Tracking personnel underground is technically challenging and therefore costly. Not with the zone coverage approach.
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Mining is a hazardous business in terms of workplace safety. Thanks to the myriad of HSE initiatives, working in mines got safer but "zero harm" has still to be achieved. Preventive measures like different mine design, excavation monitoring, implementation of autonomous systems and AI, explosion-proof equipment improved conditions but need a backup system in the event of an emergency.
Safety assistance systems have different layouts and designs. They not only differ by the technical set-up but also what they are capable to do. One aspect of a miner safety tracker solution is the idea of zone coverage. What does this mean? In general, zone monitoring focus on a specific zone and shows who is in that zone. This is different from the idea to track personnel wherever it is.
The difficulties to monitor personnel underground
Typically, a mine consists of several distinct areas: the entrance or access points, ramps for trucks and other equipment, blasting & loading levels, haulage level, exploration and drilling areas, ore passing, crushing and transporting installations as well as the above-ground production plant. Underground ramps and tunnels can sometimes grow to a network of several hundred kilometres in total. After a level has been exploited, it will be filled with waste material and abandoned. A mine is continuously moving - deeper and further with all necessary installations for production, transport and safety.
Monitoring miners underground is challenging because a mobile phone network or GPS is unavailable. Alternatively, operators create their own network. Intuitively, many think of a WiFi signal which would operators enable to locate a device within a certain radius of a specific WiFi router. The idea is feasible, but with one big disadvantage: you have to cover hundreds of kilometres, permanently installing and uninstalling infrastructure to keep with the progress of the mine, which is labour-intensive and costly.
The better option is to cover zones. Covering zones means monitoring the access to zones. Let's say you have ten sub-levels of each 1 km length. Instead of putting fibre and WiFi routers along 10km underground tracks, you only add reading devices at every sub-level entrance. By this, you will always know how many people entered, are still in a specific zone or left it. Workers equipped with transponders enable the system to locate them continuously. In case of an emergency, the rescue coordinator can immediately identify people in a zone at risk and act accordingly.
A safety assistance solution is needed that offers 100% reliability. In the case of an explosion, water breach, rockfall, vehicle accidents, cables of a WiFi system can get disrupted and are not available anymore. The chances this happens are higher the longer the cable network is. Reading devices of a zone monitoring system are connected by cable to a much shorter extent. These connections follow the main levels and ramps which are better maintained and monitored.
Illustration from: Numerical Investigation of Caved Rock Mass Friction and Fragmentation Change Influence on Gravity Flow Formation in Sublevel Caving - Scientific Figure on ResearchGate. Available from: https://www.researchgate.net/figure/Sublevel-caving-method-layout-1_fig1_315912296 [accessed 28 Dec, 2021]