At a Seveso-classified chlorine chemical plant that had been shut down for two weeks, two subcontractor employees were cutting a purge pipe on a hydrogen manifold in the chlorine electrolysis room while a manufacturing operator was purging the brine circuit (brine is used as a raw material in chlorine production). A through-cut caused an explosion inside the hydrogen manifold that blew apart the rubber sleeves connecting the manifold to the electrolysis cells. The operator was knocked down by the explosion and sustained injuries to the face and shoulder from flying pieces of sleeve and plastic. The facility was placed in a safe condition and the fire-fighters were alerted. The injured operator was taken to hospital by helicopter. The two subcontractor employees, shaken by the blast, were treated in the site’s infirmary. The injured operator, who sustained neither fractures nor trauma, was released the same evening. The plant operator issued a press release.

The work authorisation issued to the subcontractor had not identified the risk of hydrogen in the manifold, which had been purged with nitrogen when the electrolysis room was shut down in December. Also, due to a misunderstanding about the exact location of the cut, the work authorisation, did not call for closing the valve used to isolate the manifold from the hydrogen condensate pipe.  Air brought in while the electrolysis cells were opened and hydrogen from insufficient nitrogen scavenging or several weeks of hydrogen desorption from the steel of the manifold created an explosive mixture that ignited during the cutting operation.

The plant operator has begun implementing regular audits of the risk analyses that are conducted when work authorisations are issued.