Bezpieczeństwo Pracy i Ochrona Środowiska w Górnictwie Number 06/2023

To meet the requirements of effective regulations, underground mining plants are obligated to ensure short circuit and overload protection in their power systems, in line with Polish Standards. However, Polish Standards include the PN-G-*** group of standards which apply to power systems in underground mines, as well as European Standards: PN-EN 50628:2016 and PN-EN 60909-0:2016-09, which set out different requirements for the same issues. Considering changes in effective regulations and technical solutions in mining, contrary to European Standards, the standards from the PN-G-*** group lack cohesion with standards pertaining to non-mining power equipment and systems, and some of their provisions are inadequate to the character of phenomena occurring in the circuits they are bound to protect. There are many areas where European Standards deviate from the design principles adopted in existing power systems in the underground excavations of Polish mines. A comparison of the requirements from the said group of PN-G-*** standards and European Standards indicated that the settings of short circuit protections calculated on the basis of European Polish Standards [1, 2] can be higher than the values calculated on the basis of the mining standard [3]. This could limit the number of unnecessary shutdowns of power equipment used in underground mine excavations, particularly in explosive areas, which is particularly important for improving the operational safety and production efficiency in mining plants.

The article focuses on issues encountered in the execution of a crosscut in a fault zone with a 120 m drop, and contains a description of the technology used by TAURON Wydobycie S.A. ZG “Sobieski” to seal the rock formations surrounding the excavation. When the crosscut reached a fault, the excavation was buried with loose debris from the neighboring rock formations. Due to simultaneous inflow of large amounts of water, the drainage system was prepared to guarantee water discharge exceeding the projected inflow by 50%. In order to fulfill the assumptions for the developed technology for safe passage through the fault zone, 7 holes were drilled to create drainage and subsequently lower hydrostatic pressure by 0.3 MPa. After that, crosscut drilling proceeded in strictly controlled and interrelated technological phases. These phases included reinforcing the rock mass with mineral binder through pre-drilled holes, and then by completing repeated cycles of excavation drillings in the fault zone, consisting of: drilling, rock mass reinforcement with binder injections and steel rod or self-tapping anchor piloting, building consecutive frames under the existing lining, and pumping mineral binder between individual lining layers.

The article presents dangerous events in opencast mines in the years 2012-2022, in particular cases of finding unexploded ordnance from the 1st (ZEK "Bobrowniki") and the 2nd World War ("Kotlarnia" Sand Mine). In order to eliminate this threat, the mining supervision authority has developed the following actions, which as "good practice" should permanently become part of the canon of conduct of every mining entrepreneur: (1) Analysis of the history of the mining area in aspect warfare; (2) Preparation an of safe work instructions in case of finding unexploded ordnance; (3) Application of procedures ensuring the safety of employes and bystanders, i.e.: (i) suspension of further work in the threated area; (ii) warning the people working nearby; (iii) retreat to a safe distance (including machines if possible); (iv) securing access to threated area; (v) supervising (from the safe distance) the threated area until the arrival of Police/sappers; (vi) elimination of the threat by specialized services; (4) Elimination of future threats, i.e. sapper reconnaissance and clearing the area of identified explosives and dangerous objects.