In a mineral water bottling plant, the company’s maintenance crew and subcontractors were taking advantage of the scheduled production shutdown during the weekend to intervene on the blocked wastewater networks. Noting that there was no inspection hatch in the underground service duct, the technicians decided to create an opening. They took advantage of the operation to cut off an old, rinsed and vented caustic soda pipe.

The pipe was located at the height of 30 cm. While attempting to cut it, an employee erroneously cut a stainless steel nitric acid pipe located between the caustic soda pipe and the new pipe. Having been sprayed with acid, he went to use the safety shower. A subcontractor who was performing a welding operation nearby tried to leave the service duct, but went in the wrong direction and found himself against an emergency exit that had been locked, and was out of service, following a flood. He retraced his footsteps and passed through a yellow cloud of acidic vapours while protecting his respiratory tract with his hand. The emergency rescue services evacuated the two men to the hospital where they were treated for second-degree burns. They were released in the afternoon.

The other operations in the plant were shut down and the soda valves were closed 10 minutes after the accident. The valves for the acid and two other chemical products conveyed via the service duct were closed an hour later, at the same time as the electrical power supply to two lift pumps for the pit in the bottom of the service duct.

The firefighters drained the pipes, pumped the acid and ventilated the service duct. The intervention was terminated at 10 p.m.

The responders were qualified to intervene and were knowledgeable of the chemical hazards. The decision to cut off the soda line was made without prior risk analysis, outside the scope of a separate intervention, which had been approved by a written permit. The acid and soda lines had been properly marked. The wrong tools were used for the cutting operation (a 230 mm diameter angle grinder was used to cut a 20 mm diameter pipe).

The operator set up a work permit for work carried out in-house, identical to that for work performed by subcontractors. A fluid shut-off procedure was also implemented in case of intervention. The proper marking of emergency exits was also reinforced with arrow markings on the floor. The blocked exit was put back into service, and the flooding risk was taken into account. Signage indicating the procedure during an intervention in the service duct was displayed on the access doors. A chemical hazards refresher course was scheduled for the operators. Moreover, the operator integrated a significant concentration of CO2 (in a confined environment) into its risk analysis and reinforced the means of detection. A long-term consideration is being given to the risk of a release into a nearby river (deviation to a pre-treatment station, pH sensor installation, etc.). The installation of piping in the service duct, which currently houses a 20 kV line along its ceiling, drinking water at the top, chemical products and wastewater underneath and computer cables, is also being studied.