The conveyor belt represents one of the most commonly used methods of transporting bulk materials today. As highlighted multiple times in research, the moving parts are a critical issue causing accidents and injuries and several of these are strictly related to the opportunity to enter in working zones during maintenance activities, considered high-risk activity due to the nature of the job. For these reasons, maintenance operations have to be carefully planned during the design phase, with the adoption of appropriate safety measures for the maintenance crew and other people present in the area. On the other hand, preventative measures have to be put in action for maintenance operations and daily work. Analysing the accident reports related to the crushing and milling plants obtained from the several data bases and identifying with a Cause-Consequences analysis the root causes of an injury occurred in an Italian quarry, the paper underlines critical issues of the conveyor belts during maintenance operations, identifies common errors in the system management that affect the workers' safety and proposes an approach in order to improve the maintainability and the safety during the design phase.