As explained in a previous article, “Burning fuses has been first in use to delay the ignition and for the blaster to stay at a safe distance from the explosion. The burning time introduces a flexible delay which depends on the length of the burning fuse. (…) The flame serves as a detonator and the delay is the length of the fuse. Even the most advanced initiation technologies keep on using the same concepts, though sometimes along different forms.”
Blasting caps come in a variety of forms. Fuse caps, electric detonators, non-electric detonators and electronic detonators are the different types of detonators you can find on the market.
The invention of the successive generations of fuse caps aims to answer the hazardous ignition of the explosives product used during the considered period. Miners’ safety has always been one of the main objectives in blasting accessories development.
Black powder is said to be a Chinese invention, used as fireworks, dated from the first centuries of our era. Despite the use of black powder-based “Greek-fires” in ancient battles, 1380 is a commonly acknowledged date for the first studies on black powder. German Franciscan Monk, Berthold Schwarts developed gunpowder from the antique formula. The first recorded use of black powder for rock blasting dates back to 1627, in Hungary.
Its unreliable burning speed nevertheless makes the black powder extremely dangerous and results in many accidents.
This hazardous ignition was overcome in 1831 with the invention of the "Miners Safety Fuse" by William Bickford, a rope with a strand of yarn infused with black powder.
Ascanio Sobrero synthetized nitroglycerin in 1846. Nitroglycerin is the first discovered explosive to be stronger than black powder. Its use on the field remains especially dangerous especially until 1863, when Alfred Nobel unveiled its "practical detonator": a wooden plug of black powder inserted into larger charge of liquid nitroglycerin, enclosed in a metal shell. In 1865, Nobel developed a mercury blasting cap which represents a substantial reduction in production costs and therefore contributed to its spread throughout the industry.
Being very cheap, fuse caps are still widely used today in the mining industry, especially in developing countries. Fuse caps are also, by design, insensitive to electromagnetic fields.
The first prototypes of detonators using electricity as an initiation signal energy source emerged in the late 1880s.
Electric blasting caps are similar to fuse caps, but with two insulated electric wires protruding from one end, instead of the fuse.
Instantaneous electric detonators were developed first. In 1868, H. Julius Smith patented an easier and safer technology, allowing the ignition through a mercury fulminate mixture, a high-resistance platinum bridge wire and a sulfur plug.
The inclusion of a delay powder train allowed the introduction of pre-programmed electric delayed detonators. This technology allows an offset between two consecutive charges and therefore, the creation of initiation sequences, opening doors to more controlled shots but limited to a finite number of combinations. Half-second delay detonators appeared in the early 1900s, while millisecond delay detonators arrived in the market in 1943.
Electric detonators are sensitive to heat, shock, static electricity, radio frequency energy and electromagnetic radiation.
Total non-electric initiation systems, where the initiation source comes from a shock wave, were developed in 1960s by Dyno Nobel. Non-electric detonators hit the market in 1973, offering all the advantages of electric initiation but adding safety benefits (insensitivity to electricity, radio frequency energy and electromagnetic radiation) and a wide operational flexibility (easier to design larger initiation sequences, theoretically with an unlimited number of delays).
This initiation system is composed of shock tubes connected to down-the-hole detonators and surface connectors. Though their coating of reactive powders and thanks to a starter, shock tubes transmit shock waves to the non-electric detonators. Connection on the field is “plumbing-like”, assuming the shock-wave is like water, circulating in the tube from a detonator to another.
Non-electric detonators are widely used, worldwide. The United States has always been one of the largest markets for this type of detonators.
Electronic components were introduced in the electric initiation’s world in the late 1960’s. Increasing the size of each shot turns to be strategic to the initiators market, for the electric detonators to be able to compete with the newly introduced non-electric detonators.
The electronic developments make the creation of a sequential blasting machine possible. The sequential blasting machine delivers electronically adjustable timed bursts of energy to a number of lead wires, dramatically increasing the maximum number of electric detonators the blasters can connect and therefore increase the number of potential combinations.
In the 1990’s, the increasing miniaturization of electronic components gave birth to a new idea: using an embarked electronic clock to replace the pyrotechnical (powder) delay element that creates inaccuracy for the electric detonators.
From 1990 to 2000, massive research and development movement was conducted by a large number of actors to develop pre-programmed or programmable electronic detonators. Programmable electronic detonators represent a step ahead in the logic, offering an amazing flexibility in the choice of initiation timing. This flexibility together with the electronically controlled accuracy opens doors for short delays complex initiation sequences that have since demonstrate significant benefits (nuisance reduction, productivity increase) to mining stakeholders. Numerical simulation software tools have been developed to help mining engineers to deal with such a huge number of possibilities in the design of their shots.
Despite a higher market price, electronic detonators steadily spread on the market during the 2000’s. A strong merger and acquisition stage has resulted in the disappearance of a large portion of the manufacturers. Nowadays, only 5 or 6 manufacturers remain active on this market.
Each brand can be programmed only by its own specifically designed blasting machine. Due mainly to different communication protocols, none of these machines can be used to initiate several brands of detonators. Consequently, none of these brands can be mixed in a single shot.
The first wireless blasting machine appeared on the market in 2000, allowing the initiation of bigger shots from a safer distance. Wireless initiation has become since a standard on the market.
Electronic detonators are still based on electrical wiring to conduct the initiation signal energy source. ORICA Mining Services, the inventor of a wireless electronic detonator unveiled in early 2011, pretends now to end with this operational weakness (potential leakage, shorts, cut-off, electromagnetic sensitivity) and consequently increases safety and mine profitability.
To be continued!