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, equip-ment, designs, and evaluation tools in an effort to ensure every kilogram of explosives being utilized to itsfullest potential. Globally mine operators are using few hundred tonnes of bulk explosives in each round withvariation of hole depths 35 m to 50 m and hole diameter from 259 – 310 mm. An accurate controlled se-quence of blast detonation is a fundamental design parameter having a major direct impact on overall blastperformance. 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 themind. As most of the Indian surface coal mines are reaching close to habitat, importance of time accuracy ofinitiators are becoming more important for the mine operators as little scatter of the order of 5%~10% cancause severe ground vibration and fragmentation problems. The need of time accuracy resulted in introduc-tion of electronic detonators in the field of blasting applications. This paper discusses the features and bene-fits 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 in-creased public environmental consciousness. This has called for much greater control over blast in-duced ground vibrations, noise and fly rock. In search of better technology and enhancement of pro-ductivity every mine operator is trying to adopt the latest technology available globally. Every research and development effort has been put by the explo-sive and initiation system manufacturers to provide the best to the excavation industry and to a large ex-tent they have succeeded as well. One specific tech-nology in initiating systems that has been under de-velopment 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 control-ling 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 blast-ing 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 under-ground production blasts. In the underground blast-ing, creation of sufficient void or free face is influ-enced 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 consid-erable 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 proc-ess 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 de-vice that may be used to start a detonation in explo-sive. Detonation is the process of propagation of a shock wave through an explosive, which is accom-panied 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 as-sumed 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 en-sure:

• 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 re-lease of explosive energy in a sequence of blast holes yield better fragmentation. Hence, an accurate control is necessary over the blast detonation se-quence to bring direct impact on over all blast per-formance. 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 poten-tially detonate totally out of sequence causing im-proper 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 pres-ence of cutoffs. The delay interval required for op-timum 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 re-quired 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 develop-ment 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 cen-tury, 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 vi-brations and fly rock while simultaneously improv-ing the fragmentation. Drifting and tunnelling de-mands 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 de-creased 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 sig-nificantly, the most precise pyrotechnic delay com-positions in a detonator are influenced by the follow-ing 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

• The temperature and moisture condition at time of use or storage may affect delay formance

per- The electronic detonator system has three closely interacting main components, namely, the detonator, logger and the blasting machine, which are neces-sary for the proper functioning of the system.

• The humidity and storage conditions may af-fect performance

Cap scattering of pyrotechnic based detonators called for launching of electronic detonator technol-ogy to replace the conventional pyrotechnic delay elements for having better blasting results in terms of fragmentation with vibration control. The elec-tronic detonator has basically integrated circuits that produce precise timing in microseconds rather than in milliseconds, as it is the case with pyrotechnic de-lays, PERSSON ET AL, [3]. The electronic detonators have been manufactured by the various manufactur-ers 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)

a. Safety fuse b. Ordinary / Electric detonators c. Second-interval detonators d. Short delay detonators e. High precision caps f. Electronic detonators

3.1 Electronic detonator – design aspects

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 elec-tric). The igniter in the electronic design is posi-tioned below the delay (timing) module, whereas both the shock tube detonator and the electric deto-nator 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 elec-tronic 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 in-stantaneous detonator. An integrated circuit on a mi-crochip 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 digi-tal 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 ini-tiation time with a minimum of time scatter.

The detonator has the similar dimensions of a con-ventional 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 refer-ence, 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 detona-tors during the hookup. It operates usually at an in-herently safe voltage, the logger recognizes and checks each detonator as it is clipped onto the har-ness wire. The required delay time for each detona-tor 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].

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 ba-sically microcomputer controlled and its mode of operation can be altered with various control pro-grams 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 indi-cated on the panel and the machine resets the sys-tem. The ready signal for firing is given only after receiving the satisfied operation status from the sys-tem. 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

to reduce the risk of any unintentional initiation coming from other energy sources.

Mode of operation

The preparatory work for a blasting operation in-cludes determining the delay time for each blast hole in the round and charging the holes with detonators of suitably chosen period numbers. The blasting ma-chine’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.

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 polar-ity. The parallel connection is made if a faulty deto-nator 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 con-necting. If an error occurs, this is automatically de-tected by the pliers. Finally, the bus cable is con-nected to the blasting machine via terminal box and a firing cable.

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 elec-tric detonators. In some cases, the user may even have a difficult time differentiating a wired elec-tronic detonator from a wired electric detonator. Even though these units may not appear to be differ-ent, electronic detonators generally cannot be fired or shot using conventional blasting machines or fir-ing 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 elec-trically wired systems, where each manufacturer has a specific wiring style or methodology, and a factory programmed system that utilizes shock tube tech-nology 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 stan-dard 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 tech-nology to program delay times "on the bench". Each system is manufactured with unique system architec-tures, 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 elec-tronic memory, which allows them to be repro-grammed at any time up until the fire command is

iven. g 3.2 Characteristics of Electronic Detonators

The characteristics or important features of an electronic detonator include:

• The detonator initially has no initiation en-ergy of its own.

• The detonators can be programmable from 1 to 8000 milliseconds in one-millisecond in-crements.

• The detonator cannot be made to detonate without a unique activation code.

• The detonator receives its initiation energy and activation code from the blasting ma-chine.

• 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-

ample, the interval time between No.10 and No.20 must be at least 10 ms)

• The maximum number of detonators con-nected to each blasting machine is about 1600, KAY, [4].

• In comparison to shock tube initiation sys-tems, the electronic detonators scatter per-centage 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 fre-quency 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 se-lect 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 secu-rity and prevent unauthorized use.

• Interactive facilities with full two way com-munication ability – as well as being pro-grammed and armed by the system for checking the status of the detonator and mak-ing a circuit check before firing.

• The reduced delay and accuracy of the elec-tronic detonators result in improving the fragmentation in surface mining with a re-duction 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].

• 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 detona-tors ensures each blast hole fires exactly when it is supposed to fire. All mines, which have used electronic detonator, have wit-nessed 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 fre-quency range and so it offers a tool for vibra-tion 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 impli-cations 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 en-trenching outdated technologies.

• Poor reliability, robustness, set against a very high price premium.

• Poor marketing, spelling out of benefits, de-livery, 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 ap-plications 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 overbur-den, open pit mining of copper, massive min-ing of diamond and zinc, stone quarries, nar-row reef mining of gold and platinum, and in development of under ground excavations,

• Optimizing the rock fragmentation in under-ground and surface mine blasts,

• The electronic detonators are preferred where large sized blasts can be fired at risky loca-tions, and have their delay sequencing opti-mized to maximize fragmentation and mini-mize 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 manufac-turer’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 suffi-ciently 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 person-nel, vehicles and equipment prior to hooking up to the firing device or blast controller.

• 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 contami-nation prior to connection.

• It is always necessary to follow manufac-turer’s instructions for system hook-up of electronic detonators.

• The manufacturer’s recommended practices to protect electronic detonators from elec-tromagnetic, radio frequency, or other elec-trical interference sources should be strictly followed in the field.

• The electronic detonator wires, connectors, coupling devices, shock tube or other com-ponents should be protected from mechanical abuse and damage.

• The blaster should ensure that he has control over the blast site throughout the program-ming, system charging, firing and detonation of the blast

• The extreme care should be maintained when programming delay times in the field to en-sure correct blast designs as an incorrect pro-gramming can result in misfires, fly rock, ex-cessive air blast and vibration.

• The electronic detonators and electric deto-nators 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 instru-ments 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 recom-mended by the manufacturer.

• The final hook-up to firing device or blast controller should not be made until all per-sonnel 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

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 elec-trical storm must be strictly prohibited.

• The electronic detonator systems outside the manufacturer’s specified operational tem-perature and pressure ranges should never be used.

• Under no circumstances, the testing or pro-gramming of an electronic detonator in a booster, cartridge or other explosive compo-nent (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 pro-grammed.

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 organiza-tions 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, preci-sion, flexibility and methodology of electronic deto-nators offer enhanced safety and improved produc-tivity. 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 nec-essary part of blasting to maximize crusher through-put, minimize waste and lower the total cost of pro-duction. Here, the flexible programming capability of electronic detonator system allows for the devel-opment of new initiation sequences to provide new solutions to the mining and construction industry.

5 REFERENCES

[1] RUSTON, P.A., (2002): Blasting Technology Re-

search and Development in the 21st Century, Proceedings of Seventh International Sympo-sium on Rock Fragmentation by Blasting, Bei-jing, China, 11~15, August,2002:10-16, Metal-lurgical Industry Press.

[2] WATSON, J.T., (1997): A New Generation of

Shock Tube Detonators, Proceedings of Sev-enth High-Tech Seminar on State-of-the-Art of Blasting Technology, Instrumentation and Ex-plosives 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 Engi-neering, 540, CRC Press, USA – ISBN 0-8493-8978-X.

[4] KAY, D., (2000): Digital Blasting –An Oppor-

tunity 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 Elec-tronic Detonator, Proceedings of the First In-ternational Symposium on Rock Fragmentation by Blasting, Lulea, Sweden : 251-258.

[6] GROBLER, H.P., (2003): Using Electronic Deto-

nators to Improve All-Round Blasting Per-formance - Fragblast, 7, 1:1-12.

[7] BOSMAN, H.G., BEDSER, G., and CUNNING-

HAM, 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 detonators-new 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 Domi-nant Design for Widespread Acceptance and Sales of this ‘New’ Technology, Proceedings of the Thirtieth Annual Conference on Explo-sives and Blasting Technique, New Orleans, Louisiana, USA, 1-4, February,

2004:International Society Of Explosives En-gineers, Ohio, USA.