At around 1:00 p.m., an explosion followed by a plume of smoke occurred at chemical plant. The facilities were safely shut off and the production units where shut down. The operator implemented the site’s internal emergency plan. An employee and a contractor complained of tinnitus. They were examined on site but nothing abnormal was found. The operator informed local residents, inspection services, neighbouring businesses, and the town hall. The internal emergency plan was lifted at around 3:00 p.m.

A mental health response unit was set up to provide support to employees in shock.

The explosion was caused by an expansion bellows that ruptured on an air pipe. The tie bolts used to fasten the bellows to the pipe were subjected to strain, causing them to distort and then, after 56 days, rupture. This strain was caused by the following situations:

• the blocked expansion of the pipe transferred the stresses in the tie bolts;
• the tie bolts were not made of the strongest material;
• the expansion fitting was lagged, causing the temperature of the tie bolts to increase, fatiguing them and leading to creep.

A bellows had been ordered in early 2017. The supplier delivered a bellows that had a new design (five tie bolts instead of four) and a different component material to the one usually used. The operator was told by the supplier that the new design met the required specifications.

These specifications indicate a maximum displacement of 300 mm. An analysis, showed that the new bellows could only compensate for 65 mm.

Following the event, the operator:

• changed the line’s geometry in order to replace the bellows by an expansion loop;
• checked the plant’s other bellows;
• updated the change management procedure;
• incorporated changes to supplier parts without changes to the specifications book into the change management procedure.

The total cost of the work is 1 138 k €. The operator cannot produce ammonia for 32 days, equivalent to a loss of revenue of 8.7 M€.