The electrical circuit powered by a transformer short-circuited several times after the facilities at a paper mill were put back into service after a scheduled shutdown. Electricians were therefore brought in to check and clean the facilities powered by the transformer. Three of them were burned by an electric arc while working.
Multiple factors contributed to the accident:
- condensation due to a significant amount of steam from the process
- unsealed cable duct
- inadequate sealing of the connection box in the utility tunnel
- team management failure: no exploration manager was appointed
- the technical documentation was not consulted
- failure to follow standards of workmanship: the workers removed a box allowing access to bare conductors.
To prevent the incident recurring, a number of technical actions were immediately implemented when the mill was restarted on 24 March:
- steam migration study. The process pre-heating procedure was modified and the drains were moved outside the building
- caulking of cable duct were insulated with glass-wool panels
- fireproof sealant was applied to one of the boxes inside the utility tunnel
- a study was initiated to remove the boxes from the busbar ducts and fit insulation all the way to the bottom of the cabinets. If this is not feasible, the possibility of a mechanical lock that only opens when the box is de-energised will be studied
- the electrical department is looking into revising the methods used when performing emergency work. Everyone in the department will receive increased training in distribution networks.
Other improvements have been identified: the utility tunnel is now lighted and the boxes are fitted with ID labels. The property damage and operating losses were estimated at €2m.