In a foundry, the operator controlling an electromagnetic induction furnace attempted to bring it down after filling a ladle on a cart. The furnace continued to rise. At 8:23 p.m., the entirety of its contents, 9 tons of molten metal, spilled onto the ground and onto the cart causing several fires to break out. The smelter, controlling the installation, received second-degree burns on the forearms due to the backsplash. Employees attempted to extinguish the fire with fire extinguishers and then raised the alarm. The internal emergency plan was activated and the 200 employees were evacuated. Firefighters disconnected the power sources and put out the fire. They transported the burn victim and another employee suffering from smoke inhalation to the hospital. The intervention was concluded at 3 a.m. The cart and the control booth were destroyed; the furnace was damaged, and the 100 m² of slab was weakened. Activity at the site resumed the following day. The cart was removed, and the slab was secured. The Classified Facilities Inspection Authorities visited the site.

While adjusting the furnace’s lowering speed on the controller, the operator had entered a positive parameter instead of a negative parameter. This parameter caused the furnace’s direction of descent to be reversed. The non-deactivation of the controller’s maintenance mode meant that these parameters could be modified. However, given that the “metal jet cut-off” pushbutton was connected to the same parameter as that of the furnace’s descent, the situation could not be corrected.

The design of the supervisory software meant that any operator could modify the parameters. Moreover, there was no safety lock, and it was possible to enter a parameter inconsistent with the requested movement.

Before restarting the installation, the operator modified the controller in the following manner:

• creation of a maintenance mode password with limited distribution to authorised maintenance professionals,
• implementation of a one-minute “time-out” on the maintenance mode login installation of a lock, to avoid erroneous values being acquired by the PLC,
• implementation of a fixed parameter value dedicated to the “metal jet cut-off” function,
• replacement of the pulse-type “metal jet cut-off” pushbutton by a hooking-type pushbutton to prioritise its action over that of the joystick on all furnaces,
• access to the PLC cabinets reserved for maintenance professionals.

In the long term, the operator plans:

• to provide a fixed indication of the current mode on the screen (maintenance or production),
• to remove the sign (+/-) on the furnace movement management parameters,
• to install a mechanical and secured purge valve, independent of the automated controller, in the control booths to raise or lower the furnace in case of emergency,
• to protect the smelter in the booth and reinforce its P.P.E.