Innovative Initiation System- Digital Detonator

Innovative Initiation System- Digital Detonator Dr. A. K. Mishra Faculty, Department of Mining Engineering, Indian School of Mines, Dhanbad- 826 004

Keywords: Blasting; Initiation System; Electronic Detonator; fly Rock; Noise; Controlled Blasting.

ABSTRACT: Ever growing demand of mineral is forcing mine management to seek out and adopt technologies in order to produce mineral economically and efficiently. Today, many mine operators use the latest explosives, equipment, designs, and evaluation tools in an effort to ensure every kilogram of explosives being utilized to its fullest potential. Globally mine operators are using few hundred tonnes of bulk explosives in each round with variation of hole depths 35 m to 50 m and hole diameter from 259 – 310 mm. An accurate controlled sequence of blast detonation is a fundamental design parameter having a major direct impact on overall blast performance. Since it is also necessary to maintain ground vibration levels within permitted limits, the mining engineer usually prefers to have an initiating system, which should help in reduction of vibration levels along with the capability of improving rock fragmentation, particularly keeping the environmental aspects in the mind. As most of the Indian surface coal mines are reaching close to habitat, importance of time accuracy of initiators are becoming more important for the mine operators as little scatter of the order of 5%~10% can cause severe ground vibration and fragmentation problems. The need of time accuracy resulted in introduction of electronic detonators in the field of blasting applications. This paper discusses the features and benefits of comparatively new electronic detonator system in the mining field.

1 INTRODCTION Increased demand of mineral has compelled mineral industry to adopt mega projects with large size of blasts and higher capacity equipments. Hence, usage of large amount of explosives in the mines near town area has become a regular feature and it has increased public environmental consciousness. This has called for much greater control over blast induced ground vibrations, noise and fly rock. In search of better technology and enhancement of productivity every mine operator is trying to adopt the latest technology available globally. Every research and development effort has been put by the explosive and initiation system manufacturers to provide the best to the excavation industry and to a large extent they have succeeded as well. One specific technology in initiating systems that has been under development for several years, by several manufacturers, and is beginning to be tested and used increasingly in the industry is the electronic

detonator. It has been observed by many researchers that proper initiating system and precision of delay time in detonators offer great advantages in controlling ground vibrations, fly rock, noise and improving fragmentation. The technology of electronic detonators is becoming more and more advanced and being used popularly in production blasts. This is the fitting time for blasting engineers to fully explore the potential offered by electronic detonators. While electronic detonators are perfectly suited for controlled blasting in open pit mines, they also offer great flexibility to underground production blasts. In the underground blasting, creation of sufficient void or free face is influenced by having proper delay time. In underground blasts, delay time may not be properly used if there is not enough void/free face. In case of underground mining applications, detonators are required to have long delays and high precision for obtaining considerable amount of void/free face. Here, electronic detonators offer clear advantages over pyrotechnic detonators as the accuracy is about 1 ms and delay timings up to about 6 s can be achieved, [1].

2 IMPORTANCE OF INITIATION SYSTEMS IN BLASTING Blasting is usually the first step in any mining process and its results influence the efficiency of down stream processes to varying degrees. Blast results are considered good when they ensure good digging and loading operations while maintaining the safety and environmental standards. Initiator is a term that is used in the explosive industry to describe any device that may be used to start a detonation in explosive. Detonation is the process of propagation of a shock wave through an explosive, which is accompanied by a chemical reaction that furnishes energy to maintain the shock wave propagation in a stable manner. The devices that initiate high explosives are called detonators and devices that start burning or deflagration are called squibs or igniters. It is assumed that the holes have been laid out and drilled in the designed pattern and the objective of initiators is to communicate with the holes so that it may ensure: • The sequence in which the holes (or portions of the hole) should fire, • The time delay between holes, rows or decks, and , • The energy required to begin the detonation process, It has been emphasized that precisely controlled release of explosive energy in a sequence of blast holes yield better fragmentation. Hence, an accurate control is necessary over the blast detonation sequence to bring direct impact on over all blast performance. Any variation in hole detonation timing results in that hole being fired prior to or after its nominal firing time due to which holes could potentially detonate totally out of sequence causing improper relationships that can have adverse impacts on the performance of a blast. The results of these impacts have been briefed as following: • Poor rock fragmentation • Large amounts of oversize • High ground vibration levels • High air blast levels • Fly rock incidents • High downstream process costs The optimum delay pattern lies within the range of burden response time that allow good fragmentation and displacement of each burden without the presence of cutoffs. The delay interval required for optimum fragmentation varies with the type of rock, burden distances and type of explosive being fired. The best fragmentation is achieved when each charge is given sufficient time to break its quota of burden from the rock mass before the next charge

detonates. Hence, the initiation systems today required to set off many charges in many separate blast holes in a predetermined time delay pattern which is designed to provide optimal fragmentation and a minimum of ground vibration and fly rock. Currently, either detonating cord with cord relays or shock tube initiation system with trunk line delays or electric delay detonators are used to provide proper delay between holes or rows for proper control over fragmentation, ground vibration, noise, back break and fly rocks. All these systems are pyrotechnic based which provides scattering in firing from the designated time delay. This has called for development of a system with precision in time delay and with the efforts of scientists in the beginning of 20th century electronic detonators evolved. 3 ELECTRONIC DETONATORS At the beginning of the 20th century, a combination of primary and secondary explosives began to be used in detonators. During the last part of this century, significant progress in detonator technology has made it possible to transfer the ignition energy to the detonator in a variety of ways via electric wires and fuse heads, or via the NONEL tube. Pyrotechnic delay elements with a wide span of high-precision burning rates have been developed in 1950s with the introduction of short-delay or millisecond-delay blasting with 25 ms intervals which was a major break thorough for controlling the rock blasting process that made possible to minimize ground vibrations and fly rock while simultaneously improving the fragmentation. Drifting and tunnelling demands half-second interval times and today the use of high precision delays up to 6 second is in practice. The scatter with pyrotechnic delay charges can be held to within 1.5 to 2.5% of the nominal delay time for short delays. The scatter in firing times has decreased with the successive introduction of more and more refined detonator systems in the past (Figure 1). Over the years the manufacturers of pyrotechnic delays have invested in manufacturing, process, and chemical improvements in order to achieve the high level of precision and accuracy. Even though the improvements have been made significantly, the most precise pyrotechnic delay compositions in a detonator are influenced by the following problems causing scattering in time, [2]: • The detonator delay compositions can shift over time due to the chemistry of fuel and oxidizers in the mix • The variation in the burning rate of delay element

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The temperature and moisture condition at time of use or storage may affect delay performance • The humidity and storage conditions may affect performance Cap scattering of pyrotechnic based detonators called for launching of electronic detonator technology to replace the conventional pyrotechnic delay elements for having better blasting results in terms of fragmentation with vibration control. The electronic detonator has basically integrated circuits that produce precise timing in microseconds rather than in milliseconds, as it is the case with pyrotechnic delays, PERSSON ET AL, [3]. The electronic detonators have been manufactured by the various manufacturers in different trade names as given below: • Daveytronic® digital blasting system • Deltadet II ™ system (Delta cap initiators) • SDI Electronic ignition module • Hotshot • i-kon™ digital energy control system (Orica Explosives) • UNI Tronic ™ Electronic Blasting System [Sasol Mining Initiators Africa (Pty) Ltd., SA] • SMARTDET ®, ELECTRODET® (African Explosives Ltd.) • Digidet® (Dyno Nobel)

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Safety fuse Ordinary / Electric detonators Second-interval detonators Short delay detonators High precision caps Electronic detonators

3.1 Electronic detonator – design aspects The electronic detonator system has three closely interacting main components, namely, the detonator, logger and the blasting machine, which are necessary for the proper functioning of the system. Detonator All the electronic detonators utilize stored electrical energy inside the detonator as a means of providing the time delay and initiation energy. But the other initiating systems utilize pyrotechnic energy as a means of delay and initiation. Although construction may not appear to be significantly different, there is a very basic design difference between an electronic detonator and the other two (shock tube and electric). The igniter in the electronic design is positioned below the delay (timing) module, whereas both the shock tube detonator and the electric detonator utilize the igniter ahead of the delay module (shock tube functions as the igniter in the shock tube device), which can be seen in figure 2. The electronic detonator design also differs from the other two with the use of some type of stored (electrical) energy device, typically a capacitor, in the delay module(s).

pical s A typical section of an electronic detonator is shown in the figure 3. In principle, the detonator consists of an electronic delay unit in combination with an instantaneous detonator. An integrated circuit on a microchip constitutes the heart of the detonator. The microchip circuitry includes an oscillator for timing, memory for retaining its programmed delay, and communication functions to receive and deliver digital messages to and from the control equipment. The detonator has a capacitor, which can store sufficient energy to run the microchip independent of external power for 8 seconds and also to separate circuits on the input side (toward the lead-in wires) in order to protect against various forms of electric overload. The chip itself also has internal safety circuits in the

inputs. The fuse head for initiating the primary charge is specially developed to provide a short initiation time with a minimum of time scatter.

to reduce the risk of any unintentional initiation coming from other energy sources. Mode of operation The preparatory work for a blasting operation includes determining the delay time for each blast hole in the round and charging the holes with detonators of suitably chosen period numbers. The blasting machine’s time memory is then programmed with the necessary time information adapted to the period numbers chosen. This can be carried out by logger, which is connected to the blasting machine.

The detonator has the similar dimensions of a conventional electric detonator with two wires, which are usually marked with delay numbers between 1 and 250. These period numbers do not indicate the delay time but only the order in which the detonators will go off. Each detonator has its own time reference, but the final delay time is determined through interaction between the detonator and the blasting machine only immediately before initiation. Logger The logger is used to communicate with the detonators during the hookup. It operates usually at an inherently safe voltage, the logger recognizes and checks each detonator as it is clipped onto the harness wire. The required delay time for each detonator is entered and written into logger memory. This information is stored in non-volatile memory (hard memory) of the logger and used to program each detonator only during the firing sequence. At any stage the logger can be used to check the hook-up and get the response from every detonator, KAY, [4].

Connection An outline of a round using this system is shown in figure 4. The detonators in the round are connected in parallel rather than in series with arbitrary polarity. The parallel connection is made if a faulty detonator is registered, the blast can still proceed, as the circuit will not be affected by the fault, WORSEY and LAWSON, [5]. The parallel connection is done by connecting each detonator to a two-wire bus cable via a terminal block, using pliers. It is not necessary to strip the lead wires or the bus cable before connecting. If an error occurs, this is automatically detected by the pliers. Finally, the bus cable is connected to the blasting machine via terminal box and a firing cable.

Blasting machine The blasting machine constitutes the central unit of the initiation system. This machine communicates to each detonator in turn via the logger. The unit is basically microcomputer controlled and its mode of operation can be altered with various control programs that gives part of the flexibility of the system. A panel with lamp indicates the current status and gives proceed signal when the round is ready to be fired. If any errors occur, they are immediately indicated on the panel and the machine resets the system. The ready signal for firing is given only after receiving the satisfied operation status from the system. The delay timing allocation is made by the unique coded signals exclusively coming form the blasting machine to eliminate the possibility of error and also

Electronic detonator systems can first be grouped into two basic categories: • Factory Programmed Systems • Field Programmed Systems Factory Programmed Systems, in most cases, have a fairly close resemblance to the conventional hardware and components found with standard electric detonators. In some cases, the user may even have a difficult time differentiating a wired electronic detonator from a wired electric detonator. Even though these units may not appear to be different, electronic detonators generally cannot be fired or shot using conventional blasting machines or firing devices. Each system will have a unique firing

code or communication protocol, used to fire the detonators in the blast. Factory Programmed Systems can be further grouped into specific types or styles. There are electrically wired systems, where each manufacturer has a specific wiring style or methodology, and a factory programmed system that utilizes shock tube technology to energize an electronic timing circuit within the detonator. Factory programmed systems utilize "fixed" delay holes which are generally loaded and hooked up in the same manner as standard electric or shock tube systems. Depending on the manufacturer, some type of surface connector may be utilized for ease of wiring, or maintenance of correct electrical polarity. Field Programmed Systems utilize electronic technology to program delay times "on the bench". Each system is manufactured with unique system architectures, styles, hardware and communication protocol. There are no fixed delay times associated with these detonators. These systems rely on direct communication with the detonator (either prior to loading, after loading, or just prior to firing) for the proper delay time and subsequent blast design. In general, these systems will utilize some type of electronic memory, which allows them to be reprogrammed at any time up until the fire command is given. 3.2

Characteristics of Electronic Detonators

The characteristics or important features of an electronic detonator include: • • • • • • • •

The detonator initially has no initiation energy of its own. The detonators can be programmable from 1 to 8000 milliseconds in one-millisecond increments. The detonator cannot be made to detonate without a unique activation code. The detonator receives its initiation energy and activation code from the blasting machine. The detonator is equipped with over-voltage protection. The short delay time between two adjacent period numbers (equal to the shortest interval time) is 1 ms. The long delay time is 6.25 seconds. A detonator with a lower period numbers cannot be closer to each other in delay time than the difference in their numbers. (For ex-

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ample, the interval time between No.10 and No.20 must be at least 10 ms) The maximum number of detonators connected to each blasting machine is about 1600, KAY, [4]. In comparison to shock tube initiation systems, the electronic detonators scatter percentage varies around 0.01 percent for any programmed delay period, where as the shock tube initiation systems has the scatter percentage variation of 3.5 to 5.5 percent, GROBLER, [6]. The system has full two-way communication between detonators and control equipments.

3.3 Benefits of Electronic Detonators It has been found that electronic detonators offer the following advantages: • Inherent safety - with built in protection from static electricity, stray currents, radio frequency and high voltage. • Electronic detonators can be programmed to fire at any time from 0 ms to 8000 ms in steps of 1 ms, which makes it possible to select the best delay time between holes and rows to suit the particular characteristics of each blast, rather than having to choose from set numbers such as 17 ms or 25 ms. • A factory-programmed security code unique to the operator that will provide more security and prevent unauthorized use. • Interactive facilities with full two way communication ability – as well as being programmed and armed by the system for checking the status of the detonator and making a circuit check before firing. • The reduced delay and accuracy of the electronic detonators result in improving the fragmentation in surface mining with a reduction in the upper size classes (oversized material) and the fines, which in turn slash down the power consumption significantly in the primary and secondary crushers as well as total throughput, BOSMAN ET AL, [7]. • Electronic detonators improve face advance and provide safe working environment as it reduces the over break in tunnelling. • The possibility of having a presplit effect in the blasts if delay timing between holes using the shock tube initiation system below 11 ms can be over come with the availability of short delay electronic detonators GROBLER, [6].

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Reduced stock management – as electronic detonators are programmable, only one type of detonator is required to be stored in the magazine. The absolute accuracy of electronic detonators ensures each blast hole fires exactly when it is supposed to fire. All mines, which have used electronic detonator, have witnessed 10% or more relative improvement in casting. By selection of proper delay timings, blast vibration energy can be channeled such that predominant energy falls into higher frequency range and so it offers a tool for vibration control and frequency channeling BHUSHAN [8]. The flexibility of selecting the timing of holes offers blast designer to create separate muckpile of different grades to get ore and waste separation by re-establishing relief at any stage of progression of blast.

3.4 Reasons for poor popularity of electronic detonators among the users It has been observed that the following factors are contributing towards the less popularity of electronic detonator among the users in the global, BRACE [9]. • Lack of understanding of the negative implications of pyrotechnic scatter. • Perception that they are over-priced. • Budget-controlled management systems. • Disbelief in reported successes. • Perceptions that the benefits of electronic systems are limited to some applications only. • Archaic regulations having the effect of entrenching outdated technologies. • Poor reliability, robustness, set against a very high price premium. • Poor marketing, spelling out of benefits, delivery, support, etc. • Difficulties and cost in gaining approvals. • Bad estimates of market potential. • Unexpected competitive reactions. • Poor timing of introduction and rapid market changes after introduction. • Inadequate quality control of a bad product. • Wrong estimates of production costs. • Poor market testing (price and performance) and improper channels of distribution.

3.5 Applications of digital detonators in India The electronic initiation system has been launched in India by Indian Explosives Limited, a wholly owned subsidiary of Orica, Australia. It has been used at Zawar mines of HZL, Jayant and Dudhichua mines of NCL and West Bokaro Colliery of TISCO. The digital detonators have globally found their applications in the following areas: • Improving contour blasting and decreasing the need for the rock support, • Minimising ground vibrations, • Reducing damage to mine infrastructure and nuisance to society, • It is used regularly for production blasting in strip mining of coal and casting of overburden, open pit mining of copper, massive mining of diamond and zinc, stone quarries, narrow reef mining of gold and platinum, and in development of under ground excavations, • Optimizing the rock fragmentation in underground and surface mine blasts, • The electronic detonators are preferred where large sized blasts can be fired at risky locations, and have their delay sequencing optimized to maximize fragmentation and minimize other environmental hazards. 3.6 Precautions while using Electronic Detonators The blasting personnel should adopt the following precautions while handling the electronic detonators in the field. • It is always necessary to follow manufacturer’s warning and instructions, especially hook-up procedures and safety precautions. • The electronic detonators must be fired with the equipment and procedures recommended by the manufacturer. • The integrity of the detonator system must be verified prior to initiation of a blast. • The firing circuit should be completely kept insulated from ground or other conductors. • The wires, connectors and coupling devices as specified by the manufacturer should be used. • A minimum of 30 minutes should be sufficiently given before returning to a blast site after aborting a blast unless the manufacturer provides other specific instructions. • The blast area should be cleared of personnel, vehicles and equipment prior to hooking up to the firing device or blast controller.

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The detonator leads, coupling devices and connectors should be fully protected until ready to test or fire the blast. The wire ends, connectors and fittings must be kept clean and free from dirt or contamination prior to connection. It is always necessary to follow manufacturer’s instructions for system hook-up of electronic detonators. The manufacturer’s recommended practices to protect electronic detonators from electromagnetic, radio frequency, or other electrical interference sources should be strictly followed in the field. The electronic detonator wires, connectors, coupling devices, shock tube or other components should be protected from mechanical abuse and damage. The blaster should ensure that he has control over the blast site throughout the programming, system charging, firing and detonation of the blast The extreme care should be maintained when programming delay times in the field to ensure correct blast designs as an incorrect programming can result in misfires, fly rock, excessive air blast and vibration. The electronic detonators and electric detonators should not be kept in the same blast, even if the same manufacturer makes them, unless the manufacturer approves such use. The electronic detonators of different types and/or versions in the same blast, even if the same manufacturer makes them, unless the manufacturer approves such use. The test equipment and blasting machines designed for electric detonators should not be used with electronic detonators. The equipment or electronic detonators that appear to be damaged or poorly maintained should be prohibited from use in the field. The blasting machines, testers, or instruments with electronic detonators that are not specifically designed for the system should not be used. The attempt to cut and splice leads should not be made unless specifically recommended by the manufacturer. The final hook-up to firing device or blast controller should not be made until all personnel are clear of the blast area and they must be withdrawn to a safe location. The blast holes in open work near electric power lines should not be charged unless the

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firing lines and detonator wires are secured or are too short to reach the electric power lines. The handling or use of electronic detonators during the approach and progress of an electrical storm must be strictly prohibited. The electronic detonator systems outside the manufacturer’s specified operational temperature and pressure ranges should never be used. Under no circumstances, the testing or programming of an electronic detonator in a booster, cartridge or other explosive component (Primer Assembly) should be done unless it has been charged in the blast hole. The electronic detonator should not be kept in hand while it is being tested or programmed.

4 CONCLUSION Blasting is an integral part of mining, tunneling and construction industry. Apart from the performance, the blasting should also satisfy the requirements of environmental thresholds set by regulatory organizations in terms of reduction in ground vibration, air blast etc. With the efforts of many researchers and scientists at last a flexible and accurate initiation system is available with blasting engineer. It has been observed that the electronic delay detonators improve the blasting performance for both open pit and under ground operations. The accuracy, precision, flexibility and methodology of electronic detonators offer enhanced safety and improved productivity. The improved productivity is in the form of fragmentation control, extraction of blast geometries and preservation of the integrity of the in-situ rock mass. It has also found acceptance in underground tunneling, with outstanding improvements in both advance and back break, and has been delivering unique ore recovery and productivity benefits in massive mining. Continuous improvement is a necessary part of blasting to maximize crusher throughput, minimize waste and lower the total cost of production. Here, the flexible programming capability of electronic detonator system allows for the development of new initiation sequences to provide new solutions to the mining and construction industry.

5 REFERENCES [1] RUSTON, P.A., (2002): Blasting Technology Research and Development in the 21st Century, Proceedings of Seventh International Symposium on Rock Fragmentation by Blasting, Beijing, China, 11~15, August,2002:10-16, Metallurgical Industry Press. [2] WATSON, J.T., (1997): A New Generation of Shock Tube Detonators, Proceedings of Seventh High-Tech Seminar on State-of-the-Art of Blasting Technology, Instrumentation and Explosives Applications, Orlando, USA, 28 July – 1 August, Blasting Analysis International Inc. Press. [3]

PERSSON, P.A., HOLMBERG, R., & LEE, J., (1994): Rock Blasting and Explosive Engineering, 540, CRC Press, USA – ISBN 08493-8978-X.

[4]

KAY, D., (2000): Digital Blasting –An Opportunity to Revolutionise Mass Underground Mining, Proceedings of Seminar on MassMin, Brisbane, Queensland, Australia, 29 October ~ 2 November 2000: 155-161.

[5] WORSEY, P.N., and LAWSON, J.T., (1983): The Development Concept of the Integrated Electronic Detonator, Proceedings of the First International Symposium on Rock Fragmentation by Blasting, Lulea, Sweden : 251-258. [6] GROBLER, H.P., (2003): Using Electronic Detonators to Improve All-Round Blasting Performance - Fragblast, 7, 1:1-12. [7] BOSMAN, H.G., BEDSER, G., and CUNNINGHAM, C.V.B., (1997): Production Blasting with Electronic Delay Detonators at Peak Quarry, Institute of Quarrying of South Africa, South Africa. [8] BHUSHAN, V., (2004): Electronic detonatorsnew era in blasting technology, Journal of Mines Metals and Fuels, Vol. 52, No. 11, pp 298-302. [9] BRACE, S., (2004): Electronic Detonator and Initiation Systems - Implications of the Dominant Design for Widespread Acceptance and Sales of this ‘New’ Technology, Proceedings of the Thirtieth Annual Conference on Explosives and Blasting Technique, New Orleans, Louisiana, USA, 1-4, February,

2004:International Society Of Explosives Engineers, Ohio, USA.