efficiently heated or compressed. The flier disc loses impact energy at its sides to rarefaction waves, but a conical volume of explosive is efficiently shock compressed.

Slapper detonators are used in nuclear weapons. These components require large quantities of energy to initiate, making them extremely unlikely to accidentally discharge.

Laser ordnance initiators

In this type, a pulse from a laser passes down an optical fiber to strike and thus initiate a carbon-doped explosive. These initiators are highly reliable. Unintentional initiation is very difficult as the explosive can only be detonated by the attached laser, which is precisely tuned to do so, or a completely independent laser that matches.

History

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. [2]

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. The two wires came close but did not touch, so a large electric spark discharge between the two wires would fire the cap. [3]

In 1832, a hot wire detonator was produced by American chemist Robert Hare, although attempts along similar lines had earlier been attempted by the Italians Volta and Cavallo. [4] Hare constructed his blasting cap by passing a multistrand wire through a charge of gunpowder inside a tin tube; he had cut all but one fine strand of the multistrand wire so that the fine strand would serve as the hot bridgewire. 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. [5] [6]

In 1863, Alfred Nobel realized that although nitroglycerin could not be detonated by a fuse, it could be detonated by the explosion of a small charge of gunpowder, which in turn was ignited by a fuse. [7] Within a year, he was adding mercury fulminate to the gunpowder charges of his detonators, and by 1867 he was using small copper capsules of mercury fulminate, triggered by a fuse, to detonate nitroglycerin. [8]

In 1868, Henry Julius Smith of Boston introduced a cap that combined a spark gap ignitor and mercury fulminate, the first electric cap able to detonate dynamite. [9]

In 1875, Smith—and then in 1887, Perry G. Gardner of North Adams, Massachusetts—developed electric detonators that combined a hot wire detonator with mercury fulminate explosive. [10] [11] [12] These were the first generally modern type blasting caps. Modern caps use different explosives and separate primary and secondary explosive charges, but are generally very similar to the Gardner and Smith caps.

Smith also invented the first satisfactory portable power supply for igniting blasting caps: a high-voltage magneto that was driven by a rack and pinion, which in turn was driven by a T-handle that was pushed downwards. [13]

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. These match caps have become the predominant world standard cap type.

Fictional variations

See also

Related Research Articles

Dynamite Explosive made using nitroglycerin

Dynamite is an explosive made of nitroglycerin, sorbents and stabilizers. It was invented by the Swedish chemist and engineer Alfred Nobel in Geesthacht, Northern Germany and patented in 1867. It rapidly gained wide-scale use as a more powerful alternative to black powder.

Explosive Substance that can explode

An explosive is a reactive substance that 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, which may either be composed solely of one ingredient or be a mixture containing at least two substances.

Pentaerythritol tetranitrate Chemical compound

Pentaerythritol tetranitrate (PETN), also known as PENT, PENTA, TEN, corpent, or penthrite, is an explosive material. It is the nitrate ester of pentaerythritol, and is structurally very similar to nitroglycerin. Penta refers to the five carbon atoms of the neopentane skeleton. PETN is a powerful explosive material with a relative effectiveness factor of 1.66. When mixed with a plasticizer, PETN forms a plastic explosive. Along with RDX it is the main ingredient of Semtex.

Mercury(II) fulminate Chemical compound

Mercury(II) fulminate, or Hg(CNO)2, is a primary explosive. It is highly sensitive to friction, heat and shock and is mainly used as a trigger for other explosives in percussion caps and detonators. Mercury(II) cyanate, though its chemical formula is identical, has a different atomic arrangement; the cyanate and fulminate anions are isomers.

Percussion cap Ignition source in a type of firearm mechanism

The percussion cap or percussion primer, introduced in the early 1820s, is a type of single-use percussion ignition device for muzzle loader firearm locks enabling them to fire reliably in any weather condition. This crucial invention gave rise to the cap lock mechanism or percussion lock system using percussion caps struck by the hammer to set off the gunpowder charge in percussion guns including percussion rifles and cap and ball firearms. Any firearm using a caplock mechanism is a percussion gun. Any long gun with a cap-lock mechanism and rifled barrel is a percussion rifle. Cap and ball describes cap-lock firearms discharging a single bore-diameter spherical bullet with each shot.

Exploding-bridgewire detonator Detonator fired by electric current

The exploding-bridgewire detonator is a type of detonator used to initiate the detonation reaction in explosive materials, similar to a blasting cap because it is fired using an electric current. EBWs use a different physical mechanism than blasting caps, using more electricity delivered much more rapidly, and explode in a much more precise timing after the electric current is applied, by the process of exploding wire method. This has led to their common use in nuclear weapons.

A triggering sequence, also called an explosive train, is a sequence of events that culminates in the detonation of explosives. For safety reasons, most widely used high explosives are difficult to detonate. A primary explosive of higher sensitivity is used to trigger a uniform and predictable detonation of the main body of the explosive. Although the primary explosive itself is generally a more sensitive and expensive compound, it is only used in small quantities and in relatively safely packaged forms. By design there are low explosives and high explosives made such that the low explosives are highly sensitive and high explosives are comparatively insensitive. This not only affords inherent safety to the usage of explosives during handling and transport, but also necessitates an explosive triggering sequence or explosive train. The explosive triggering sequence or the explosive train essentially consists of an 'initiator', an 'intermediary' and the 'high explosive'.

Fuse (explosives)

In an explosive, pyrotechnic device, or military munition, a fuse is the part of the device that initiates function. In common usage, the word fuse is used indiscriminately. However, when being specific, the term fuse describes a simple pyrotechnic initiating device, like the cord on a firecracker whereas the term fuze is sometimes used when referring to a more sophisticated ignition device incorporating mechanical and/or electronic components, such as a proximity fuze for an M107 artillery shell, magnetic or acoustic fuze on a sea mine, spring-loaded grenade fuze, pencil detonator, or anti-handling device.

Slapper detonator Type of electrically fired detonator

A slapper detonator, also called exploding foil initiator (EFI), is a relatively recent kind of a detonator developed by Lawrence Livermore National Laboratory, US Patent No. 4,788,913. It is an improvement of the earlier exploding-bridgewire detonator; instead of directly coupling the shock wave from the exploding wire, the expanding plasma from an explosion of a metal foil drives another thin plastic or metal foil called a "flyer" or a "slapper" across a gap, and its high-velocity impact on the explosive then delivers the energy and shock needed to initiate a detonation. Normally all the slapper's kinetic energy is supplied only by the heating of the plasma by the current passing through it, though constructions with a "back strap" to further drive the plasma forward by magnetic field exist too. This assembly is quite efficient; up to 30% of the electrical energy can be converted to the slapper's kinetic energy.

Hexamethylene triperoxide diamine Chemical compound

Hexamethylene triperoxide diamine (HMTD) is a high explosive organic compound. HMTD is an organic peroxide, a heterocyclic compound with a cage-like structure. It is a primary explosive. It has been considered as an initiating explosive for blasting caps in the early part of 20th century, mostly because of its high initiating power and its inexpensive production. As such, it was quickly taken up as a primary explosive in mining applications. However, it has since been superseded by more (chemically) stable compounds such as dextrinated lead azide and DDNP. HMTD is widely used in amateur made blasting caps.

A pyrotechnic fastener is a fastener, usually a nut or bolt, that incorporates a pyrotechnic charge that can be initiated remotely. One or more explosive charges embedded within the bolt are typically activated by an electric current, and the charge breaks the bolt into two or more pieces. The bolt is typically scored around its circumference at the point(s) where the severance should occur. Such bolts are often used in space applications to ensure separation between rocket stages, because they are lighter and much more reliable than mechanical latches.

Pencil detonator

A pencil detonator or time pencil is a time fuze designed to be connected to a detonator or short length of safety fuse. They are about the same size and shape as a pencil, hence the name. They were introduced during World War II and developed at Aston House, Hertfordshire, UK.

Electric match Device using electricity to ignite a combustible compound

An electric match is a device that uses an externally applied electric current to ignite a combustible compound.

A pyrotechnic initiator is a device containing a pyrotechnic composition used primarily to ignite other, more difficult-to-ignite materials, e.g. thermites, gas generators, and solid-fuel rockets. The name is often used also for the compositions themselves.

A bridgewire or bridge wire, also known as a hot bridge wire (HBW), is a relatively thin resistance wire used to set off a pyrotechnic composition serving as pyrotechnic initiator. By passing of electric current it is heated to a high temperature that starts the exothermic chemical reaction of the attached composition. After successful firing, the bridgewire melts, resulting in an open circuit.

Flash-lamp

The electric flash-lamp uses electric current to start flash powder burning, to provide a brief sudden burst of bright light. It was principally used for flash photography in the early 20th century but had other uses as well. Previously, photographers' flash powder, introduced in 1887 by Adolf Miethe and Johannes Gaedicke, had to be ignited manually, exposing the user to greater risk.

The safety fuse is a type of fuse invented and patented by English inventor William Bickford in 1831. Originally it consisted of a "tube" of gunpowder surrounded by a waterproofed varnished jute "rope." It replaced earlier and less reliable methods of igniting gunpowder blasting charges which had caused many injuries and deaths in the mining industry. The safety fuse burns at a rate of typically about 30 seconds per foot.

A shock tube detonator is a non-electric explosive fuze or initiator in the form of small-diameter hollow plastic tubing used to transport an initiating signal to an explosive by means of a shock wave traveling the length of the tube. Shock tube is used to convey a detonation signal to a detonator. Shock tube is a hollow extruded tube containing a thin layer of energetic material upon its inner diameter. Once it is initiated, the shock tube transfers a signal to a detonating output charge.

A contact fuze, impact fuze, percussion fuze or direct-action (D.A.) fuze (UK) is the fuze that is placed in the nose of a bomb or shell so that it will detonate on contact with a hard surface.

In firearms and artillery, the primer is the chemical and/or device responsible for initiating the propellant combustion that will push the projectiles out of the gun barrel.

References

  1. "Improving safety and productivity". www.oricaminingservices.com. Retrieved 2019-05-16.
  2. Watson, William (1744). "Experiments and observations tending to illustrate the nature and properties of electricity". Philosophical Transactions of the Royal Society of London. 43: 481–501. doi: 10.1098/rstl.1744.0094 . From p. 500: "But I can, at pleasure, fire gunpowder, and even discharge a musket, by the power of electricity, when the gunpowder has been ground with a little camphor, or with a few drops of some inflammable chemical oil."
  3. Franklin, Benjamin, Experiments and Observations on Electricity at Philadelphia in America (London, England: Francis Newberg, 1769), p. 92. From p. 92: "A small cartridge is filled with dry powder, hard rammed, so as to bruise some of the grains; two pointed wires are then thrust in, one at each end, the points approaching each other in the middle of the cartridge till within the distance of half an inch [1.27 cm]; then, the cartridge being placed in the circle [i.e., circuit], when the four [Leyden] jars are discharged, the electric flame leaping from the point of one wire to the point of the other, within the cartridge amongst the powder, fires it, and the explosion of the powder is at the same instant with the crack of the discharge."
  4. "Standing Well Back - Home - Inventing detonators". www.standingwellback.com. Retrieved 22 March 2018.
  5. Hare, Robert (1832) "Application of galvanism to the blasting of rocks," The Mechanics' Magazine , 17: 266–267.
  6. Note: Robert Hare had constructed his large battery (or "deflagrator" or "calorimotor", as he called it) in 1821. See: Hare, R. (1821) "A memoir on some new modifications of galvanic apparatus, with observations in support of his new theory of galvanism," The American Journal of Science and Arts, 3: 105–117.
  7. Patent for nitroglycerin: Nobel, A., British patent no. 1,813 (July 20, 1864).
  8. See:
    • Patent for dynamite: Nobel, Alfred, English patent no. 1,345 (May 7, 1867).
    • Nobel, Alfred, "Improved explosive compound", U.S. patent no. 78,317 (May 26, 1868). (See p. 2 for the description of the "percussion-cap".)
    • de Mosenthal, Henry (1899) "The life-work of Alfred Nobel," Journal of the Society of Chemical Industry, 18: 443–451; see p. 444.
  9. Smith, Henry Julius, "Improvement in electric fuses," U.S. Patent no. 79,268 (June 23, 1868).
  10. Cooper, Paul W., Explosives Engineering (New York, New York: Wiley-VHC, 1996), p. 339.
  11. See:
  12. Gardner, Perry G., "Electric fuse," U.S. Patent no. 377,851 (February 14, 1888).
  13. See:

Further reading