December 2016

Detonators – best-for-project practices in drill and blast

  • By Michael Wiseman, Technical Services and Stephen Timbrell, Blasting Specialist, Action Drill & Blast

Developments in detonation systems have the potential to improve blast capability and productivity

As the mining industry becomes increasingly lean, a ‘one size fits all’ approach is becoming increasingly obsolete. A commitment to continuous improvement – finding ways to do things better, faster and more cost effectively – is how asset owners and contractors are ensuring their ongoing success.

In drill and blast, developments in detonation systems have provided forward thinkers with an opportunity to dramatically enhance their blast capability. Highly tailored blasting solutions, with the potential for significant cost and productivity benefits, are now being implemented by many teams and contractors who have been willing to invest in increasing their knowledge base, trialling new electronic initiation technologies and upskilling.

An introduction to electronic systems in the Australian mining industry

Prior to the 1990s, pyrotechnic detonators, also known as electric and non-electric detonators, were the most commonly used in the Australian mining industry.

In the late 1990s, electronic initiation systems were introduced through a variety of explosive suppliers. Initial uptake was slow, but as the technology evolved and advanced to address the recognised practical limitations and to meet the specific needs of the end user, uptake progressively increased.

In these early years, the largest consumers of electronic detonators were underground and open pit coal mines. These projects could realise an immediate benefit to their operation because pyrotechnic detonators did not offer a solution to the problems associated with these types of projects, such as excessive ground vibration.

Today, through increased industry understanding, testing and delivery of tangible results demonstrating the benefits of using electronic detonators (covered in detail later in this article), they are now widely used across different commodities in both open pit and underground operations.

However, despite electronic systems’ proven benefits and advantages over conventional products in many blasting situations, a step-change is still required within some blast teams to overcome concerns, fully understand the technology and utilise it to its full potential to offer best-for-project solutions.

Addressing the barriers to uptake

Despite their advantages, the higher cost associated with electronic systems compared to conventional systems, along with the additional training required, still acts as a deterrent for many companies as there is not an immediately recognisable direct cost saving to the operational budget for drill and blast.

Further, it is well known that the majority of the cost benefits of using electronic systems are generally realised downstream via mining productivity and crushing throughput that are optimised through a continuous improvement program or series of site-specific trials, which also come at an additional cost to the project.

For many companies, the cost of changing to electronic technology is determined to outweigh the reward, which is not overly surprising in light of the current market conditions and the pressure to deliver immediate cost reductions.

Determining best-for-project

An electronic initiation system is not just about the detonator. While it is an integral part, all three elements of the system – the detonator, the blast planning software and the detonator programming hardware – provide the technology with its unique advantages.

Typically, electronic systems are best suited to:

  • projects in close proximity to vibration-sensitive infrastructure, such as houses, bridges, tunnels, rail lines and optic fibre telecommunication, where greater and more precise control over the blast is needed
  • large tonnage blasting where electronics can deliver cost efficiencies by reducing delay scatter, which will improve fragmentation and ultimately reduce the amount of bulk explosives required
  • projects where creating the muck pile profile to suit the digging fleet is the primary objective; for example, cast blasting using draglines and dozer push
  • complex blasts that have a requirement for multiple decks; for example, coal mining through seam blasting.

Productivity benefits of electronic systems

As discussed previously, most of the concerns around electronics can be overcome by investing in short-term training for long-term gain, smart technology selection and a change in mindset. It is essential to embrace innovation where it can be seen to deliver value.

The numerous benefits of electronics are discussed as follows.

Reduced bulk product use

This is electronics’ key advantage. The overarching goal for drill and blast is to use the raw energy from the bulk product to do the most useful work on the rock.

In most mines, the bulk product cost is more than all other drill and blast costs combined. Electronic initiating systems, when used to their potential, will achieve more with the rock using the same energy. Depending on the mine’s situation, this can deliver increased productivity or reduce costs by blasting the rock better so that it digs faster and the mine produces more for the same cost. Alternatively, if the mine is operating at full capacity, capacity can be maintained at reduced cost by doing the same work with less bulk product because the energy is being used more efficiently.

Cheaper at longer lengths

In a pyrotechnic detonator, the head of the detonator is relatively cheap and the tailwire is relatively expensive. In electronics, the head is very expensive due to its computer chips, but the tailwire is cheap as it is just wire. This means that short lengths of pyrotechnics are cheaper per detonator but at long lengths, usually greater than 50 m, electronics are cheaper.

Improved fragmentation

Most of the gains achieved with electronics are not made through the detonator itself but through the use of its advanced software. In just a matter of hours, a blast team has the ability to plan timing sequences that would otherwise take days using conventional equipment and be impossible to practically implement.

Even when using the exact same timing sequence across both systems, electronics deliver an advantage as the detonator is accurate to the timing it communicates (±1 ms), compared to the unavoidable natural variability (±5 to 25 ms, called ‘scatter’) in pyrotechnic initiation systems. This often results in smaller or bigger time gaps between detonations than expected or holes may even detonate in the wrong order.

However, the major benefit of the accuracy and flexibility of electronic timing capability is the ability to devise a plan that best suits the shot in question. Very fast, very slow and/or very complex sequences can be used to get the most useful work out of the explosives to achieve optimal fragmentation. Trying these sequences without electronics would be unsafe, impractical or impossible.

Reduced ground vibration

The best electronic initiating systems come with a vibration prediction tool so that vibration can be predicted at various points, particularly sensitive ones. This is called ‘time of arrival analysis’. The blast timing can then be modified to protect those points, and the vibrations can be aimed in a direction where nothing of value needs protecting.

Furthermore, because of the accuracy of the timing, the explosive energy is released at the exact time it was set to, meaning that there are no unplanned spikes in energy (and therefore vibrations).

Improved control of blast movement

As previously mentioned, electronic systems’ advanced timing make it possible to speed up and slow down certain parts of the shot to change the muck pile profile. A basic rule is that a hole that detonates a long time after the hole next to it will tend to move into the gap where the last hole was. It is possible to change the height of the pile and where the pile sits by changing the timing between the holes.

Integrated safety and security features

Pyrotechnic detonators have a very advanced and shielded fuse, but they can still be set off by anyone with the appropriate tools. Similarly, an electric system can be set off by stray electrical currents such as radios, lightening or mobile phones.

While each electronic system differs between suppliers, the firing box typically communicates with each detonator in the circuit via the internal microchip to check for continuity by using enough power to test the circuit but not enough to initiate the detonator. Any faults in the circuit are reported to the firing box. Once the firing box is armed and ready to fire, full power is delivered to the detonators to enable initiation. Additionally, because electronic detonators have a built in microchip, they have a unique serial number that can be tracked if required.

Reduced detonator stock requirements

Pyrotechnic detonators are a fuse, so the timing delay on the box is based on a very small fuse in the detonator. This means that a different detonator is needed for each timing. If different lengths of detonator are needed for each timing, a dozen or more different detonator piles might be needed, but only a couple of types will be used for each blast. With electronics, the timing is programmed in, so only different lengths are required. With less than half the combinations needed, twice the quantity of each length can be used in the same magazine.

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Technology on the market today

There are a number of different companies marketing products today, and everyone in the industry has their preference.

There are ‘single chip’ systems, where the same chip/capacitor that is used for testing is used for firing. This makes the product cheaper but also more pedantic when programming the detonators and more fragile as only so much energy can be sent during testing and programming.

Other products are more expensive but have arguably more robust dual chip/capacitor systems, where one chip is used for programming the blast and the other is used for firing it.

A smarter and more powerful programming chip enables more to be done automatically and robustly. There is no concern over sending too much energy to the chip and setting it off as the firing chip is only unlocked at firing time.

There is currently only one product available that has vibration modelling and muck pile shaping in its software. It is possible to instruct it to shift and lift in certain directions and protect areas. It can send the timing to the detonators and provide information on what impact that has vibration-wise on the sensitive points.

The timing programs for the other products are more manual and if they have vibration modelling, it’s generally only available at extra cost or by hiring the vendor’s technical team.

Best-for-project is key

Selecting technology based on what is best-for-project must be front of mind for any drill and blast team.

If the project is basic, using advanced electronic systems won’t realise any productivity or cost benefits when conventional products will perform what’s required.

On the flip side, an unwillingness to adopt electronic technology because of the perceived extra costs or training required – when the likelihood that the cost efficiencies gained in other areas of the project would outweigh the upfront capital expenditure – would be an unfavourable approach in any economy, and even more so in the current climate.

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