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Explosives Today - Series 4, No 6

quarry. With an increase of accuracy in the initiating system, better control over the blast results are achieved.

The movement and shape of the muck pile can be better controlled if the timing of the blast is more accurate.

The average tolerance of electronic detonators is 0.01 %. Pyrotechnic detonators have a tolerance of up to 3% and best case of 1% (at a price).

The precision of AEL’s electronic delay detonators provides the accuracy of that is unrivalled, with the detonator having a variation or a Timing Coefficient of Variance (CoV) of 0.01%. The use of Pyrotechnics with a CoV of 3-10% which results in poor management of limiting the levels of vibrations due to the inherent delay scatter built in the device design as a result of the chemical composition of the delay element. Civil and quarrying operations are generally found near developed areas thus requiring very stringent laws that manage and prevent civil law suits taking place.

Precision timing that is offered by electronics, single hole firing control managed by the software, and controlled mas per delay allows the user to adhere to the laws that govern the allowable vibration induced by

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blasting. The electronics system also allows for easier deck charging.

The delay scatter of pyrotechnic detonators have led to poor control with regards to cut offs, poor fragmentation results and multiple holes firing at once. Instead of limiting the mass/delay of the explosives, there could be 2 or more detonators firing at the same time (not as planned) and could cause potential fly-rock, high vibrations and air-blast incidents. Using electronic detonators reduces this risk.

Improved pit conditions There are a number of advantages of using electronic detonators which contribute to the pit conditions like slope stability. Controlling the mass/ delay by single-hole firing, the amount of energy propagation is reduced which in turn will cause less overbreak. In addition the direction of this energy can be controlled (with sequential firing of holes) which reduces the energy going back into the high wall. The stability of the high wall can be better controlled by using electronic detonators.

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Conclusion The initial cost of electronic initiation systems may seem high as compared to pyrotechnic initiation systems. The downstream cost savings that are realised make the initial investment seem negligible.

Mining companies are always trying to improve the safety of their workers.

Electronic detonators contribute to the safety with all the safety benefits without compromising production.

Electronic detonators will improve the production rates by achieving better blast results.

AEL Mining Services Explosive Engineers based at the regional offices are available to help and advise on the use of electronic detonaotrs for all blasting senarios.

Electronic Detonators

Nico Alberts, Explosives Engineer References: Carlos Goncalves – AEL Electronics Initiation Systems Product manager Ashlin Pillay – Field Technician Initiation Systems This document is a new addition to the Explosives Today series.

Disclaimer: Any advice and/or recommendations given by AEL Mining Services Limited (“AEL”) in this publication, is given by AEL in good faith in order to provide assistance to the reader. AEL does not however: 1.1warrant the correctness of its advice and/or recommendations; 1.2 warrant that particular results or effects will be achieved if AEL’s advice and/or recommendations are implemented; 1.3 accept liability for any losses or damages that may be suffered, as a result of a party acting, or failing to act, on the advice and/or recommendations given by AEL;1.4 accept liability for any acts or omissions of its employees. representatives and/or agents, whether negligent or otherwise.

Copyright: All copyright that subsists in this publication together with any and all diagrams and annexures contained herein, which shall include all and/or any ideas, plans, models and/or intellectual property contained in this document vests in AEL. Any unauthorised reproduction, adaptation, alteration, translation, publication, distribution or dissemination (including, but not limited to, broadcasting and causing the work to be transmitted in adiffusion service) of the whole or any part of this document in any manner, form or medium (including, but not limited to, electronic, oral, aural, visual and tactile media) whatsoever, will constitute an act of copyright infringement interms of the Copyright Act No.98 of 1978 and will render the transgressor liable to civil action and may in certain circumstances render the transgressor liable to criminal prosecution. This document remains the intellectual property of AEL. Intellectual Property: All ideas, concepts, know-how and designs forming part of this publicationbelong to AEL, save for where it is clearly indicated to the contrary.

AEL Mining Services Limited (PTY) Ltd 1 Platinum Drive, Longmeadow Business Estate North Modderfontein, 1645 Tel: +27 11 606 0000 www.aelminingservices.com

Mining in the 21st century has moved away from just being driven on production volumes regardless of the costs. Today the mining sector demands a “bang for their buck”, in other words how can mining be done effectively and efficiently with minimal cost and risk whilst maintaining the highest standards of safety.

Electronic initiation systems were introduced to improve the safety of the mining operations and to provide accurate timing and sequential firing.

This consequently eliminates the timing scatter that is present in pyrotechnics.

It offers numerous economic benefits as well as environmental benefits, which is becoming increasingly important globally. In addition, these electronic initiation systems present significant improvements to the mining and milling efficiencies. These benefits include: − Improved pit conditions − Increased cast − Controlled environmental impact on sensitive areas − Fragmentation − Larger drilling patterns may also be implemented.

The technological advances in the mining industry have improved in

leaps and bounds in the recent years with numerous benefits. Effective blasting and achieving the correct fragmentation directly affects the profitability of a mine, the crusher throughputs and the digging rates. The implementation of electronic initiation systems and software aided packages is to improve the blasting process and the safety of working with explosives.

How does it work?

Electric Detonator: The conventional way of initiating such a detonator was by purely adding battery power (DC Voltage) which in turn will heat up the resistance wire.

The resistance wire will then produce enough heat to start the initiation of the primary charge (base charge) in the detonator. This was a very effective way

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of initiation of explosives, but with the ease of use also came danger.

The resistance wire in the detonator is very thin and does not need a lot of energy to initiate the very volatile mixture of explosives that makes up the base charge. When a RF signal like 2-way radios or cell-phones are within a certain distance of an electric detonator, induction will occur.

This is the same way a magnet will induce an electrical current when passing by an electrical wire. In certain cases it was also mentioned that as little as a normal 9V battery could initiate an electric detonator.

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Electronic Delay Detonator

Fuse Capacitor Head

Firing Signal & Firing Voltage Lead Wire

Earth Spike

For an electronic detonator, typically an integrated circuit and a capacitor system internal to each detonator separate the leg wires from the base charge, and depending on the design features can greatly enhance safety and timing accuracy (See Figure 1). This system is obviously a more complex design compared to an electric detonator or shock tube detonator.

A specially designed blast controller unique to each manufactured system transmits an encrypted digital signal to each wired electronic detonator. The signal is identified by each electronic detonator and the detonation firing sequence is accurately assigned.

Electronic detonators perform unlike electric detonators as the electronic detonator requires a blast voltage and a coded firing signal that is generated within a Smart blast key.

Microchip

Pyrotechnic Detonator

Sealer Crimp

Crimp

Shock Tube

Bushing

Isolation Cup

Electronic Detonator:

Electronic detonators have been designed to eliminate the pyrotechnic delay train that is a component of electric detonators and shock tube detonators, thus improving timing accuracy and safety.

Primary Charge

mechanical key is not in place, the system will not initiate the detonator.

It is like having a circuit breaker.

Base Charge

Primary Charge

Delay Train

Base Charge

Figure 1: Electronic Detonator vs Pyrotechnic Detonator

Safety Current electronic detonator systems offer various sophisticated safety features, which have become a basic requirement for the technology. In countries where detailed approval testing and certification is required, complying with these safety aspects is a prerequisite to use.

Extremely detailed research has formed the basis for the establishment of strict standards of compliance in South Africa (SANS1717-1), Europe (CEN/TS 1376327) and Canada (CEAEC).

The common standard safety protection afforded by electronic detonators relates to: − Inherent safety − Electrostatic discharge (ESD) protection − Over-voltage protection − Electromagnetic immunity

Testing & Testing Equipment By using electronic detonators, the safety in blasting practices greatly improved. Unlike pyrotechnic detonators

like ShockTube or Fuse/ignitor cord assemblies, electronic detonators can be tested for functionality before the blast.

If a faulty unit is discovered, it can be replaced right away in turn reducing the probability of a misfire.

Specialised Control Equipment is used to test and initiate the detonators. The words “Inherent Safety” is used when describing the test equipment. That means that there is absolutely nothing that would make the test equipment accidentally initiate the detonator.

Users of the system can easily test the detonators without the possibility of initiation.

Mechanical interlocks The latest versions of electronic detonators available to the market also have electrical and mechanical interlocks that must be in place for initiation to occur. By use of Blasting Keys, Firing Signals and High Voltage, the user can be assured that the system will not prematurely detonate the detonators. The Blasting Key is not only an electrical connection but a mechanical one as well. If the

Please note: Normal safety procedures are still in place. As per mine regulations 2-way radios and cell-phones are not to be used when closer than 1m from an electronic detonator and 5m from electronic initiating systems control equipment as these are the minimum distances to enable full system functionality.

A complex digital firing sequence with numerous replies and confirmations that cannot be reproduced by naturally generated electrical impulses is required to initiate the blast. Sufficient energy must be available from the storage capacitor to fire the fuse head.

The transient nature of ESD makes this impossible due to the length of time required to charge the capacitor through the detonator protection circuitry.

In recent years we have seen in increase in ATM bombings. An electric detonator will be used to blast the machine open and the cash in the machine are then taken resulting in not just the loss of the cash, but also a huge financial cost to replace or repair the ATM. And we wonder why banking costs are so high...

The chances that an electronic detonator is used for an ATM bombing are slim to none. The main reason is because the detonator can only be initiated by the matching control equipment. If the user can get their hands on a set of the control equipment, there is also a “Blasting Key” which is password protected.

The Blasting Key also produces the “Firing Signal” which will tell the detonator to fire. As mentioned earlier, a certain voltage is needed to accompany the Firing Signal to ensure detonation. This combination of safety features will make it less likely for an electronic detonator to be used for ATM Bombings.

Over-voltage and electrostatic discharge Over-voltage protection governs protection against initiation from the deliberate or accidental connection of high electrical output devices such as

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mains current, electric detonator shot exploders, cap lamps, batteries and lightning to an electronic detonator.

This test is included in the South African standard of compliance (SANS 1717-1) due to incidences with electric detonators but is not included in the European Standard (CEN/TS 1376327).

Over the past two years it has been reported that a total of three separate blasts at different mining operations globally which all used the shot detonators were struck by direct lightning strikes but did not cause any premature initiations. However substantial damage was caused to a number of the detonators electronic circuitry which caused the units to become non responsive after the lightning storm had lapsed. To date since the introduction of electronic detonators from AEL, there has not been a single premature detonation due to a lightning strike!

Electrostatic charges and their resulting discharges can be found in everyday life. When concentrated on equipment or individuals to a high enough level, static can create electric shocks – e.g. touching a metal door knob after walking on nonconductive carpeting. ESD can create serious risk of ignition of explosives powders within a detonator. It can also damage electronic components such as microchips, circuit boards, etc. that are found in electronic detonators.

The solution, therefore, is to ensure adequate ESD protection within detonators. To do this, preferential discharge paths are deliberately included in the electronics module to steer any discharge away from the fuse head and sensitive explosives compositions.

Resistance to dynamic shock (sympathetic detonation) Another problem that occurs is that one hole might sympathetically detonate an adjacent hole. This

n=0.75 Graph 1. “S” curve – Non-elctric vs. Electonic

n=1.50 Figure 3. Mean size vs. Uniformity

usually happens when the burden and spacing of the pattern is too small, or when the deviation of the adjacent holes is tending towards its other.

Detonators are usually the weak link in this situation but AEL’s electronic detonators has a resistance to this type of shock and is less likely to sympathetically detonate.

Improved Uniformity in fragmentation results In the mining industry there is always a drive to improve profits, the less it costs, the better. Unfortunately that is almost never the case. Buying cheap can sometimes cost you more.

As with many other products used in the mining industry, there are

Figure 4. Scatter of pyrotechnic delays compared to electronics

inexpensive items and more expensive items. The same applies to initiating systems. The trick is not to look at the initial cost, but at the down-stream cost saving. Many studies have been done to prove the down-stream cost saving when using electronic detonators.

A misconception with the use of electronic detonators is that it will reduce the fragmentation size of your blasted rock. This is NOT true.

Electronic detonators will make your fragmentation more uniform if applied correctly. If the fragmentation size has to be changed, the amount explosives mass applied in a volume of rock has to be changed (Powder factor).

If the blasted rock has a more uniform fragmentation, it means that more of the rock is useable and more rock will pass through the crusher (depending on the size). There is also a reduction in oversize rock which in turn will reduce the cost of secondary blasting.

In figure 3, the mean size (Xc) of the rock is the same. The uniformity index (n) however has been changed.

The S-curve in Graph 1, shows the results of the Electronic Detonators against the results of Pyrotechnic Detonators.

Accurate firing harnesses the energy of the neighbouring holes (crack propagation during explosive reaction)

to effectively contribute to the rock breaking process. The smaller the delta value between the 20% and 80% passing, results in a more uniform fragmentation.

Digging rates and loading factors are also increased when using electronics. The shape and position of the muck pile can be controlled with the timing of the blast. If electronic detonators are used, a blast can be designed more accurately so that the muck pile is optimal for the loading equipment.

Timing Accuracy Accuracy in the timing of a blast is of great importance to every mine or