Pioneering achievement in surface blasting
The AEL Quickshot™ Centralised Blasting System – A Benefit Case Study in a Narrow Reef Mine

Background

The development of a centralised blasting system (CBS) began with one of the first narrow reef mines taking the initiative to blast electronic delay detonators (EDDs) on a large scale.

Once a number of working places had been fully converted and because of the useful information that was available to management directly after blasting, it became apparent that blasting all working places from surface was possible. Subsequent to a mine-wide conversion to EDDs, the centralised blasting system was successfully implemented.

The Blast Control Unit Centralised blasting System

The blast control unit (BCU) system came into being after addressing the legacy problems experienced by its predecessor, the cross-cut control unit (CCU) system.

Distinctive benefits of the AEL Quickshot™ BCU system include

• Improved seismic footprint with the aim of reducing fall of ground (FOG) accidents and also the effect that the uncontrolled seismic events have on the loss of available production faces and the cost and effort in the rehabilitation of these workings. (See graphs 1 and 2).
• Reduction in blasting and gassing incidents
• Improved lost blast rate. (See graphs 3 and 4)
• Reduction in human intervention – making the system more user friendly and at the same time reducing the user dependency of the system (See graphs 5,6)
• Energy saving by using relays to switch off mine services such as compressed air, water and power to the section at blasting time.
• Reduction in maintenance costs.

On completion of the BCU trials, the comparison of the two systems coupled to the benefits of the old system could be quantified.

Seismic Incidents

The mine converted to a fully electronic Centralised Blasting System with the purpose to use the available information to manage the use of the system, and maximise the benefit that the improved seismic footprint gives them relating to accidents and incidents. It was found that a seismic event followed directly after the blast.

The mine then launched an initiative to compare the historical seismic data of the already installed geophones with their current data. Findings showed that there was a definite change in the seismic patterns between the different sections of the mine.

Graph 1: Indicates the recorded Seismic Profile before Centralised Blasting was implemented.

It was also apparent that in areas blasted centrally, more seismic events occurred in the off-shift period directly after the blast than other areas of the mine that were not.

UnearthedGraph 2: Indicates the recorded Seismic Profile after Centralised Blasting was implemented.

The above graphs were compiled by the rock engineering department and show seismic activity over a 12 month period. From the graphs, it is evident that the time of greatest seismic activity is concentrated directly after the blast and before re-entry of the shift into the working places. By reducing this window of seismic activity, the mine is actively reducing the risk of exposing its workforce to highly stressed workings.

FOG Accidents

There is a significant correlation between seismic events and the FOG accident rate. It is acknowledged however, that Centralised Blasting is not the only influencing factor but that the types of support, mining configuration and rate of mining, as well as geological discontinuities also have an effect on these types of accidents.

The FOG accident rate recorded since 1999 indicates a downward trend in FOG related types of accidents (See graph 3) although one must be cognisant of the continuous drive to prevent these types of accidents. Initiatives include the improvement in support types, mining configuration and other implemented strategies. In general, it is believed that a fully Centralised Blasting System contributes to achieving these improvements in reducing FOG incidents.

Graph 3: Indicates the FOG accidents as recorded by the mine's safety department.

The FOG trend on the mine indicates a definite downward trend since the mine changed completely to Centralised Blasting.

Furthermore, no gassing or blasting accidents have been experienced since the Centralised Blasting System was introduced. This is mainly due to the fact that the Netshock™ electronic starters are inherently safe and can only be initiated by means of the designed control equipment and not by any other power source e.g batteries or caplamps.

Lost Blast Rate

According to a study done several years ago, the general lost blast rate was established at an average of a 4% baseline. Historical data on the lost blast rate indicates that a consistent improvement was achieved by the mine, in that the average lost blast rate hovers around a 1.0% target, which is a noteworthy improvement compared to the industry average of around 4%. (See Graph 4).

This translates to a significant saving when considering a conservative fixed cost figure of R80,000 per panel not blasted. Over a one year period, the mine sustained an average lost blast rate of 1.29% with the CCU system, which resulted in an average of 18 panels lost per month out of an average of 1381 panels blasted per month.

Graph 4: Indicates the recorded Lost Blast rate over a
12 month period after Centralised Blasting was implemented with CCUs.

The AEL Quickshot™ BCU system was designed to reduce the lost blast rate by eliminating the problems encountered with the previous system. Subsequently, the BCU system has achieved a lost blast rate of 0.74% measured over the last 10 months since the trial was conducted (See Graph 5).

Graph 5: Indicates the recorded Lost Blast rate over a 12 month period after Centralised Blasting was implemented with BCUs.

This resulted in an average of 4 panels lost per month out of an average of 443 panels blasted per month. (See Graph5)

During the BCU trial, one of the criteria required by the mine was that a marked difference in intervention rate must be achieved to reduce the manpower component managing the system. Furthermore, the mine wanted to achieve a consistency in the lost blast rate through an improved designed system that is more user-friendly and requires less human intervention.

Graph 6: Indicates a comparison between CCUs and BCUs as recorded during the trial period.

As can be seen from the recorded evidence (graph 6), it is obvious that the BCU requires fewer interventions when compared to the CCU system. The intervention rate can directly be coupled to the lost blast rate. The reason being that an intervention is usually the follow-up action after a lost blast was incurred. This reduction in intervention rate will automatically translate into a cost benefit to the mine in that fewer personnel are required, or the current personnel can be used to attend to other priorities.

Energy Saving

With the AEL Quickshot™ BCU system, mines have the flexibility to control auxiliary services such as compressed air, power and water from surface. The benefit of this function is that the control room on the mine can switch off these services during peak hours, usually when blasting takes place between 18:00 and 20:00. With the ability to control services from surface, the mine can isolate specific sections underground or all production sections, for instance, over long weekends or the Christmas break. Not only can the mine reduce its power consumption significantly, but also improve its energy efficiency (GJ/oz) and reduce its carbon footprint in the process.

Maintenance Costs

A detailed record of the CBS costs at the mine is being kept in order to measure the impact of changes to the customer. The costs include the salary of the blasting technician, purchasing of new equipment, repairs, transport costs, software cost and license fees. Consumables like Electronic starters and Fly-leads and extenders are also tracked as part of the operating cost reflected as part of explosive cost in the mine overseers' budget.

Currently AEL Quickshot™ BCU system is operating at 44% less than the CCU system due to fewer repairs being necessary.

Conclusion

As shown in this case study, there are proven results using the AEL Centralised Blasting System. The AEL Quickshot™ BCU system adds value to the customer's bottom line in all the expected areas. With further demonstration of these benefits not only in narrow reef mining, but also in shallower bord and pillar operations in platinum mining, the mining industry will soon be insisting on the widespread use of the BCU Centralised Blasting System.