Two workers were at the maintenance shop, carrying out welding (hot work) on a metal tool (iron spear) used to break up ANFO lumps inside the MMU. After completing the first stage of the task, the welder
turned around to get a rag to clean the welded area, and at that moment, an explosion occurred. After the explosion, the workers left the area on their own. The metal tool broke into 4 larger pieces.