Assessing an automated mining operation with STPA

Autonomous mining reshapes contemporary mining practices as it plays an increasing role in bringing value to customers. The benefits encompass improvements in operational efficiency, safety, and process reliability while offering flexible maintenance programs that reduce downtime and costs. Mine automation systems cover a wide range of automation, from individual control cabinets to controlling entire fleets. However, the growing complexity and functionality of these systems introduce new risks, necessitating a comprehensive safety analysis. Traditional hazard analysis methods, which examine system components separately and in isolation, are no longer adequate. In complex systems, such as mine automation systems, losses may occur not only due to component failures but rather because of unpredictable and undesired interactions among system elements. Rooted in system theory, Systems-Theoretic Process Analysis (STPA) can address this complex, non-linear way of how losses can arise.

This study employs STPA to examine its suitability for the mine automation industry by assessing a mining pit's automated and remotely operated drill rig fleet. Additionally, the research explores the potential of STPA for identifying system requirements and safety goals in the context of mine automation systems. System elements of the examined use case are three automated drill rigs and a teleoperation station. The analysis deals with a typical daily maintenance use case when the mode of operation must be changed as the maintenance person approaches the drill rig and returns.

STPA, is implemented in four stages: defining the analysis’ purpose, modelling the control structure, identifying the unsafe control actions, and finally describing loss scenarios. In comparison to traditional hazard and safety analysis tools, STPA gives special attention to control actions by dedicating Step 3 to identifying how assumingly suitable and safe control actions can become unsafe.

Results show that STPA, which views safety as a control problem, provides valuable insights into the dynamic interactions between the remote operator in the teleoperation station and the on-site maintenance personnel using the drill rig's onboard control system and the control cabinet at the site. The use-case analysis of six control actions revealed 15 possible unsafe control actions and over 40 possible loss scenarios. A significant share of loss scenarios is related to human - machine interactions. Concretely, the study highlighted the importance of communication between the maintenance person and the remote operator, emphasizing the need to prevent communication and
connectivity problems. Additionally, challenges related to the indication of the operating mode of the drill rig and its transition as well as the location of on-site control cabinet affecting safety were identified. Proposals were made for clearer communication through clearer operating mode indication. Further, better site overview and visibility could prevent unintended drill rig approaches during drill rig’s automatic operation. While the results are not of technical nature, they can aid in creating a safe work environment and understanding factors affecting the work at the site. STPA proved to deliver valuable input for discussions during system’s conceptual design phase. Furthermore, the tool appears to contribute to assessing planed system design modifications as well as reassessing already existing systems.

This research has been conducted as a part of the “Future Electrified Mobile Machines” (FEMMa) project, which is mainly funded by Business Finland.