The origins of “Explosives Today”Claude Cunningham

Then...

The 1960’s was a time of rapid evolution for blasting technology in South Africa. The sole explosives supplier, African Explosives and Chemical Industries Limited (AE&CI), operated the world’s two biggest explosives factories (at Modderfontein and Somerset West) and thrived chiefly on delivering dynamite and capped fuse systems to the nation’s huge underground gold, platinum and coal mines. Working methods were mature, but there was burgeoning pressure to increase productivity, whether by harnessing the ability to drill large diameter holes or by increasing the yield per blast from limited face length.

Explosives technologies were also developing and offered great promise for moving toward these goals.

The marketing group of the Explosives Division, under the General Manager Peter Lambooy, ran a team of explosives service engineers, mainly drawn from the mining industry, which worked with the company and its customers to implement efficient and safe blasting both in the country and in Africa. The demand for help in applying the new technologies and implementing safe and efficient blasting was more than the service engineers could handle; the result was “Explosives Today”, a technical bulletin written by these engineers, which would become a globally recognized source of useful blasting information.

The first issue, “ANBA and Inclined Drilling”, was published in August 1965. Series Two started in September 1976 with “Selection of Explosives for Narrow Reef Blasting”, and finished with “Safety in Surface Blasting” in 1988. The first issue of the third series, launched in September 1988, was “The Historical Development of Commercial Explosives”, and the series ended with the tenth issue, “Destruction of Explosives Accessories” in December 1990.

The series was such an acclaimed resource for blasting information because it was entirely written by the engineers engaged in real blasting activities, subjected to intense peer review, with the meticulous attention of senior engineers. For most of this time, AECI Explosives (which changed its name progressively) was either the only explosives supplier, or by far the majority supplier, and had not yet encountered the disciplines and pressures of working in a highly competitive market.

Long after the series was discontinued, old copies have been treasured and used as vital reference by personnel concerned with safe and efficient blasting around the world.

And now...

In line with our value proposition of Thought Leadership and a move to revive the publication, AEL’s Mining Optimisation Team has replaced these treasured copies with a new series. The first two issues were produced in the first quarter.

This technically driven customer publication authored and tailored by our Mining Optimisation team is now available to customers in the form of an A4 folder equipped with a CD and flash stick containing all issues of the publication.

For more information and to order your copy, contact the Mining Optimisation Team c/o Simon Tose,

Tel: +27 11 606 3960

Email: simon.tose@aelms.com

Explosives TodaySeries 4 I No 10

Stope timing with ShocktubeHenk Esterhuizen – Senior Mining Engineer

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1. Overburdened blastholes

The majority of the gold and platinum ores occur in the narrow, hard rock reefs. Stoping methods usually require the drilling of 0.9 to 1.5m blastholes at 70° to 90° to the face, with burdens in the region of 0.6 to 0.9m.

Under these difficult breaking conditions, any overburdening of the blastholes can result in the following problems:

• Reduced face advance• Damage to support and scatter barricades from blown

out shots• Increased slabbing off of the face and hanging wall

ahead of the exploding shots, resulting in cut shock tube

• Creation of a bad hanging wall condition which is exaggerated the longer the overburdened hole

• A bump on the face which prevents effective face cleaning by the scraper and which increases the chance of cut shock tube

• Cutting off of the next hole where bottom priming is not practiced

As a result of these problems and in trying to avoid them, the use of less than optimum burdens compromises drilling and explosives efficiencies.

The following are the normal causes of overburdening and should each be considered when attempting to improve matters, figures 1&2:

• Holes drilled off-line or collared incorrectly• Missing or short holes• Under gauge or undercharged holes• Misfires• Out of sequence firing

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The out-of-sequence firing problem can to a large intend be avoided by the correct use of the Uni-delay Shock Tube, the initiating system normally chosen for reef stoping owing to its safe ease of use, flexibility and general reliability.

2. Principle of connecting shocktube

The basic principle of connecting with Shocktube assemblies is as follows, figure 3:

• The incoming signal through the tube of the first unit will initiate both the out-hole and in-hole detonators of the next unit

Explosives Today - Series 4, No 10

Figure 1: Identifying problems in the face - Drilling

Figure 2: Identifying problems in the face - Drilling

• These detonators will then fire at their respective delay times

• The process repeats itself until all the holes are fired

3. Burning Front

Uni-Delay LP assemblies, which have an out-hole delay of 200 milliseconds and an in-hole delay of 4000 milliseconds, will mean that 20 sets of holes (double connection) will be initiated before the first hole fires, figure 4.

4. Benefits and features of shocktube

Benefits• All in-hole detonators have the

same delay• Rugged, abrasion-resistant tubing• Easy to connect• Easy to check connection

sequence when “walking the blast”

• Ergonomically designed connector block makes connection of tubing easy

• Workplace friendly (unleaded)

Features• 20 hole burning front• Transient connector body• 18 kg minimum break load• Immune to hazards of radio

frequency radiation, stray currents and electro-static discharge

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Owing to the many factors involved, it is strongly recommended that optimisation of stope blasting is discussed with AEL Mining Services’ Explosives Engineers.

5. Recommendation when using Shocktube assemblies

5.1 Safety1. Handle with care - all detonators

are explosive2. Temperatures of ›90°C may result

in spontaneous explosion 3. Severe impact on the detonator

or tubing can result in accidental initiation and explosion

4. The in-hole detonator is an 8 strength detonator and the out-hole detonator is a 2 strength detonator

5. The Shocktube can be initiated by a minimum 2 strength detonator

Explosives Today - Series 4, No 10

Figure 3: Principle of operating the Shock Tube system

Figure 4: Illustration of the “Burning Front”

5.2 Length of shocktube protruding from a hole

The length of shocktube protruding from a hole will solely depend on the hole length and burden, if for example: a 1.2m hole is drilled and where a 0.60m burden is used then it will be viable to use a 2m length Shock Tube. This will leave 0.80m Shock Tube protruding from the hole which will be sufficient to connect to the next hole.

5.3 Position of detonator in hole Stope blasthole depths vary from

mine to mine. In order to achieve the required length of shocktube protruding from a hole, it may be necessary to vary the position of the primer. To prevent cut-offs it should be retained in the bottom third of the hole. Reverse priming is not recommended due to the

following:• Damage to the shocktube• Increased risk of accidental

detonation due to being struck by the loading lance or charging stick

• In the case of a misfire, the detonator may become wedged across the hole, thus increasing the risk of accidental detonation in attempts to remove the detonator

6. Timing – Methods of connecting shocktube

6.1 Narrow stoping width upto 1.5m

The risk of misfires, which might occur due to falling rocks which might cut the shock tube, is decreased when doing double connections.

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Explosives Today - Series 4, No 10

The disadvantage of this timing method is the fact that the top hole breaking angle is decreased resulting in potentially more damage to the hanging and therefore increasing the probability of falls of ground.

Normal timing method (single connection) is not recommended due to the increased risk of misfires caused by cut offs.

Figure 5: Normal Timing – Staggered Pattern (Double Connection)

Figure 6: Normal Timing – Staggered Pattern (Single Connection)

Figure 7: Reverse Timing – Staggered Pattern

The reverse timing method is highly recommended when stoping widths and hanging wall conditions need to be controlled. Top hole breaking angles are reduced which creates easier breaking and therefore damage to the hanging wall is reduced. Drilling discipline must be maintained to ensure proper blasting associated with this timing method.

When drilling block/square pattern this method will result in a more consistent burning front with sequential firing achieved; which will improve the throw of rock and advance per blast with finer fragmentation.

Increased breaking angle; therefore damage to the hanging wall is reduced when using this method. Undercutting and

Figure 8: Normal Timing – Block/Square Pattern (Double Connection)

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Explosives Today - Series 4, No 10

hanging wall control should more easily be achieved.

6.2 Wide stoping widths (+1,5m)

There are a number of acceptable methods for these conditions. The method (Multiple Rows of Blast holes) shown has the merit of simplicity and economy as well as minimizing the chance of misfires.

Figure 9: Reverse Timing – Block/Square Pattern

Figure 10: Multiple Rows of Blast holes

7. Conclusion

There are many ways of connecting shocktube; the best method is the one which achieves total initiation of all blast holes with the greatest certainty. Combined with correct charging practices, in each specific situation, correct timing will ensure the best possible results.

AEL Mining Services’ Explosive Engineers based at the regional offices are available to help and advise on the use of shocktube for all blasting scenarios.

This document replaces all previous Explosives Today on this subject including:

• Series 2. No 28: June 1982 Stope

timing with fuse and ignite cord, PJ Potter

• Series 2. No 39: September 1985 Nonel systems in underground blasting, NE Bird

• Series 3. No 6: December 1989 Nonel reefmaster in narrow reef stoping, C Hughes & KS Ireland

AEL Mining Services Limited (PTY) Ltd1 Platinum Drive, Longmeadow Business Estate NorthModderfontein, 1645Tel: +27 11 606 0000www.aelminingservices.com

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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.

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