The use of high-speed video for the research, development and monitoring of the performance of blasting procedures is a well-proven but under utilised practice
The practice of recording blasts for quality control purposes has been conducted for several decades. However, at the low frame rates of a standard video camera, essential data is frequently missed as it occurs when the shutter is closed between frames.
The recent development of low-cost, easy-to-use high-speed digital cameras and user-friendly software can deliver a capability into mine management as a day-to-day production tool that can greatly improve blasting performance and reduce costs.
Digital high-speed video and image analysis software can accurately quantify each blast. Analysis of the images can facilitate the identification of causes of variance from design, geology changes, errors in blast practice and areas of poor performance. The use of high-speed video greatly enhances the audit and review processes so that future blast design can be quickly and appropriately modified to deliver improved blasting performance and reduced costs.
Capturing images at 1000 frames per second (fps) allows analysis on a millisecond timescale, where detonator timings, fragmentation, venting, fume generation and flyrock can be accurately identified.
The mining industry in 2015 is facing challenges brought on by low commodity prices, a weak worldwide economic climate and vocal public/community scrutiny. To prosper in this environment, the industry needs to do more than maintain the status quo. Continuing to do what we have always done, even creating improved efficiencies, may not yield the gains that will promote prosperity.
What is required is a paradigm shift in the ways in which we operate. What we face is the law of diminishing returns, and doing things differently and smarter provides the opportunity to remain sustainable. Designing blasting purely by rules of thumb discounts the dynamic conditions of a blast. The design protocol must proceed lockstep with reliable analysis and immediate review. Analysing the result and the downstream effects is only half of the analysis that can be undertaken to providing that review. Analysing the blasting process provides detailed information to enable review of the process to achieve a better result.
Current blast analysis is often conducted based upon measurement of the design and the end resulting muck pile.
The missing components can be the analysis of the rock mass being blasted and the dynamic process happening in real time within the blast itself. This is best achieved by playing detailed visual information to both the blast design engineers and the drill and blast team immediately after the blast event and before they depart the mine site. At this point, every action taken by the drill and blast team is still fresh in their minds. The best analysis tool is in the grey matter residing between the ears of the team. No computer can compete with this accumulated body of knowledge.
Control of all aspects of the blast process with a viable visual record provides impartial evidence that can demonstrate the due diligence afforded to the blast design and compliance with the conditions of the licence to operate.
The operating environment
Public concern, technology advances and immediate proliferation of information, including social media, are creating a strain on the relationship between industries that are perceived to threaten the environment and the population that they support.
The mining industry is aware of this operating environment and has an awareness of all stakeholders to remove the reason for public distrust. Many organisations have taken steps, some major, towards achieving a sustainable future that is not at odds with the environment or their neighbours. Transparency in all facets of mining operations is needed to restore public confidence. To grow public confidence, the mining industry needs to demonstrate good corporate citizenship. Political confidence rests upon the economic benefits provided by the mining industry; however, political favour is driven largely by public opinion, and the driver of public opinion is the communities in which the mines operate.
Advances in technology are delivering measurable improvements in productivity, environmental outcomes and monetary efficiencies to many manufacturing and food processing industries. These same technologies can assist with improved mining processes and provide factual information that can be used to assist in gaining a successful outcome for all.
Uses of images and vision
Vision is our most basic form of communication; seeing is believing. We immediately interpret vision and evaluate the visual content according to our particular requirements. If we can see it we can make judgements and evaluate the information contained within the visuals (Crump, 1991).
Until quite recently, the use of high-speed imaging technologies was confined to large companies, government departments or university research groups. The high cost involved, the complexity of the equipment and its operating procedures, and the day-to-day operating costs of such equipment proved too much for small- or medium-sized organisations.
However, the rapid improvement in conventional video cameras, digital high-speed video cameras and user-friendly image analysis software has changed all of that.
Today, any company in the extractive industry – small, medium or large – can afford to operate quite advanced high-speed digital imaging systems and image analysis software as an integrated part of its operations. The cost benefits of such procedures are so well established that to not use such systems can place an operation at a distinct disadvantage to its competitors (Giltner and Worsey, 1986). In addition, the increased accountability that extractive industries are facing demands irrefutable proof that good management and environmental procedures are being followed. The application of modern digital imagery
and software can:
- monitor and analyse blasting performance
- help assess crusher performance
- aid dragline, shovel and/or loader performance monitoring
- assess conveyor belt damage analysis while the belt is in use
- record accident impact monitoring on driverless mine vehicles
- record track and wheel condition on moving ore trains
- monitor the cowcatcher impact of driverless ore trains.
Types of video systems available
Domestic digital video
Until recently, this has been the most cost-effective method of achieving realistic images for archiving blasting activities, crushing and conveyor images. The big advantage of this system was the immediate replay facility allowing the visual analysis of data whilst the event was still clear in the minds of the operators, thereby maximising the evaluative capabilities of experienced staff.
Domestic digital slow-motion cameras
The emergence of domestic digital slow-motion cameras that can record in HD to about 150 fps has revolutionised the analysis capabilities available because of the higher frame rates these cameras can achieve. They have one major drawback: image compression. All domestic digital cameras compress the image file to allow the fast transfer of images to the recording medium.
Low-end digital high-speed video
This is the area of rapid expansion in both the type and quality of the equipment available. High-speed digital video equipment allows the capture of the dynamics of a fast event where the detail of the event – such as blast detonation timing, fragmentation, misfiring, geology changes and blast breakthrough – are sampled and recorded. The event can be viewed or replayed at a speed whereby the human eye can detect all or most of the dynamic action captured. This provides the information necessary for an experienced engineer or technician to evaluate what happened.
This procedure is extremely valuable when you are trying to analyse blasts, conveyor belt systems, crushing processes, drilling or any mechanical or dynamic processes that happen faster than the human eye can follow. Once captured, the images can then be downloaded to a computer for replay, analysis and archival purposes.
High-end digital high-speed video
High-speed camera images have always been considered the ‘gold standard’ when conducting image analysis of blasting and other high-speed processes. The quality of the images is high, and the ability to analyse single images and then compare sequential images has made this an invaluable tool for those who could afford the high costs involved. The high quality of digital high-speed imaging systems were usually too expensive, for example, $60 000-120 000 for a turnkey system. Whilst delivering high-quality images, such systems required trained technicians to operate them.
However, new generation digital high-speed camera systems now commence at $27 500 for a complete system, with the high-end systems costing $120 000-260 000. Table 1 compares the various levels of equipment available.
Common blasting concerns
Competing factors control blasting practices. Explosives manufacturers would prefer to sell the maximum use of explosives for a blast, mine managers would prefer to buy the least amount of explosives to keep costs as low as possible, while mill operators would like a steady and uniform feed size to maximise throughput. In addition, environmental and community concerns need to be correctly addressed and monitored. Finding the balance between too much and not enough keeps blasting consultants and others in business.
Harrington (2005) said: ‘measurement is the first step that leads to control and eventually to improvement. If you can’t measure something, you can’t understand it. If you can’t understand it, you can’t control it. If you can’t control it, you can’t improve it.’
The purpose of mining is to recover resources that the community needs cost effectively, and blasts are designed to contribute to this by fragmenting rock either for removal or to release the mineral from waste rock. Design rules can be simple or can use rock mass ratings and other parameters to maximise recovery and fragmentation.
Measurement is usually based around muck pile shape, dig times, overburden removal, mill throughput and the requirement for secondary breakage. Blast designs are altered to improve these parameters. What are not measured in this process are the sources of poor compliance or variance between desired outcome and broken rock on the ground. High-speed video can measure parameters as the fragmentation happens. Using a high frame rate, and provided that the camera is placed strategically so that the critical parts of the blasting process are visible, the video can capture:
- variances in detonator timing
- sources and location of variable fragmentation
- stemming ejection/rifling
- sources of NOX/fume creation
- sources of flyrock
- breakthrough into orebody/coal seam
- face bursts.
Higher resolution images and faster frame rates
Table 2 lists the speeds at which common blasting events happen and suggests some minimum frame rates that could be used to capture detailed information.
There are three interlinked parameters that limit the ability of any digital photographic method. These are shutter speed, aperture and sensitivity of the image chip. The shutter speed can theoretically be as slow as the inverse of the frame rate, eg 1000 fps shutter speed has to be faster or equal to 1/1000 sec. Faster shutter speeds means that the chip receives light in whatever fraction of a second the shutter is open, and either the aperture needs to be opened to allow more light in at the cost of depth of field or the chip sensitivity needs to be increased to react to lower light levels.
Improvements in chip technology have allowed for more sensitive chips. This means that we can capture events with fast shutter speeds and reasonable apertures to maintain depth of field.
Figure 1 is a still from a modern high-resolution camera with a frame rate of 1000 fps. At this rate, signal tube lengths at around 2 m are illuminated. At this frame rate, each signal tube will be captured in a frame and each detonation will also be displayed. This allows auditing of the design for implementation compliance and enables troubleshooting of design flaws as they will be seen in the playback of the video.
Visible in Figure 1 are the signal tubes burning, in each case the length of burn is less than the spacing between holes. A considerable amount of energy is directed upward, and the resultant local flyrock is visible.
The use of any visible light technology is limited by the available light. Newer sensors have improved sensitivity so that this is becoming less of an issue. The presence of dust between the camera and the subject of interest can obscure vision; however, appropriate camera placement and mine site dust management procedures will mitigate this. Most of the data collection that may need to be analysed, eg detonator timings, will be captured before generated dust obscures the field of vision. Also, the use of multiple cameras when necessary can alleviate the loss of vision in this event.
As previously discussed, standard video is limited by frame rate; however, ground vibration has a more significant effect on the quality of images collected. By contrast, high-speed cameras have two features that effectively negate ground vibration interference with image quality. These are the frame rate and the high shutter speeds that they offer. The combination of these two parameters means that the camera movement is so slight when the shutter is opened and closed that it is insignificant in its effect on image quality. The arrival of the ground vibration waves will be captured by the camera movement as the centre of the image will change with the movement of the camera and tripod. This can be seen on playback and may be of assistance in ground vibration analysis.
Lack of training of camera operators can reduce this technology to a dust-collecting shelf item. A rudimentary knowledge of photographic techniques needs to be developed to ensure that the camera is set up in the most appropriate available location. In conjunction with this, a working knowledge of the blasting process is required to ensure that the operator can capture the correct subjects of interest. To obtain maximum benefit from the captured images, it is desirable that the initial analysis and communication with the blast crew happens before the crew signs off and leaves the site by reviewing the footage with the drill and blast crew immediately after the event. Important information related to blast performance can be documented whilst it is still fresh.
Current contracts for blasting services in the larger mines have changed from the supply of explosives to a total package where the amount of ore or overburden delivered has been the primary contract condition (rock on ground). These contracts usually specify fragmentation or particle size percentages and rock or orebody movement. How can a mine monitor the contractor’s performance against these criteria?
Visual technologies such as conventional and high-speed digital video provide economical, easy-to-use, irrefutable information about performance. This technology can and is used extensively by service engineers and technicians to monitor and maintain mechanical processes such as assembly lines, packaging, crushing, conveyors, etc where the process is too fast for the human eye.
If this technology saves one breakdown it usually has fully paid for itself. Bottling and packaging plants routinely report improvement factors of five to 20 per cent when this technology is installed and regularly used as a maintenance diagnostic tool. By utilising this in blasting, refining blast designs, auditing designs and evaluating good footage, a mine may reduce the explosives consumed and achieve a better result simply by being able to measure and thus control more aspects of the blast process.
The value of recording all of the blasting and regular segments of other processes at a mine will quickly support any argument that the mine practices good governance of community responsibilities.
If an environmental problem exists, visually recording current practices and then visually recording the improvements provides powerful evidence that the improvements made demonstrate due diligence. This helps to remind legislators and courts of the success of the program that the mine implements. It is essential that there is an impartial witness, that is, unedited footage of all that transpired. Being in control of the visual images
used in an environmental argument provides the best way to allay fears
within the community.
The integrated use of visual information in mining is not new (Brown, 1995). Utilising the information gained from observations is how the world is interpreted and how appropriate responses are made. What is new is the ability to slow down fast processes to the point where it is possible to absorb the information contained therein. The major benefit from this is that measurements can be taken and creative and lateral thinking can be applied to improve the process (Banks, 1990).
This is an extract from a paper published in the proceedings of FRAGBLAST11, held in Sydney from 24-26 August. Members can download the full paper at the AusIMM website.
Banks S, 1990. Signal Processing, Image Processing and Pattern Recognition (Prentice Hall).
Brown J, 1995. Drilling and blasting impact on dragline performance, in Proceedings ExpIo 95, pp 341–343 (The Australasian Institute of Mining
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Crump F, 1991. The application of S-VHS camera and VCR equipment with editing capabilities to the analysis of commercial blasting operations, in Proceedings The Society of Explosives Engineers Conference, pp 191–196 (The Society of Explosives Engineers: Cleveland).
Giltner S and Worsey P, 1986. Blast monitoring using high speed video research equipment, in Proceedings The Society of Explosives Engineers Conference, pp 173–191 (The Society of Explosives Engineers: Cleveland).
Harrington H J, 2005. Process Management Excellence: The Art of Excelling in Process Management (Five Pillars of Organizational Excellence) (Paton Press).