Fog management – an ever-evolving balance between science of behaviour and tech

By Sharyn Macnamara

Sharyn Macnamara met with Rock Engineers at Sibanye-Stillwater’s Khuseleka shaft, Rustenburg operation, to discuss some of the latest innovation and technology developments in safety procedures in Fall of Ground (FOG) management in the South African mining PGM sector. The discussion focused mainly on the delicate balance that must be achieved between the management of the rockmass, the interaction of people with such rockmass, as well as the evolution of processes and technology to mitigate risks in the ever-changing underground mining environment.

Shane Durapraj, manager Rock Engineering at Sibanye- Stillwater SA PGM, Clarence Mutsvanga, unit manager Rock Engineering at Sibanye-Stillwater and Neo Ndlovu, Senior Rock Engineer form part of the team of Rock Engineering professionals that assist with managing and mitigating the risks of FOG at Khuseleka shaft – a vertical shaft system within the Sibanye-Stillwater PGM Rustenburg operations, that utilises conventional mining methods to extract the valuable ore.

The conversation starts with an intrinsic element of legislation. Durapraj makes the point that, “As a collective, the mining industry, of which Sibanye-Stillwater SA PGM operations plays a pivotal role, is bound by regulations contained in the Mine Health and Safety Act (MHSA). Amongst other aspects, we must ensure the stability of the rockmass by using a FOG management system that caters to the rock characteristics and conditions that are prevalent at each operation, and then design support systems, processes and procedures that promote stability. Apart from empirical design methodology, we use the Minerals Council South Africa’s leading practices – for example, the ‘entry examination and making safe’, ‘netting and bolting’, ‘ledging’ and now more recently, ‘workplace illumination’ – to aid the entry examination process, over and above the other personal protective equipment (PPE) which includes individual cap-lamp lighting. These are all, among others, processes and procedures that feed into the support system – to help mitigate the risks at the face and to assist in the prevention of injuries and fatalities at our operations.”

The team agrees that there is no single procedure or technology that is ‘a silver bullet’ when it comes to FOGs. Apart from managing gravity-induced FOGs, rock engineering is about attempting to manage and limit the impact of seismicity in the PGM environment . The reality is that, after every blast, the work environment is altered, so the challenges that were dealt with yesterday, may not be the challenges that are faced today. And this is where the human factor plays an important role in the safety equation. The company has, therefore, embarked on a number of intervention programmes to support and promote internal company safety procedures, processes and leading practices so that a safety culture is embedded. How the workforce responds to hazards and challenges in the work environment, minute by minute, is of utmost importance to both the organisation and the workers who MUST return home safely each day. Sibanye-Stillwater ensures that each worker is appropriately trained and found competent for the tasks that he or she needs to accomplish each day.

Trigger Action Response Plans (TARP) and innovative visual aids Earlier, the team mentioned that after each blast, the rockmass presents differently; where new geological features are exposed, and new hazards arise. Khuseleka follows the industry-accepted leading practice called the Trigger Action Response Plan (TARP) hazard identification programme¹. Each team is trained and equipped with a series of standards and strict protocols to manage and mitigate these hazards. During the Entry Examination and Making Safe (EEMS) process, a visual inspection is conducted at the workplaces, hazards are identified through TARP and the appropriate team treats the hazards by installing the pertinent support units before mining activities may commence.

To expand on the procedure, Ndlovu explains, “While making safe, our crews are empowered to identify geological features and hazards in entry examination first and know who to escalate the problem to, based on the TARP 1, 2 or 3 criteria.”The next step is to assess and install the required support to mitigate the hazards identified. This may take on the form of mechanical props, nets, mesh, additional support, elongates and roof bolts, among other solutions. This happens during each shift, every day. To promote the visual identification of the TARP triggers, the Khuseleka Rock Engineering team have implemented two innovative visual aids. The first is a visual marker/cue that was initiated to protect the crew on entry examination – the Lekoba stick – named in honour of a colleague, Mr Lekoba, who passed away in 2013 after a FOG incident during the EEMS process. This stick/cue is suspended from the roof or hanging wall and demarcates the area that has the last line of support, has been inspected – and up to that point – is declared safe for work. The team MUST NOT proceed past these reference points. The brightly coloured stick, often lit, acts as both a symbolic reminder that the area past this point has not been inspected and therefore may not be safe, as well as serving as a practical tool, which underground teams respect and adhere to.

Taking TARP a step further, Ndlovu, in collaboration with an industry expert, Norman Rangwetsi , developed the TARP ruler. These innovators adapted a measuring unit that is used by the teams regularly underground, to suit the identification method in the TARP process. Ndlovu has been working on this engineered tool for a while now, perfecting the components, so that the teams have another visual method of identifying a hazard. The tool is calibrated and colour coded to mimic heights of potential roof failure (brow heights) and also has an angle measuring feature. Each colour represents a different brow height, and the angle of a geological feature can be measured using the angle function. It is a simple tool that the teams can use to accurately determine what the TARP rating should be and thereafter, what the mitigation should be. (See video https://youtu.be/IwMjxM2jly0)

Ndlovu explains the various colours (red, orange, green) and mitigation: When a brow height is measured and the height only extends to the green part of the ruler, it is classified as a TARP1 (25-50cm), which is typical of a small brow or a rock that is dislodged along a rock joint. These minor risks can be dealt with by the entry examination team themselves, who will rectify as per the mine standard and thereafter, continue with normal mining activities.

An orange section of the ruler represents a TARP 2 condition, where the brow height is of the order of 50-75cm. This is a more hazardous rock condition and requires the team to stop, barricade off the area and escalate the problem to the appropriate team within the mine’s specialist structure. The TARP2-trigger will require action from a production supervisor or shift boss, mine overseer, health and safety representatives, and/or safety officer. This does not mean that a rock engineer and/or mine manager cannot respond to the call. This team will inspect the area and give specific instructions to the crew on how to mitigate the hazard.

The top section of the ruler, measuring the greatest brow size (0.75m-1m ), is colour-coded red as it is high risk (TARP3). The team called in in this instance is a senior team, comprising rock engineers, mine overseers and mine managers, as well as the TARP2 team. Again, the mining crew will carry out the instructions requested by the TARP3 team. The last aspect of the ruler talks to the angular measurement of a geological feature. Rock engineers are aware that when geological features are flatter, namely less than 600, there is a high probability that it may result in a FOG. On the ruler, the red angle measures such a feature and the team can quickly determine how to mitigate the hazard using the TARP process, as well as using the appropriate tools or support to mitigate the hazard.

“The entry examination teams – often from the older, more experienced generation of miners – have reacted well to this new tool. It assists them in measuring features using practical visual colour cues, with the additional mechanism to help measure angles of the brow, which is sometimes difficult to judge, but very relevant in the decision-making process at the workplace faces, as well as other underground areas of the mine. The angle measure assists them in identifying the more hazardous angles,” says Ndlovu.

Daniel Van Nieuwenhuizen, a senior shift supervisor in section 262, was the first person to use the re-adapted and re-engineered TARP ruler underground. He notes, “The TARP ruler is a safe, practical system that empowers all supervisor level and general employees. It gives employees the confidence to identify hazards and take corrective action to make the workplace safe. The miners and team supervisors, when making use of the colours on the ruler can safely identify, classify and know which team to call or action to take based on the TARP procedure. We believe that we can make a difference with this system and save lives by preventing falls of ground.”

Daniel Van Nieuwenhuizen, senior shift supervisor in section 262 Khuseleka mine. Image supplied by Sibanye-Stillwater

Key to the TARP process, and the tools that are used during this process, is that only once the remedial or mitigating action has been completed, the conditions to proceed have been met and all role players have signed off, may normal mining activities commence. Depending on the mitigation, the work area may be stopped for any number of hours, days or weeks. In some cases, where it is too hazardous to mine, the workplaces could be stopped permanently, and the crews moved out.

Evolution in ‘Netting and Bolting’

The discussion to this point concentrated mainly on the TARP identification process within the EEMS procedure. In parallel to these processes, the Sibanye-Stillwater rock engineering discipline also designs procedures and standards that mitigate against failure of the hanging wall during the support installation and drilling phase of the mining cycle. To ensure that the persons installing support and drilling at the face have sufficient areal coverage under which to work, the mine employs pattern bolting and temporary or permanent netting. Ndlovu says, “Over the past two to three years, the Sibanye-Stillwater underground operation has redesigned its support system to cater for fall-out loads up to 2 tonnes. In addition, the temporary support units have been re-engineered to carry similar loads. This has enhanced the protection of workers and improved the risk mitigation strategies of the organisation in its quest to achieve a Zero-Harm culture.”

Durapraj agrees with Ndlovu and adds that there has been an evolution in the number of support types and products –‘the toolbox’ – available to the shaft rock engineers to mitigate hazards. He explains that “The rock engineer on the shaft now has more tools that he can use to apply an exacting solution to the problem for each ground condition presented. To aid the shaft rock engineer, the mine’s code of practice provides guidance and mitigation strategies for particular ground control districts (GCDs).” Mutsvanga weighs in, noting that if a design change is made at an operational level, it would only move to a solution that offers greater strength, support and risk mitigation than what was prescribed before, and this would require sign off at the highest level.

A further advancement in the toolbox is that of permanent nets, that is, where the nets are not removed before the blast. Durapraj points out that, “There is a move towards permanent areal support, which means that every square centimetre of a hanging wall will eventually be covered by some form of support – whether it is wire-mesh, a net, a TSI or a fabric spray.” He explains that historically in the PGM sector in South Africa within the Bushveld complex – from Rustenburg all the way over to Limpopo and Mpumalanga – the uptake on permanent areal mesh has not been as prolific as it has been in the gold sector. However, as platinum mining goes deeper, the temporary poly-propylene netting at the face will be replaced by permanent areal support, similar to those used in the deep-level gold mining operations who are also exposed to rock-bursts and seismicity. As the PGM industry goes deeper, the risk of seismicity is greater and therefore support regimes need to be more robust at containing the effects of seismic damage: not only for FOGs due to seismicity, but also for gravity-induced failures.

Therefore, a decision to use ‘blast-on nets’ (BOM) in working areas has been taken by the senior Sibanye-Stillwater leadership team. This type of product is quite unique and is currently being manufactured in Switzerland. Durapraj expands, “The new product enables mesh installation right up to the face – one can even drape it on the face. The installation provides a greater areal coverage for the worker at the face, more so than the widely used temporary nets. It is installed before drilling commences, is not removed, is a permanent installation and also provides a measure of areal coverage for the cleaning operation in the mining cycle. The product has been rolled out at underground Sibanye-Stillwater PGM conventional operations. At Khuseleka shaft, where the stoping width is lower than 12m, the BOM roll-out necessitated a change in explosive type, as the original installations were being blasted out.

According to Durapraj, “Going forward, this new mesh promises to be a game changer, making a fundamental difference to the safety of the worker at the face, and hopefully creating a step change in FOG incidents, not only for the PGM sector, but for the mining industry in South Africa.”

Other indirect technological advances

Mutsvanga adds yet another technological solution to the discussion, “Sibanye-Stillwater also works with ground penetrating radar (GPR), which enables the identification of structures beyond the rock surface.”² The unit is called the Sub-Surface Profiler (SSP), which is an advanced version of a traditional GPR. It allows the user to identify geological structures deeper within the rock mass; those features that cannot be readily seen in the workings but may be the source of the next instability or FOG. He adds that traditional GPR has two practical challenges: one is that data interpretation can be tricky for the untrained and unskilled user, especially in the low-light underground environment, and two, when presented with an uneven rock surface, which is the reality most of the time, the scanned image is distorted, making identification of a geological structure at the correct position a challenge. However, with the appropriate training and experience, as well as upgrades to the SSP software and hardware (topographical correction), these challenges in interpretation will be resolved. Even so, when faced with these challenges, the product still gives ‘insight’ into the rockmass above the worker and the user may be able to stop a worker from being exposed to an unstable rockmass. Sibanye-Stillwater has seen the value of the technology, is using several units underground and has partnered with the SSP manufacturer and the Minerals Council South Africa to develop the product further.

Ndlovu also explains that in addition to the SSP, the rock engineer also has access to other technologies to assist both directly and indirectly in the design and day-to-day management of the FOG hazards. He summarises that “Numerical modelling forms an integral part of the safe mine design and optimisation process; Artificial Reality (AR)- and Virtual Reality (VR)-assisted training creates the surface and/or underground working areas where persons can interact with the hazards, provide mitigation for such hazard and note the consequences of his or her actions; drones can be used to investigate and analyse complex FOG incidents thereby allowing a more robust root-cause analysis for future prevention and mitigation of similar hazards; and even robotics such as SPOT³ can be used to gather information after a blast – rather than human intervention in a hazardous environment.”

Despite the advent of the new technologies, one must bear in mind that these products are sometimes expensive and may be niche, only for certain applications and under certain conditions, says Durapraj. However, this does not prevent us from seeking out, adapting and utilising these technologies. For example, as an industry, we are looking at Exoskeletons to aid the barring process. With the prolific rate as which technology is advancing, the rock engineer will have more tools at his disposal to assist the mining crews to be safer in their workplaces. Durapraj insists that, “Our workforce is crucial to our business and our business is to keep our people safe.” Mutsvanga too is emphatic – the human factor, behaviour and culture have a huge role to play in the outcomes in a hazardous underground environment and the quest to go home each day unharmed. Ndlovu adds, “Section 23 – the right to withdraw from a hazardous working environment – and SLAM: ‘Stop, look, assess and manage’ training come into play here, individuals are relied upon to show accountability and take responsibility for their safety in an emergency. The safety of employees overrules all other priorities.”

Durapraj concludes, “Annually, as a collective in the South African Mining Industry, we spend millions of hours underground. In this scenario, exposure to underground hazards is high, but through the use of specialist knowledge, on-site expertise, guidance from management and leadership, as well as innovative practices and tools, the reduction of and elimination of FOG injuries is possible.”

‘Blast-on nets’ by Geobrugg Made of a high-tensile steel wire, the Geobrugg solution is able to withstand impact energies of up to 10 000kJ to protect against rockfalls, landslides, debris flow and avalanches.4 The rhomboidal chain-link structure combined with the knotted ends of the mesh make handling and installation easier, with minimised overlap required. Mesh panels can be connected with T3 connection clips with a diameter of 4mm and a tensile strength of 1 770N/m2 – equivalent to the mesh itself. The high-tensile steel is around three times stronger than a mild-steel variety, while an Ultracoating® or Supercoating® – a 95 % Zn and 5 % Al compound – on the mesh offers corrosion protection. The mesh is very light in relation to its strength, making mechanical installation easy and safe – MINAX® 80/3 mesh weighs in the order of 1.45 kg/m. This mesh can be used as an alternative to time-consuming mesh and lacing practice and using the 4mm mesh, the need for shotcreting can also be eliminated. A mesh, with an 8mm cable on the leading edge facing the blasting front, during installation used and secured within 0.5m of the blast face, the blast-on mesh can also double up as a robust safety net that will remain in place during the blast. The mesh and anchor combination has proved successful in containing hanging wall instabilities.

References:

1. https://www.mosh.co.za/falls-of-ground/leading-practices/tarp-summary Triggered Action Response Plan (TARP) – TARP is derived from a mine’s Major Hazard Management Plan. It consists of a set of documented and known workplace hazards that need to be continuously checked

The level of risk is also pre-classified and the responsible person carrying out the inspection must perform according to this plan. Once the risk is identified, a remedial process is triggered which will escalate the problem to the level of responsibility that is required to deal with that risk in terms of the definition of the process. This TARP may be developed for any of the

major hazard areas within a mine, be they related to transport, rock, stored energy or falls of ground. The TARP system enhances the examination and making-safe process.

2. https://wafricanmining.co.za/2023/05/01/topographical-correction- visualising-beyond-the-surface-for-safety/
3. https://wafricanmining.co.za/2022/05/20/may-2022-cover-story- robotics-a-slow-adoption-and-yet-so-many-benefits/
4. https://www.geobrucom/en/Geobrugg-Safety-is-our-nature-114435. html

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