In a wood panel manufacturing plant being restarted after 9 days of technical shut-down, a fire alarm on one of the 3 driers stopped the installations after the time threshold was exceeded (10 seconds of continuous alarm) and the detection of sparks (infrared sensors). The operators, assisted by the safety officer on duty, searched the cause of the alarm for 2.5 hours and discovered embers in a duct above the cyclones. A fire nozzle was set up to spray down the inside of the duct via an inspection hatch, accessible using a ladder from an overhead catwalk. The spraying operation had been underway for just 2 minutes when the explosion occurred. The operator holding the fire nozzle lost his balance and fell 9.5 meters to his death. The explosion vents were destroyed. An expert assessment of the accident attributed the explosion to the presence of CO producing a smouldering fire in the final portion of the drier, near the explosion vents. The fire was caused by welding operations that had been undertaken 48 hours earlier.