10. Simon St John a Practical Approach to Managing Control of Flyrock

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A Practical Approach to Managing Control of FlyrockSimon St John Tose

PrEng, BSc (Hons), IOQSA, SAIMMGroup Consulting Mining EngineerAEL Mining Services, South Africa

AbstractWe have had a long history in supporting the development of training material to ensure safe blasting.This has been provided as both significant technical guidance to the industry and input into the

development of the new industry surface rockbreakers or shotfirers qualification in South Africa (RSA).

The learning material supplied to the industry is based on both a classroom knowledge component and

an assessment on the practical application of the learning by the trainee blaster on the job under thesupervision of the appointed blaster. This training includes all blasting applications which can often

extend beyond the normal mining environment of open pits, underground and quarries into civil

applications such as trenches, blasting close to private buildings, public roads, pipelines, power lines,

swimming pools and the removal of concrete structures and building demolitions etc.

A number of recent flyrock incidents prompted us to review the learning material and look at an

improved means to help educate and support the incumbent and new blaster. The intention was to beable to provide a simple tool for the blaster to verify that all is done and checked in terms of best

industry practise.

We also noted from our analysis that the primary key to the control of flyrock was:

The correct attitudebeing adopted by the mining operation and in particular the appointed blaster and

not a set of tables or equations

This paper shares the matrix that was developed from on bench observation and makes use of a

number of industry investigations, video examples and analysis to illustrate how is was structured, can

be used to address and check the key issues that need to be managed by the blaster.

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Copyright 2013 International Society of Explosives Engineers

2013G - A Practical Approach to Managing Control of Flyrock


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Introduction"Flyrock" means rock that is thrown through the air as a result of blasting. Flyrock is an integral part of

blasting that needs to be properly controlled. If flyrock is uncontrolled the rocks, which can travel

significant distances, pose a serious risk to persons involved with blasting as well as anyone else and

equipment located in the area of the blast. The encroachment of human habitation around the mine sitesas the result of the search for work and offering supporting industries to the mining operation has

intensified the need to manage flyrockand blast risk zones.

During the past couple of years several mining sites in South Africa, RSA reported that property damage

had occurred after blasting as the result of flyrock, fortunately no injuries to people had occurred. One of

the industry bodies, the Institute of Quarrying, Southern Africa, IOQSA, asked us to assist in revising

the learning material used as part of the professional development of existing blasters and the training ofnew blasters. Rather than just a checklist they were looking for a one or twopage matrix to help guide

the blasters to understand the various controls needed for the management of flyrock for safe blasting

on said mining or civil blasting sites but also the relationshipsbetween these controls.

The intention of this document is to share the positive learning in an open industry forum and it must be

emphasised that all involved had followed the Best Industry Practises at the time of the incidents. It is

also a need to be able to share without prejudice and evolve these Best Industry Practises to avoid andreduce the risk of any potential events for the Industry in the future.

ActionAn investigation process was implemented which included site visits and analysis of the drilling plans,

blast designs, blast and explosive loading reports, timing plans and interviews with site personnel. A

literary review of international papers, articles and incidents along with the best practise of filming all

blasts enabled us to review frame by frame and confidently support the determination of the root causesof the flyrock incidents.

Result

As part of the review and revision of the learning material a matrix , figure 1, was developed toprovide a summary for the blasters to use in their day to day activities. Four key areas were identified

during the investigations which could be split under Natural anomaly and Human influence:

Natural anomalyo Understanding location/terrain

Human influenceo Operational issues

Mine site On bench

o Supervisiono Blasting parameters

The Natural anomaly was the understanding of the rock properties and geology and the impact on

blasting. In addition there was a need for the blaster to better understand the impact of environmentaleffects such as cloud cover, wind and atmospheric effects.

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On the Human influence were the operational issues, those under the direct control of the blaster, onbench such as charging, stemming and connecting of the initiation systems (Timing). The mine site

factors involved the determination and closing of the blast risk zone at blasting time.

The supervision leg is often completed by other team members such as drilling and bench preparation,before being signed and accepted by the blaster.

Lastly was the blast design itself and the many parameters that make orbreak a good blast design.

Figure 1. The Flyrock matrix

DiscussionTo understand this matrix we need to illustrate this from the number of incidents used in itsdevelopment. The first flyrock incident was the lack of proper understanding of the impact of geological

slips on the blast design.

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Figure 2. Not considering geological features in the blast design

As we can see, figure 2, whilst the blast design followed sound principles, with an appropriate powder

factor, the use of a larger hole diameter resulted in the burden and spacing falling outside the

predominate geological planes. This was not identified in the application of the blast design on the benchresulting in poor fragmentation but of greater concern flyrock, figure 3. The blaster however correctly

mitigated the risk blast area secure to avoid any potential damage or incidents.

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Figure 3. Blast design not accounting for the geologic structures

At another site the lack of control of the bench preparation and understanding by the team preparing the

bench for drilling and blasting led to another incident, involving damage to several structures and motor

vehicles, figure 4. The findings of the investigation, in part, revealed the need for clear proceduresbetween the different work teams, a sign off and acceptance that the bench had been adequately prepared

drilling and later blasting. In other words all loose and broken material and potential missiles had been

removed. This is highlighted in the link in the matrixbetween Operational issues and Supervision.

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Figure 4. Bench preparation

The final incident brings together the matrix as it was established during a site visit that the damage

had resulted from possible flyrock originating from two areas of the blast. A portion to the rear of the

blast and from secondary blasting removing a pinnacle situated in front of the blast block, figure 5.

The evaluation was based on the site visit and analysis of the Drill Plan, Blast Design/Blast & Explosive

Loading Reports and Timing Plan. The post blast data includes an analysis of a blast video and

interviews held with site personnel.

The bench was reported as waterlogged with significant geological features and loose material on the

surface. Approximately 60 holes had previously been drilled at a hole diameter of 165mm (61/2)whilst

the remainder of the block had been drilled on the same blast parameters at 140mm (51/2). A significant

number of holes had not been drilled/or had collapsed as a result of the geology. The reports indicate

that the charging and stemming process was normal, although it is noted that 16 holes were topped up in

the area of the larger hole diameter.

The timing pattern used was a box cut design, initiated from row 19, with 30ms between rows and an

8ms stagger to the right of row 19 and 25ms between holes.

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Figure 5. Lost/Missing/Failed holes reported during Drilling and charging operationsas a result of geological conditions

The investigation and a video have revealed that the contributing factors to the incident are:

Geological conditions

Bench preparation

Holes not drilled, missing or collapsedo Overburdened holes would have contributed to creating potential flyrock

Two hole diameters: 165mm & 140mmo Change in diameter adds approximately 6.6 kg/m of explosive mass per meter of column

Approximate powder factor increase of +/-39% in the area of the 165mm diameter holeso Explosive top up could add to this, as it is possible that explosives had been lost due to

geological conditions

Secondary blastingo Surface Detonating cord used for timingo Short, angled and different length drilled holeso

Control of stemming lengths resulting in unconfined explosives

Using the matrix, figure 6, we could determine that the following should have been considered in the

design and implementation of this blast:

1. Review procedures on bench preparation

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2. Poor geological conditions identified during drilling/charging and the missing/blocked holes mayresult in the need for increased stemming heights

3. Best practise would require that for a given blast block the hole diameters are kept constant withan appropriate blast and timing design

4. Secondary breakinga. A timing pattern should be used to attempt single hole firingb. The roles, responsibilities and sign off on the blast design and timing need to be reviewed

as two different explosive companies were involved.5. In this situation the blasts should have been handled separately

a. Review risk and safety areas on secondary blasting due to the nature of thestressed/broken/blast damaged material involved

6. Control of the explosive mass and stemming is critical

Figure 6. Blast design

The matrix is being developed with supporting material to enhance the development and training ofboth existing and future blasters to promote safe blasting, comment is more than welcome.

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ReferencesSafety Evaluation of Blasting Flyrock Risk with FTA Method, ZHOU Zilong, LI Xibing, LIU Xiling &

WAN Guoxiang (School of Resources and Safety Engineering, Central South University, Changsha

410083, Hunan, China)

Various Government/Industry Hazard/Accident notificationsSiskind DE, Kopp JW (1995). Blasting accidents in mines: a 16-year summary. In: Proceedings of the

21stAnnual Conference on Explosives and Blasting Technique. Cleveland, OH: International Society of

Explosives Engineers, ISEE, pp. 224-239.Various papers by Alan B Richards and Adrian J Moore, including Flyrock control by Chance or design,

ISEE New Orleans 2002

Little, T N, 1994. Practical approaches to airblast monitoring and management, in Proceedings Open Pit

Blasting Workshop (OPBW94), Perth, pp 144-155.Lundborg, N, 1981. The probability of flyrock, SveDeFo report, DS.

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10. Simon St John a Practical Approach to Managing Control of Flyrock

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