At around 2 p.m., in the foundry building of an aluminium plant, technicians smelt chlorine (Cl2) near the funnel between two kilns that supply a ladle of the wire drawing machine. The shift boss and an employee, wearing SCBA, measured a Cl2 concentration of 7 ppm in the workshop. The fixed detectors at ground level did not activate. The alarm display screen in the shift boss’ office also turned out to be defective (blank display). The machines were shut down, and the manual emergency shut-off for the gas cylinder room, located 100 m away, was closed. About 20 employees were evacuated, and the public emergency services were alerted. Traffic on the railway tracks, located just 200 m away from the plant, was halted as a preventive measure. A passenger train and two freight trains were also held up for about 30 minutes. The hose leak was isolated by closing and locking out 2 valves with padlocks. The fire brigade checked with the site personnel to ensure that the leak was under control, then lifted the alert at 3:25 p.m. The internal contingency plan was not initiated, and no environmental impact was reported.

The leaky hose, which had been replaced in October 2013 during scheduled (quarterly) preventive maintenance, had been tested with argon on 24/12/13 and with Cl2 on 09/01/14. No anomalies had been detected at that time. According to the facility operator, the accident may have been caused by a manufacturing or assembly defect or a metallurgical irregularity in one of the 2 flanges. The Inspection authorities for classified facilities requested that the facility operator consider several improvements:

• installation of a Cl2 detector at hose height (since rising hot gases limit the natural descent of Cl2) ;
• control of the 2 shut-off valves when chlorine is detected ;
• inclusion of an operational check of the alarm reporting display into the preventive maintenance plan ;
• installation of an emergency stop as close as possible to the installations.