In a factory specialised in animal feed, an explosion followed by a fire occurred in one of the silos for storing crushed raw materials, where an employee with a subcontracted firm was performing an arc welding operation. The full set of installations were shut down as an emergency measure, and the seriously injured worker was evacuated from the site. The continuation of filling operations on the other containers had caused dust to spill into the silo undergoing repairs via a rotary drum connected to the network of silo feed pipes. The air-dust mix exploded in contact with the welder’s electric arc, which was included in the tasks assigned to the subcontractor. The classified facilities inspector’s analysis of the prevention plan plus the nature of operations conducted preliminary to these works revealed, on the one hand, noncompliance with several procedural steps that had proven inadequate; on the other hand were organisational shortfalls or lapses relative to the control, knowledge and execution of these operations. More specifically, the hot work permit submitted by the technician performing these safety-related works eliminated all 2nd-level controls. The site operator was issued an injunction to revise facility procedures.