Programmable Electronic Detonator

Electronic Detonator System For Large Mines

Electronic Delay Detonator System For Large Mines *** Precise, Programmable and Accurate Delay Timing Results In Techno-Economic Benefits And Allows To Adopt “Signature-Hole Blast Analysis” Technique To Mitigate Blast Induced Ground Vibration *** Partha Das Sharma (B.Tech-Hons. In Mining Engg.) E.mail - [email protected], Website: http://miningandblasting.wordpress.com/ Abstract By more accurately controlling timing delays, electronic detonator system can increase rock fragmentation, lower vibration levels, reduce oversize; lessen the potential of fly-rock. This translates into faster excavation times and improves downstream processing costs for the mining operation by increasing throughput, reducing crusher wear, and lowering power consumption and maintenance costs. Apart, accurate delay timing programmable electronic detonators enable to adopt innovative ‘Signature-hole blast analysis’ technique to simulate, predict and control blast induced ground vibration, in order to obtain maximum operational efficiency, such as raising quantity of explosives per delay (kg/delay) etc. Research studies had indicated that blast vibration could be simulated by detonating a “Signature Hole” with the vibration monitored at critical locations, and then using a computer to superpose the waveforms with varying delays. By choosing delay times (∆t) that create ‘destructive interference’ at frequencies that are favored by the local geology, the “ringing” vibration that excites structural elements in structures, houses and annoys neighbors could be reduced. Computer analysis determines the application of delay timing between holes and between the rows. 1. Introduction - The mining and explosive industries rapidly embracing new technologies, in order to improve overall performance, efficiency and cost-effectiveness in various types of blasting and also to mitigate its adverse effects. Most recently, technology that is developed to improve techno-economics and reduction of most of adverse effects in usage of explosive and blasting is “Precise and Accurate Delay Timing – Digital or Electronic Detonator” system. Broadly speaking, accurate and flexible timing allows blasters to make small hole-to-hole and row-to-row changes to account for drilling inaccuracies. Adjusting the blast design to actual conditions can improve safety and fragmentation, which can cut costs by optimizing the loading and hauling cycle, increasing crusher throughput, and reducing the amount of oversize handling and secondary breaking. In addition, precise and variable delay timing manipulations have enhanced high-wall stability and bench crest preservation, resulting in safer mines operations and also for reduction of blast induced ground vibration. These improvements allow for more accurate placement of boreholes for succeeding blasts. Thus, the precision in delay timing has advantages such as: a) Better ground vibration control, b) Better fragmentation, c) Better control of rock movement and muck profile, d) Enhancement in productivity by optimizing utilization of explosive energy.

Author: Partha Das Sharma (E.mail: [email protected]) Website: http://miningandblasting.wordpress.com/

1


Mining activities remain a time and cost-intensive business therefore, accurate planning, cost efficiency have been the important factors in excavation operations. In a move to improve overall cost-efficiency in large mining and construction operations operators are adopting the use of Electronic Detonation blasting technology. The accuracy and flexibility of the programmable detonator have provided the mining industry with options, previously not available, to improve timing designs for increased benefit in the areas of ground control and better fragmentation. The industry’s whole approach to blast timing design can now be focused on greater safety, increased productivity and blast performance, rather than being restricted by the limited interval selections and inaccuracies the conventional pyrotechnics timing systems offer. Similarly, blasting is the primary crushing stage for stone producers in construction industry. The efficiency of downstream processing hinges on the success of the blasting program. The growing popularity of high-accuracy electronic detonators means the potential for an expansion of a quarry blasting program's capabilities and improved safety as well. 2. Understanding Electronic Delay Initiation system – In order to understand the Electronic delay initiation system, we discuss below few points regarding Pyrotechnic and Electronic delay system: (a) There are several types of electronic systems being tested and used in the mining industry, all of which utilize some type of stored energy device to provide energy for their timing and firing circuits. All Electronic Detonators has a system to store electrical energy inside the detonator as a means of providing delay timing and initiation energy.

Fig – 1


2


(b) All other existing conventional detonator technologies including shock tube, electric or safety fuse etc. utilizes pyrotechnic energy as a means of delay and initiation. Although construction of electronic detonator may not appear to be significantly different, there is a very basic design difference between an electronic detonator with other two shock tube and electric detonators. (c) One of the basic differences in electronic delay with pyrotechnic system of delay lies in the location of Igniter. In electronic detonator the Igniter is located below the delay (timing) module, whereas both shock tube and electric detonator (Fig – 1) utilizes the igniter ahead of delay element (shock tube function as igniter in the shock tube device). Other basic difference in design of electronic detonator is the use of some type of stored electrical energy device, typically capacitor, is used in the delay module. The construction and design of electronic detonator varies from manufacturer to manufacturer. (d) In case of electronic detonator which utilizes standard shock tube lead as the input signal, it transforms into electrical pulse through the use of a small explosive charge (booster) coupled to a highly efficient piezo ceramic element (generator) and (electrical energy storage cell (capacitor). Upon receipt of a thermal signal from shock tube the small explosive charge in the booster detonator fires. This activates the piezo ceramic device, which in turn causes current to flow through the steering diode to charge storage capacitor. A voltage regulator provides a substantially constant voltage source to oscillator to control the frequency (Example of this kind of system is DIGIDET TM of Ensign-Bickford, USA). (e) The Programmable electronic detonator (Fig – 2) utilizes standard lead as the input signal, which is transformed into electrical pulse through the use of principal component. Upon receipt of an electric signal causes current to flow through the steering diode to charge storage capacitor. A voltage regulator provides a substantially constant voltage source to oscillator to control the frequency. A “power on reset” circuit preloads the counter upon the initial application of the input voltage. Once the voltage on the storage capacitor has increased beyond a threshold setting the counter begin decrementing upon each input pulse from oscillator. As the counter digitally decrement past zero, the output to the firing switch activate and all remaining energy in the storage capacitor flows to the igniter. The end result is an electronic delay detonator. (f) Electronic Detonator system can be grouped into two basic categories – (i) Factory programmed system and (ii) Site programmed system or programmable system. i. ‘Factory programmed’ system generally has a close resemblance to the conventional system of standard pyrotechnic electric/shock tube detonators. Factory programmed system utilizes fixed delay period for the blast design. Holes are generally loaded and hooked up in the same manner as with standard electric and shock tube system. The major disadvantage of factory programmed fixed delay timing system lies in its non-flexibility in setting-up delay timings, results in generation of large inventory which becomes difficult to maintain. ii. ‘Site programmed or programmable’ system utilizes electronic technology to programmed delay timings “on the site”. There is no fixed delay times associated with these detonators. These systems rely on direct communication with the detonators for proper delay time as per design of blast, either prior to loading, after loading or just prior to firing. In fact, the system utilizes some type of electronic memory which allows them to be programmed at any time until the fire command is given. Due to its advantage of flexibility in assigning delay timings, the ‘site programmed electronic delay system’ is generally referred as ‘Electronic Detonator’.


3


Fig – 2 (g) Blast design software now-a-days have become foundation in drilling and blasting job in big mines in developed countries. Using the blast design software a blasting engineer can create the timing design in the office, simulate the blast on a PC, then optimize the design before providing the blast plan to field personnel. With electronic detonator system, very easily initiation system can be integrated with blast design software and the optimization of design becomes much easier. (h) A few companies abroad have come up with electronic detonator system with the capability of ‘Remote Programming and Remote Initiation’. The blasting sequence can be sent and the blast initiated by an encrypted radio frequency protocol. This eliminates the use of lead-in cable and increases the safety distance from the blast to the firing point, up to several kilometers, if needed. 3. Charging and firing with Electronic Detonators (Site programmed delays) – The electronic detonator ignition module has an assigned ID number held on the internal chip. The electronic detonator with leg wire for connections is provided on a spool (Fig – 3A). In setting-up the round to be blasted, the electronic detonator is inserted into the booster. This primer is then loaded into each borehole (Fig – 3C). Next, the borehole is loaded with the chosen blasting agent / explosives. Prior to stemming the borehole, the digital logger is hooked onto each leg wire and digitally checked for short circuits, open circuits, and operational integrity. Once this check has been made, the electronic detonator is assigned its timing value. All of this information is stored in the digital logger while the timing value is permanently stored into the integrated circuitry of the electronic detonator. After the programming procedure is completed, all of the electronic detonators are hooked together by connecting with in-line snap-type connectors (Fig – 3B). Once the wiring is completed the digital logger is connected to the blasting circuit for verifying the functionality of wired round. The logger then checks for firing line continuity, extra detonators, and for detonators that have faulty connections or no connections at all. The functionality check of each electronic detonator and the round(s) to be blasted by use of the digital logger serves as a circuit continuity check. The information is then checked against the blast plan. The logger is then connected to the blasting machine to download the blast information (Fig – 3D and 4). The blasting machine software fully verifies the system hardware, software and the integrity of the wired round. This information is displayed on the blasting machine screen before the blast can be armed and fired. The blasting machine will not arm the round until the


4


system operational check is completed and no errors are indicated. The blast site must be cleared prior to arming the round. Then the blaster can fire the round.

Fig - 3 In general, accurate and flexible timing allows blasters to make small hole-to-hole and row-torow changes to account for drilling inaccuracies. Adjusting the blast design to actual conditions can improve safety and fragmentation, which can cut costs by optimizing the loading and hauling cycle, increasing crusher throughput, and reducing the amount of oversize handling and secondary breaking. In addition, precise and variable delay timing manipulations enhances highwall stability and bench crest preservation, resulting in safer mines operations and also for reduction of blast induced ground vibration. These improvements allow for more accurate placement of boreholes for succeeding blasts. Optimization of the blast design to take greater advantage of the electronic detonators’ precision expands the blast pattern and reduces the explosive consumption without negatively affecting production. Electronic detonators generally are programmable in 1-ms increments and have delay accuracy (scattering) as small as ±0.5 ms.


5


Fig - 4 4. Electronic vs Pyrotechnic system - The differences between the two systems relating to the timing accuracy and those relating to the reliability of a blast are listed in Table - A: Table - A TIMING PYROTECHNIC INITIATION SYSTEM

ELECTRONIC INITIATION SYSTEM

1. Detonator accurate within a ±10% range

1. Detonator accurate to within ± 0.5 ms

2. Lead (delay) times on shock tube

2. No lead (delay) times on detonator connectors

3. Lead (delay) times on detonating cord

3. No lead (delay) times on harness wires

4. Limited delay timing scenarios available

4. Any timing scenario possible (incremental of 1 ms)

BLAST RELIABILITY PYROTECHNIC INITIATION SYSTEM

ELECTRONIC INITIATION SYSTEM

1. Detonator functioning unknown

1. Detonators functionality known

2. Shock tube functioning unknown

2. Detonator lead functionality known

3. Detonating cord functioning unknown

3. Harness wire functionality known

4. 100% Hook-up unknown

4. Assurance of 100% hook-up

5. Detonation functionality unknown

5. Initiating unit functionality known

As discussed earlier, the electronic detonators provide more accurate timing than the conventional pyrotechnic detonators which rely on the combustion speed of a pyrotechnic composition. The


6


timing accuracy capability of the electronic detonator allows for: (i) More efficient application of explosive energy, (ii) Improved rock fragmentation and size uniformity, (iii) Excavation productivity increase, (iv) Cost saving on excavation and downstream operations, (v) Improved public acceptance to blasting, (vi) An additional benefit of electronic detonators is the improved control of blast-induced vibration and airblast. 5. Techno-Economic benefits of electronic detonators at large mining operations - In an era where profits are constantly being eroded, mines are looking towards technology developments to assist them in solving mining problems and reducing mining costs. An emerging technology that could assist mines in becoming more cost effective is electronic detonators. The introduction of the high accuracy electronic detonator can be seen as the quantum leap in blasting science. For past few years, the spotlight has fallen on commercial use of electronic detonators and the extent to which the promise of precise and programmable timing can assist mines with their environmental and productivity problems. Thus, the blasting community, now, can become better equipped to improve upon the current approaches and methodologies of blast design. The accurately controlled sequence of blast-hole detonation is one of the most critical parameters having a direct impact on overall blast performance. In the beginning, quantifying the benefits of electronic detonators was confined to small test sites. These studies proved the accuracy and consistency of electronic detonator timing accuracy, improved fragmentation with subsequent productivity increases and relevant cost savings. The challenge was to implement electronic detonators at a large, full-scale production operation, such as dragline bench blasting, cast-blast etc. In this scenario the real effect and other benefits of electronic detonators will emerge. Now the good news is, in developed countries most of the blasts in larger operations are carried out with high accuracy electronic detonator with substantial techno-economic benefits. 5.1. Significance of accuracy of delay timing in large mining operations: In a blast, explosive energy has to both break and displace the rockmass in which it is applied. Its effectiveness is directly proportional to the effective burden the energy must overcome. This relationship is crucial in basic blast design. Any variation in blast-hole detonation timing that would result in a hole being fired prior or after its nominal firing time will result in burden to energy relationships that will have adverse effect on blast performance. In large scale mining, the delay timing of blast-hole firing has a direct impact on, (i) Resultant fragmentation, (ii) Percentage throw achieved, (iii) Level of vibrations generated and (iv) Level of noise generated. The pyrotechnic detonator design is such that the average scatter of delayed firing is ±10%. This implies that for a blast-hole that should fire at 25ms from initiation, might fire at 22.5ms or 27.5ms. This may not seem like a huge variance, but the resultant effect is. The scatter on a 500ms delay detonator will cause it to fire anytime from 450ms to 550ms i.e. a range of 100ms. If taken into account that inter-hole delays of 10ms are used on a blast, out of sequence hole firing is almost guaranteed. The long awaited arrival of a high accuracy electronic detonator provides new opportunities to the explosive end user. The blasting community can become better equipped and able to improve upon the current approaches and methodologies used in blast design. The dramatic progresses in blasting technologies can be witnessed in last few years. The quality and performance of products have been improved substantially. The high accuracy detonator brought with it new meaning to one of the fundamental aspects of blast design; accurate controlled sequence of blast-hole


7


detonation is one of the most critical parameters that have a direct impact on overall blast performance in many ways. In fact, the potential effectiveness that the available explosives energy has to both break and displace the rock mass is directly proportional to the effective burden that energy must overcome. This relationship is a crucial element in basic blast design. An accurate controlled sequence of blast detonation is a fundamental design parameter having a major direct effect on overall blast performance. Any variation in hole detonation timing results in that hole being fired prior to or after its nominal firing time. The hole-to-hole detonation could still remain properly sequenced, or holes could potentially detonate totally out of sequence. This will result in burden to energy relationships that can have adverse impacts on the performance of a blast. The results of these impacts are generally witnessed as: (i) Poor rock fragmentation, (ii) Large amounts of oversize, (iii) High ground vibration levels, (iv) High air blast levels, (v) Flyrock incidents, (vi) Increased need for secondary blasting, (vii) Increased excavation and crushing costs etc. Studies have shown that accurate blast-hole detonation would provide effectively minimise these adverse timing related impacts. These studies proved the electronic detonator in terms of: (a) Detonator accuracy, (b) Vibration prediction and (c) Rock fragmentation. 5.2. Challenges and strategies for introduction of Electronic Detonators in large mining operations - The challenge lies now in the introduction of electronic detonators on a full-scale production environment of large opencast operations. The primary objective of any large scale opencast operation to use electronic detonators is the possibility of reduction of overall costs. Generally, drilling and blasting costs form one of the major components of any larger opencast mine’s cost structure i.e. about 35% of the total consumable cost. More efficient application of explosives implies less overall drilling & blasting cost to create at least with the same results as with pyrotechnics in terms of fragmentation. Initially, the basic strategy of implementation of electronic detonators in any bigger opencast operation should be to start the use of electronic detonators on exactly the same parameters pertaining to pyrotechnic detonators at the time. Results and performances of each blast are to be evaluated and on the basis of continuous improvement, and gradual small changes are to be made at a time. This process to be repeated through a few stages until an optimal result is achieved. Data in terms of blast performance, dragline productivity and costs are to be captured throughout the process. This information forms the basis of the analysis and stands proof for claimed improvements. Although, while implementing, the focus has to be on cost saving, improvement in terms of vibration and airblast are also to be established. Ironically, the improvements in terms of ground vibration and airblast can not be quantified in terms of cost, but the effects can be measured by a seismograph and benefits can be felt from the surrounding mine environment and neighbouring structures. 5.2.1 Monitoring of blast performances – During trial with Electronic Detonators, blast performances are to be monitored and advantages should be established on following fronts. (a) Improved Fragmentation - Fragmentation results are to be analysed after the blast. For this purpose software packages such as Wipfrag or Split may also be employed. Fragmentation analysis delivers results in terms of relevant fragment sizes, or the improvements thereof. However, there is no need to prove improved fragmentation, as it is visually analysed and benefits are evident from handling, excavator throughput, crusher throughput, transport etc. (b) Increased machine productivity - Dozer and dragline productivity form part of the day to day operational controls of a large mine. Generally, mine management take decision to


8


investigate the resultant effect of improved fragmentation, i.e. improved dozer and dragline productivity and in all the cases where such field trials conducted observed substantial benefits in operational productivity including reduction of cycle time. In one such case the improvement observed in dozer productivity is about 17% and improvement in dragline productivity is about 8%, with a 5% reduction in overall cycle time. (c) Reduced drilling requirement – Large production mines generally face blasting material inventory constrained because of their high production target. This implies that they do not have enough drilled inventory in the field as compare to the target given. The process of implementation of electronic detonators in a high production mines should be in various stages. The drill patterns are to be increased gradually and thereby pressure on drill inventory is eased and subsequently shortages of availability of blasting material are reduced. As an example, in Table – B shows, while carrying out trials with Electronic Detonators changes made on overburden drill patterns in a dragline block of a high production opencast coal mines and the effect it had on the drilling requirement for a block length of 300m (South African opencast coal mines). Table - B PARAMETER

STAGE 1

STAGE 2

STAGE 3

Pre-split Spacing (m)

4

4

4

Stand-off from pre-split (m)

3

3

3

Depth of hole (m)

32

32

32

Dia. of hole (mm)

260

260

260

Burden (m)

7

8.3

10

Spacing (m)

9

10

11

First-row spacing (m)

7

8.3

9

Stemming length (m)

4

4

5

Number of rows

6

5

4

Number of holes

285

233

196

Percentage change relative to Stage 1

---

-18%

-31%

The substantial improvement in blasted inventory observed after changes in blast pattern with the same number of drill machines. (d) Reduced explosive cost – By increasing the drill pattern (as of Table – B) the number of holes in a blast block is reduced. This implies a higher powder factor (keeping the explosives quantity same per hole), i.e. more cubic meter of waste material blasted per kg of explosives used. Thus, with better and precise delay timings the explosive cost of blasting has been reduced. The reduction of cost was about 30 to 35 percent from stage 1. (e) Reduced vibration and airblast - There are many variables and site constants involved that collectively result in the formation of a complex vibration waveform. Providing a well designed


9


blast plan and the application of proper field controls during all steps of the drilling and blasting operation help to minimize the adverse impacts of ground vibrations. The design should consider the proper blast-hole diameter and pattern that reflect the efficient utilization and distribution of the explosive energy loaded into the blast hole. Blast design also provides the appropriate amount of time, i.e., delay between adjacent holes in a blast to provide the explosive the optimum level of energy confinement. The parameters having the greatest effect on the composition of the ground vibration waveform are (i) Geology between the blast site and the monitoring location and (ii) Accurate timing between blast holes in a detonation sequence. Thus, it has been observed, incorporating accurate delay timings with the help of electronic delay detonators substantial reduction in blast induced vibration and airblast occurrences take place. 6. Structural response to blast-induced ground vibration - Structural response to blastinduced ground vibration is a phenomenon that has been analyzed for many years. It is becoming increasingly important, from an environmental viewpoint, to minimize vibrations induced in urban dwellings by blasting. Research developed by the USBM, universities, and others over the last more than two decades in the blasting industry, has concluded that a residential structure’s level of response to blast induced ground vibration is dependent on both the peak particle velocity and the frequency of the waveform. The frequency is the number of oscillations that the ground particles vibrate per second as a blast vibration wave passes by the structure’s location. Researchers have shown that, above ground structures resonate whenever they are excited by a vibration containing adequate energy matching the fundamental frequency of the structure. The value of this frequency is mainly dependent upon the mass, height and stiffness of the structure. The maximum response of a house to blast induced ground vibration occurs whenever the frequency of the ground vibration matches the natural resonant frequency of the house. Likewise, if there is little or no energy at the resonant frequency of the structure, the structural response to the vibration will be negligible. When a structure is given an initial disturbance, it will vibrate at one or more of its natural frequencies, which are controlled by its mass and stiffness distribution. The highest frequencies of the system are always the multitude of the fundamental frequency. These characteristics in a structure are the controlling factor in response to a dynamic load such as ground vibration induced by a blast. There are two methods that can be used to calculate the dynamic properties of a structure. One of these methods is by theory (Computer Modal Analysis) and the other is by experiment (Frequency Response Function). ‘Computer Modal Analysis’ is done by entering into a computer the physical dimensions and the geometric and physical material properties of a structure. By adding vibration induced from traffic, blasting, construction or natural phenomena the model's response can be calculated. Whereas, ‘Frequency Response Function (FRF)’ is an experimental technique used to calculate the dynamic properties of a structure. This technique is widely used in different industries to solve many types of dynamic problems, such as structural failure, noise and vibration. Generally, in order to calculate the FRF of a system, the system needs to be excited with some kind of a signal. This signal is called an input signal. The input signal would be a ground vibration at the foundation of the building and the structural response to the ground vibration is the output signal. To calculate the FRF of a structure, ground vibration is generated and measured simultaneously with structural response. To do this, vibration sensors are placed on the structure and the ground. Ground vibration can be generated by detonating a small amount of explosive buried in the ground near the structure. 6.1. ‘Signature-Hole’ Blast Analysis for Vibration Control by using Accurate Delay Timing Electronic Detonator System – A method of controlling blast vibrations other than by modifying the scaled distance came into use some time ago. The crucial point of the methodology


10


is the use of a pilot-blast signal which takes account of the seismic properties of all complex geology between the blast and the target locations. Therefore, it does not require any geological model or assumption. The analysis illustrates how the delay interval between blast-holes can be chosen to control and minimize the vibration energy within the structural response band of most houses. Research studies had indicated that blast vibration could be simulated by detonating a “Signature Hole” with the vibration monitored at critical locations, and then using a computer to superpose the waveforms with varying delays (Fig – 5). By choosing delay times (∆t) that create ‘destructive interference’ at frequencies that are favored by the local geology, the “ringing” vibration that excites structural elements in structures, houses and annoys neighbors could be reduced. In this method, accurate delay times are crucial to effective vibration control, scatter in the firing times limited the method severely. Electronic detonators have scatter less than a millisecond. In light of all these, researchers have started finding both limitations and new potential of this new technique of controlling blast vibration. Briefly speaking, in this system of analysis, a single hole test blast (signature hole) is detonated at the blast site. Blast sequence is simply defined as a series of single hole detonations that are separated by a given amount of time. It is the relationship between this time and the geology of the site that has the most effect on the amplitude and frequency composition of the ground vibration wave. This relationship between timing and geology has led to the development of several sophisticated computer programs to predict and modify blast induced ground vibrations. These programs process a single hole blast ground vibration signature at a given production blast location, and through thousands of mathematical iterations predict and simulate the synthetic waveform, its amplitude and frequency composition for any given delay timing between adjacent holes in a row and between consecutive rows in a blast. The “Fourier Frequency Spectrum Analysis” of this blast indicates about ‘dominant frequency characteristic’ at the recording sites. The computer analysis determine the application of delay timing between holes, between the rows and between the decks which would produce the most favorable blast induced vibrations for structures and urban dwellings. In other words, “Signature Hole Analysis” is a modeling technique is to help control adverse effects of blast induced vibrations. The process involves controlling the frequency content by adjusting delay times within a blast containing several explosive charges. The risk to adjacent structures is thereby mitigated. Thus, with the growing adoption rate of electronic initiation systems as a tool to control nuisance of vibrations, the modeling techniques are becoming more popular. The introduction of a high accuracy electronic detonator into the commercial explosives market has had many positive effects in the area of predicting and controlling blast induced ground vibrations. It has been observed that without the implementation of electronic detonators the above software techniques are very ineffective. It has also been reported that, the timing designs by above technique with electronic detonators produces blast with a distinctively shorted duration. This coupled with the higher dominant frequency content of the vibrations reduces the amplitude of structural response. Instantel has recently developed and launched a ‘Signature Hole Analysis’ software tool, which allows users to simulate a large number of charge delay times very quickly. The software, in fact, is a modeling technique used to help control blast induced vibrations.


11


Fig – 5 6.1.1. Advantages of the technique, ‘Signature Hole Blast Analysis’, for Vibration Control This technique provides optimum electronic timing while maintaining high level of production with efficiency by raising quantity of explosives per delay (kg/delay) and provide overall structural safety of blast surroundings. Moreover, blast with shorted duration results in mitigating effects of blast induced vibration. Therefore, as post-blast vibrations are reduced by raising frequencies, much larger blasts can be undertaken with better operational performance, without compromising stringent safety standards of environment. Thus, Signature Hole Analysis software tool available can be used to help optimize and improve overall operational efficiency. It has also been observed that this vibration control method is feasible for underground mining ring blasts as well. Thus, the occurrence of electronic detonators and development of computer sciences brought a new expectation in controlling the vibration level and, hence, carry out bigger blast operations both in surface and underground operations. Today electronic detonation has transformed


12


production efficiency in mines by allowing larger blast blasts to handle, improving blasting cycle efficiency with enhanced safety and lesser ore dilution. 7. Blasting safety and opportunities - The greatest advantage of this detonator type is its safety against any stray currents, radar radiation or other electromagnetic interference (EMI) and its safety against misuse. It cannot be fired simply by a battery or other electric sources. a. The electronic delay detonators address the following security concerns in relation to safety: i) Unique ID no. of the detonator which is assigned by the manufacturer will enable to trace supply chain from manufacture to the end user; ii) Programmable delay timing; iii) Can be initiated only by authorized blasting machine after feeding all the data. Thus, it will prevent misuse of the detonators by antisocial elements. b. Blasting Opportunities with Electronic Detonators are: (i) Frequency Control / PPV Control, (ii) Large Open Pit Patterns - Casting/Long Delays, (iii) Air Decking, (iv) Multiple Decking - Minimal Delay Intervals, (v) Drifting - Standard Delays / Dual Delay Units, (vi) Large Stope Blasting, (vii) Smooth Wall Blasting, (viii) Fragmentation Optimization, (ix) Delay Period Re-Evaluation 8. Conclusion – Although the electronic blasting systems observed have an unparalleled safety feature, since they cannot be initiated by a conventional blasting unit.; electronic detonators can still be initiated by lightning, fire, and impact of sufficient strength. It is anticipated that a decrease in the number of pre-detonations, misfires and other unintentional initiations should result from the use of electronic detonator systems. Moreover, since Digital Delay Initiation System controls vibrations efficiently, there are much less concerns now about the impact of blasts affecting communities surrounding the mines. Because of the various advantages discussed, Digital Initiation System is steadily replacing signal tube detonators as the initiation system for explosives blast in larger mines. References: 1. Atlas Powder Company, Dallas, Texas, USA - “Explosive and Rock Blasting” 1987. 2. Langefors, U & Kihlstom, B.K. – ‘The Modern Technique of Rock Blasting’, John Willy & sons, 1963. 3. Sharma, P.D.; - ‘Controlled Blasting Techniques – Means to mitigate adverse impact of blasting’; Procc. of 2nd Asian Mining Congress, organized by MGMI at Kolkata (India) dt. 17th – 19th January 2008 (pp: 286 – 295). 4. Dowding, Charles H.,1985,”Blast Vibration Monitoring and Control”, Northwestern University , Evanston,IL.


13


5. Nicholls., H.R., Jhonson., C. F. and Duvall., W.I., - ‘Blasting Vibrations and their effects on Structures’, USBM Bull. 656. (1971). 6. Sharma, P.D.; - ‘Electronic detonators – An efficient blast initiation system’, Mining Engineers’ Journal, India, October 2008. 7. Watson., John. T; – ‘Developments with Electronic Detonators’, Proc., of Int. Conf. On Expl. & Blasting Tech, ISEE (2002). 8. Sharma, P.D.; - ‘Enhancement of drilling & blasting efficiency in O/C & U/G mines – Use of modern precision drilling, electronic delay detonator system and other sophisticated equipments with new generation emulsion explosives are the need-of-the-hour’; Mining Engineers’ Journal, India, February 2007. 9. Siskind ,D. E., Stagg, M. S. ,Kopp, J.W., Dowding, C.H.,1980, - ‘Structure Response and Damage Produced by Ground Vibration from Surface Mine Blasting’; Bureau of Mines RI 8507, OSM Dept. of Interior Washington, DC. 10. Medearis, K., 1976, “ Development of Rational Damage Criteria for Low Rise Structures Subjected to Blasting Vibrations”, Report to the National Crushed Stone Association, Washington, DC. 11. Sharma, P.D.; - ‘Electronic detonators – Results in substantial techno-economic benefits for large mining operations’, Mining Engineers’ Journal, India, February 2009. 12. Doglus,A. Anderson.; - ‘Signature hole blast vibration control – Twenty years hence and beyond’, The journal of Explosives Engineers, September / October 2008 (pp. 8 to 12). 13. Christopberson, Pappilon, - ‘Vibration reduction through production – signature hole blasting’, The journal of Explosives Engineers, September / October 2008 (pp. 16 to 20). 14. Instantel: http://www.instantel.com/newsletters/jfr/jfr_q2_2008.pdf 15. Signature Hole Blast analysis Technique: http://www.scribd.com/doc/13239794/SignatureHole-Blast-Analysis-Control-Blast-Induced-Ground-Vibration 16. Electronic Detonator: http://www.scribd.com/doc/13240393/Electronic-Detonators 17. Sharma, P.D.; - ‘Open pit blasting with in-hole delays and / or pre-splitting of production blast – Measures to control adverse impact of complex vibration arising due to presence of underground workings in the vicinity or in otherwise sensitive areas’; Mining Engineers’ Journal (MEAI), August 2006. 18. http://knol.google.com/k/partha-das-sharma/programmable-digital-detonatorsystem/oml631csgjs7/28 19. Programmable Electronic Detonator: http://www.scribd.com/doc/15500918/ProgrammableElectronic-Detonator --------------------------------------------------------------------------------------------------------------------


14


Appendix Safe Practices while dealing with Electronic Detonators: ALWAYS follow manufacturer's warning and instructions; especially hook-up procedures and safety precautions. ALWAYS fire electronic detonators with the equipment and procedures recommended by the manufacturer. ALWAYS verify the detonator system integrity prior to initiation of a blast. ALWAYS keep the firing circuit completely insulated from ground or other conductors. ALWAYS use the wires, connectors and coupling devices specified by the manufacturer. ALWAYS follow the manufacturer's instructions when aborting a blast. Wait a minimum of 30 minutes before returning to a blast site after aborting a blast unless the manufacturer provides other specific instructions. ALWAYS clear the blast area of personnel, vehicles and equipment prior to hooking up to the firing device or blast controller. ALWAYS keep detonator leads, coupling devices and connectors protected until ready to test or fire the blast. ALWAYS keep wire ends, connectors and fittings, clean and free from dirt or contamination prior to connection. ALWAYS follow manufacturer's instructions for system hook-up for electronic detonators. ALWAYS follow manufacturer's recommended practices to protect electronic detonators from electromagnetic, RF, or other electrical interference sources. ALWAYS protect electronic detonator wires, connectors, coupling devices, shock tube or other components from mechanical abuse and damage. ALWAYS ensure the blaster in charge has control over the blast site throughout the programming, system charging, firing and detonation of the blast ALWAYS use extreme care when programming delay times in the field to ensure correct blast designs. Incorrect programming can result in misfires, flyrock, excessive airblast and vibration. NEVER mix electronic detonators and electric detonators in the same blast, even if they are made by the same manufacturer, unless such use is approved by the manufacturer. NEVER mix electronic detonators of different types and or versions in the same blast, even if they are made by the same manufacturer, unless such use is approved by the manufacturer. NEVER mix or use electronic detonators and equipment made by different manufacturers. NEVER use test equipment and blasting machines designed for electric detonators with electronic detonators. NEVER use equipment or electronic detonators that appear to be damaged or poorly maintained.


15


NEVER attempt to use blasting machines, testers, or instruments with electronic detonators that are not specifically designed for the system. NEVER make final hook-up to firing device or blast controller until all personnel are clear of the blast area. NEVER load boreholes in open work near electric power lines unless the firing lines and detonator wires are anchored or are too short to reach the electric power lines. NEVER handle or use electronic detonators during the approach and progress of an electrical storm. Personnel must be withdrawn from the blast area to a safe location. NEVER use electronic detonator systems outside the manufacturer's specified operational temperature and pressure ranges. NEVER test or program an electronic detonator in a booster, cartridge or other explosive component (primer assembly) before it has been deployed in the borehole or otherwise loaded for final use. NEVER hold an electronic detonator while it is being tested or programmed. -------------------------------------------------------------------------------------------------------------------Author’s Bio-data:

Partha Das Sharma is Graduate (B.Tech – Hons.) in Mining Engineering from IIT, Kharagpur, India (1979) and was associated with number of mining and explosives organizations, namely MOIL, BALCO, Century Cement, Anil Chemicals, VBC Industries, Mah. Explosives etc., before joining the present organization, Solar Group of Explosives Industries at Nagpur (India), few years ago. Author has presented number of technical papers in many of the seminars and journals on varied topics like Overburden side casting by blasting, Blast induced Ground Vibration and its control, Tunnel blasting, Drilling & blasting in metalliferous underground mines, Controlled blasting techniques, Development of Non-primary explosive detonators (NPED), Signature hole blast analysis with Electronic detonator etc. Currently, author has following useful blogs on Web: • http://miningandblasting.wordpress.com/ • http://saferenvironment.wordpress.com • http://www.environmentengineering.blogspot.com • www.coalandfuel.blogspot.com Author can be contacted at E-mail: [email protected], [email protected], ---------------------------------------------------------------------------------------------------------Disclaimer: Views expressed in the article are solely of the author’s own and do not necessarily belong to any of the Company. ***


16

Programmable Electronic Detonator

Recommend Documents