At 2:30 p.m., in a glass factory, an excavator accidentally damaged a buried natural gas pipe made of high-density polyethene (4 bar). The damage resulted in gas leaking into the atmosphere for 10 minutes; the time it took to close the shut-off valves. The job site was evacuated, and a safety perimeter was set up. The atmosphere inside and outside the adjacent building and the area around the excavation was checked. The piping was put back into service two days later.

Numerous tasks subcontracted

According to the initial elements collected following the event:

• the earthmoving operations, initially assigned to a first company, was then subcontracted to another public works company. The site’s operator had also subcontracted job site security duties to a specialised company;
• the prime contractor (different from the operator) had given the first subcontractor an excavation drawing, but it didn’t cover the entire construction area;
• the marking/staking out of the utilities had not been completed before the work began, and risk analysis had not been conducted at the site;
• while digging, the excavator operator noticed the warning mesh indicating a buried gas line. He stopped digging and asked his site manager what to do. The latter (recently hired) reportedly indicated that the section of piping in question was abandoned, and therefore not under pressure and that the machine operator could continue digging. This confusion may be explained by the fact that another crew from the public works company had intervened a week earlier, in the same sector, on some abandoned pipelines.

Measures taken

To prevent such an event from reoccurring, the subcontractor in charge of job site safety must:

• provide a daily time slot for external companies to conduct their risk analyses, in the presence of the principal;
• issue a new risk analysis and/or excavation permit for each new task and for each external company;
• include the facility operator of the Seveso classified site in the approval circuit for all pre-work excavation permits;
• conduct an audit at the start of each new task.

Finally, the Inspection authorities for classified facilities requested that the operator improve the supervision and oversight of all its subcontractors, including those dedicated to safety. As such, the operator undertakes to conduct unannounced inspections itself in order to ensure the practical application of the safety rules defined in its site procedures.