Using a visual warning system to improve the safety of personnel, in an underground block cave mine, during seismic activity.
Earthquakes and other seismic events pose a significant risk to underground mines. Amplification of these hazards occurs in block or panel cave mining operations due to the nature of the mining method. Ensuring there are adequate warning systems on-site to protect personnel is critical.
The damage caused by activities such as earthquakes, small sidewall rock bursts or man-made seismicity, can affect underground mining operations and the associated surface infrastructure.
Challenge: IoT Automation was engaged by a large underground copper and gold block cave mine in Papua, Indonesia to develop a new system that would ensure all underground personnel are provided with real-time warning and evacuation information if a seismic event occurs.
Solution: Real-time visual communications provided by the Firefly Smart Lighting System (Firefly) to alert personnel to take actions during a hazardous event.
Like most underground block cave mines, this operation faces a variety of operational hazards including seismic, geotechnical, fire and gas exposure.
Seismic Monitoring in Underground Mines
Routine micro seismic monitoring in underground mines facilitates the accurate measurement of the frequency and magnitude of seismic activity. Real-time seismic monitoring of block cave underground mines is now an industry best practice. Source data is used to guide the prevention, control, and alerting to any potential rock mass volatilities that could result in damage to mine infrastructure or the potential endangerment to mine workers. Monitoring of regional and localised seismic activity is now widely adopted across block cave mines around the world.
Emergency Communications in Underground Mines
Most mines use an operational safety tool called a Trigger Action Response Plan (TARP). A TARP outlines a set of conditions and actions which mine management and supervisors must follow when abnormal and emergency events occur, including the steps which need to be taken as the various seismic threshold levels are breached.
Current mine communication processes to raise an underground emergency rely on verbal instructions. Traditionally, a series of alerts are sent to the workforce to trigger evacuation procedures in a seismically active area, including emails and radio instructions.
Limitations of these mechanisms are their reliance on timely delivery. Additionally, many international mining companies now employ both national and foreign workers. It is common for critical radio announcements to be in a language that many of the workforces do not understand. Further to this, emails are subject to delays or being overlooked; as a result, they are at best, a backup passage of information.
Another conventional method utilised by mines to raise awareness of an underground emergency is a stench gas system. This notification system uses the release of a strong-smelling gas into the mine’s ventilation system to trigger emergency response actions. However, a mine’s primary and secondary ventilation systems are regularly subjected to operational changes. These dynamic changes can reduce the effectiveness of the ventilation system in directing the stench gas smell to all areas of a mine, resulting in workers not receiving critical emergency information. Additionally, due to the widespread adoption of underground personnel wearing half or full-face respirators, the detection of these warning gases is again now not so assured.
All these communication mechanisms are vital for any underground operation. Each system is an added layer of protection built on top of the next method. The purpose of multiple systems is to ensure the safety of all personnel underground. However, even with these current systems, there is the potential for gaps in providing precise and real-time information to underground teams that are in the line of fire.
Current Seismic Alerts and Monitoring Underground
Real-time seismic monitoring at this underground block cave mine occurs via a permanent surface-and-underground installation of micro seismic stations. These stations contain a combination of calibrated geophone seismic sensors and data acquisition units. In turn, these instruments communicate with a central database located at the surface-based monitoring control centre.
This 24/7 geo-monitoring hub employs geoscience staff working with automated software, to interpret the critical flow of seismic data from the mine. Information learnt from this team is used to inform senior management and underground workers of any emerging seismic risks or trends.
The geoscience team is also responsible for managing the demarcation of the safe and unsafe work areas associated with the advancing cave front, detected seismicity or planned undercutting activities. Previously, under the control of the geoscience team, hazardous sections of the underground mine were zoned off using a combination of wall signage, sign-in log books, barricades and strobe lights. Additionally, updated mine plans with colour-coded areas detailing different safe zones on each level were dispersed to the underground teams via email.
Over recent years the operational data provided by the geoscience team has become ever more critical to the safe and optimised running of the mine. This shift necessitated that the geoscience team required an alerting system that would provide a more effective and real-time method of detailing the current seismic state of the mine. If and when a seismic event was to occur, there needed to be a real-time mechanism to notify the underground workers as to what actions they should be taking. The new system was required to provide alerting information to the localised geographical location where the seismic risks occurred, instead of evacuating the whole mine or an entire level for a small localised event. Therefore, the system needed to be flexible enough to be able to provide relevant warning or evacuation information, as required to; a single panel drive, a pre-defined geographical exclusion zone, level wide, or mine wide.
Any new system would also need to have the ability to be customised around their current emergency, operational and geoscience systems, processes and software applications.
Installing Firefly Smart Lighting as a Seismic Warning System
In December 2018, the underground operations implemented the Firefly Smart Lighting System (Firefly) to provide real-time alerts to the underground workforce. Firefly offers visual and audible prompts to inform underground workers of a safe or unsafe work zone, that seismic level thresholds have been crossed or that a mine emergency has occurred.
IoT Automation worked alongside the geoscience and electrical teams to implement the new smart lighting system. More importantly, incorporate Firefly into their current processes and systems. 1,200 Firefly lights were installed across 21kms of the mine’s undercut and extraction level tunnels. The Firefly lighting control software server was installed at the surface data centre. The Firefly lighting control application is used to configure, monitor and manage the entire Firefly smart lighting system. This web-based application is also the key user interface for triggering the underground emergency or evacuation alerts.
The Firefly Smart Lighting System uses intelligent illumination to communicate critical information to underground mine workers. The Firefly software can be integrated into the mine’s seismic monitoring software to provide automatically triggered real-time visual and audible communications to the underground workforce. Also, the Firefly lighting modules can wirelessly connect to a mine’s geotechnical instruments.
How Firefly was Installed Underground
On the extraction level of this block cave mine, the draw points are spaced at 20m intervals along the panel drives. The Firefly lighting modules are installed adjacent to each draw point at the same 20m intervals. The Firefly lights are daisy-chained together by an armoured four core instrument cable which connects each string of Firefly lights back to the Firefly control panel. Which in turn is networked back via the mine’s existing network infrastructure, to the Firefly central server. As an added functionality of the Firefly lighting modules, the Bluetooth radio of each Firefly light is utilised to provide a wireless connection to the mine’s geotechnical extensometers (MPBX), which are correspondingly also installed at 20m intervals into the pillars of each draw point along the panel drives.
From there the MPBX data is then transferred back along the Firefly wired network to the Firefly central server and then pushed out to the mine’s geotechnical monitoring database. This transfer provides a robust and reliable data backhaul network for the mine’s critical geotechnical data information.
The mine now utilises the map-based Firefly Lighting Control Application combined with the Firefly Smart Lighting Network to accurately control and apply their seismic response plans to the underground mine workings. The software-controlled Firefly lighting uses various lighting colours and lighting modes (flashing/chasing/solid) to indicate safe, unsafe and seismic work zones in an underground mine.
This flexible system enables the mine to trigger immediate actions and systematically update zones on a daily or weekly basis. The mine can create exclusion zones around the cave front, close access to specific drives or shut down entire levels during undercut blasting. Additionally, in an emergency, the system will initiate mine-wide evacuations. While also providing guidance lighting, to direct mine workers as to the correct route they should take, to arrive at a refuge chamber or to access the primary or secondary escape ways.
Benefits of Smart Lighting for Seismic Warning
Firefly empowers personnel to have the best chance of removing themselves and their equipment from an at-risk seismic area of the mine. This mining operation has seen the benefits of using Firefly, through;
Reduction in Workforce Exposure
The Firefly alerting system ensured effective removal of personnel from areas of increased seismic activity or regions affected by a seismic event with minimal delay. Reducing the workforce’s exposure to seismic risk and hazardous events.
The system is also used to prevent personnel from entering an unsafe area isolated due to the advancing cave front, hydrofracturing, or other high-risk mining activities.
Rapid and Automatic Response
Utilising the Firefly Smart Lighting Network throughout the mines underground working, the geoscience team can now provide real-time and immediate seismic threshold trigger response outcomes. This direct and controlled visual and siren communication mechanism enables the mine to reduce the exposure of their underground workers to seismic risks. By providing precise and immediate information as to whether the areas they are working in are safe, unsafe, or if evacuation is required.
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