Blasting cap
Encyclopedia
Sensitivity (explosives)
Sensitivity of explosives is the degree to which an explosive can be initiated by impact, heat, or friction.Sensitivity, along with stability and brisance are three of the most significant properties of explosives that affect their use and application. All explosive compounds have a certain amount...
primary explosive device generally used to detonate
Detonator
A detonator is a device used to trigger an explosive device. Detonators can be chemically, mechanically, or electrically initiated, the latter two being the most common....
a larger, more powerful and less sensitive secondary explosive such as TNT, dynamite
Dynamite
Dynamite is an explosive material based on nitroglycerin, initially using diatomaceous earth , or another absorbent substance such as powdered shells, clay, sawdust, or wood pulp. Dynamites using organic materials such as sawdust are less stable and such use has been generally discontinued...
, or plastic explosive
Plastic explosive
Plastic explosive is a specialised form of explosive material. It is a soft and hand moldable solid material. Plastic explosives are properly known as putty explosives within the field of explosives engineering....
.
Blasting caps come in a variety of types, some of which are: non-electric caps, electric caps, and fuse caps. They are used in commercial mining
Mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...
, excavation, and demolition
Demolition
Demolition is the tearing-down of buildings and other structures, the opposite of construction. Demolition contrasts with deconstruction, which involves taking a building apart while carefully preserving valuable elements for re-use....
. Electric types are set off by a short burst of current conducted by a long wire to the cap to ensure safety. Traditional fuse caps have a fuse which is lit by a match.
The need for blasting caps arises from sensitivity
Sensitivity (explosives)
Sensitivity of explosives is the degree to which an explosive can be initiated by impact, heat, or friction.Sensitivity, along with stability and brisance are three of the most significant properties of explosives that affect their use and application. All explosive compounds have a certain amount...
issues of an explosive compound. All explosive compounds require a certain amount of energy to detonate. If an explosive is too sensitive, it may go off unexpectedly, so most commercial explosives are formulated to be stable and safe to handle and will not explode if accidentally dropped, mishandled, or exposed to fire. However, such explosives (called secondary explosives) are hard to detonate intentionally as well. A blasting cap contains an easy-to-ignite explosive that provides the initial activation energy
Activation energy
In chemistry, activation energy is a term introduced in 1889 by the Swedish scientist Svante Arrhenius that is defined as the energy that must be overcome in order for a chemical reaction to occur. Activation energy may also be defined as the minimum energy required to start a chemical reaction...
to start a detonation in a more stable explosive. The blasting cap is stored separately and not inserted into the main explosive charge until just before use, keeping the main charge safe.
Most blasting caps contain what is called a primary explosive, which is a high explosive compound that will explode from flame, heat or shock. A blasting cap may also contain a booster
Explosive booster
An explosive booster acts as a bridge between a low energy explosive and a low sensitivity explosive such as TNT. It increases the explosive shockwave from an initiating explosive to the degree sufficient to detonate the secondary charge.Unlike C4 plastic explosive, not all explosives can be...
, another less sensitive but more energetic explosive that makes the cap more powerful, and thus more reliable for detonating secondary explosives.
Explosives commonly used in blasting caps include mercury fulminate, lead azide, lead styphnate
Lead styphnate
Lead styphnate , whose name is derived from styphnic acid, is an explosive used as a component in primer and detonator mixtures for less sensitive secondary explosives....
and tetryl
Tetryl
2,4,6-Trinitrophenylmethylnitramine commonly referred to as tetryl is a sensitive explosive compound used to make detonators and explosive booster charges....
.
The recommended primary explosive is DDNP because it is non toxic, easy to make and not too sensitive.
Because they contain easy-to-detonate primary explosives, blasting caps are hazardous for untrained personnel to handle. They are sometimes not recognized as explosives due to their appearance, leading to injuries.
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 wounds to the mouth. Proper recommended procedure is to position the crimping tool and tighten it up, then hold it behind oneself slightly below waist level while actually crimping. While embarrassing, injuries are not serious.
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 bridgewireBridgewire
A bridgewire, bridge wire, or hot bridge wire 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...
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 matchElectric match
An electric match is a device that uses an externally applied electric current to ignite a combustible compound.-Use:Electric matches can be used in any application where source of heat is needed at a precisely controlled point in time, typically to ignite a propellant or explosive...
(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 projectManhattan Project
The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...
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 (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 electrical driven explosion then fires the detonator's initiator explosive (usually PETN
PETN
Pentaerythritol tetranitrate , also known as PENT, PENTA, TEN, corpent, penthrite , is the nitrate ester of pentaerythritol. Penta refers to the five carbon atoms of the neopentane skeleton.PETN is most well known as an explosive...
).
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 electrical 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 filmPET film (biaxially oriented)
BoPET is a polyester film made from stretched polyethylene terephthalate and is used for its high tensile strength, chemical and dimensional stability, transparency, reflectivity, gas and aroma barrier properties and electrical insulation.A variety of companies manufacture boPET and other...
or kapton
Kapton
Kapton is a polyimide film developed by DuPont which can remain stable in a wide range of temperatures, from -273 to +400 °C...
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 (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
Another type of initiator that is rarely seen requires the use of a laserLaser
A laser is a device that emits light through a process of optical amplification based on the stimulated emission of photons. The term "laser" originated as an acronym for Light Amplification by Stimulated Emission of Radiation...
to initiate a carbon-doped explosive via a fiber optic. These initiators are highly reliable, and offer a number of advantages, primarily in that unintentional initiation is made very difficult. Without the correct laser initiation system, or a completely independent initiation system, these components are not capable of being controlled remotely.
History
The first blasting cap or detonator was demonstrated in 1745, when a Dr. Watson of the Royal SocietyRoyal Society
The Royal Society of London for Improving Natural Knowledge, known simply as the Royal Society, is a learned society for science, and is possibly the oldest such society in existence. Founded in November 1660, it was granted a Royal Charter by King Charles II as the "Royal Society of London"...
showed that the electric spark
Electric spark
An electric spark is a type of electrostatic discharge that occurs when an electric field creates an ionized electrically conductive channel in air producing a brief emission of light and sound. A spark is formed when the electric field strength exceeds the dielectric field strength of air...
of a Leyden jar
Leyden jar
A Leyden jar, or Leiden jar, is a device that "stores" static electricity between two electrodes on the inside and outside of a jar. It was invented independently by German cleric Ewald Georg von Kleist on 11 October 1745 and by Dutch scientist Pieter van Musschenbroek of Leiden in 1745–1746. The...
could ignite black powder.
In 1750, Benjamin Franklin
Benjamin Franklin
Dr. Benjamin Franklin was one of the Founding Fathers of the United States. A noted polymath, Franklin was a leading author, printer, political theorist, politician, postmaster, scientist, musician, inventor, satirist, civic activist, statesman, and diplomat...
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.
In 1822 the first hot wire detonator was produced by Dr Robert Hare. Using one strand separated out of a multistrand wire as the hot bridgewire, this blasting cap ignited a pyrotechnic mixture (believed to be potassium chlorate/arsenic/sulphur) and then a charge of tamped black powder.
In 1864 (dynamite not invented yet), Alfred Nobel
Alfred Nobel
Alfred Bernhard Nobel was a Swedish chemist, engineer, innovator, and armaments manufacturer. He is the inventor of dynamite. Nobel also owned Bofors, which he had redirected from its previous role as primarily an iron and steel producer to a major manufacturer of cannon and other armaments...
introduced the first Pyrotechnic Fuse blasting cap, using mercury fulminate to detonate dynamite
Dynamite
Dynamite is an explosive material based on nitroglycerin, initially using diatomaceous earth , or another absorbent substance such as powdered shells, clay, sawdust, or wood pulp. Dynamites using organic materials such as sawdust are less stable and such use has been generally discontinued...
.
In 1868, H. Julius Smith introduced a cap that combined a spark gap ignitor and mercury fulminate, the first electric cap able to detonate dynamite.
In 1875, Perry "Pell" Gardiner and Smith independently developed and marketed caps which combined the hot wire detonator with mercury fulminate explosive. 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 Gardiner and Smith caps.
Electric match caps were developed in the early 1900s in Germany, and spread to the US in the 1950s when ICI International
Imperial Chemical Industries
Imperial Chemical Industries was a British chemical company, taken over by AkzoNobel, a Dutch conglomerate, one of the largest chemical producers in the world. In its heyday, ICI was the largest manufacturing company in the British Empire, and commonly regarded as a "bellwether of the British...
purchased Atlas Powder Co. These match caps have become the predominant world standard cap type.
External links
- Blaster Exchange Explosives Industry Portal
- 1956 safety film "Blasting Cap - Danger!" from Prelinger ArchivesPrelinger ArchivesThe Prelinger Archives is a collection of films relating to U.S. cultural history, the evolution of the American landscape, everyday life and social history...