At 11 am in a steel mill specialising in galvanising, an explosion ripped through a sheet preheating furnace that had been shut down the previous evening for annual maintenance work. The zinc crucible’s draining operations was completed and the hydrogen purge operation (hydrogen is used with N2 to form the furnace’s reducing atmosphere), which had been started 6 hours earlier, was underway when the accident happened. The 4 employees present were not injured, although were hospitalised for hearing tests. No impact outside the site was reported.

The blast was attributed to the valve on the backup H2 tank and the by-pass on the furnace’s supply line not being closed; hot points ignited the explosive atmosphere. Following the accident, the operator modified the procedures concerning these operations (blinding of the by-pass and leak test, modification of the valve of the back-up H2 circuit to allow lock-out capability…) and completed the intervention procedure.