In an industrial gas manufacturing facility, a 5-litre cylinder of compressed chlorine (Cl2, toxic gas) was placed horizontally in a reinforced protective enclosure for subsequent emptying and repair, as its valve was clogged. The cylinder began to leak as the two operators were installing the valve’s handwheel and the union cap ring allowing the valve to be removed once in the closed enclosure. The operators inhaled the Cl2. One was able to exit the workshop and don a self-contained breathing apparatus and prepare the flooding tank, while the other operator unsuccessfully tried to close the valve. He attempted to don the self-contained breathing apparatus but, unable to do so, returned to the cylinder to unscrew the flange bolts. The second operator, wearing the breathing apparatus, removed the flange and placed the cylinder in the water tank. The leak into the open air lasted 15 minutes, resulting in the release of 6 kg of Cl2. A specialised company pumped 200 l of acidic chlorinated water from the tank for subsequent neutralisation. The emergency services, having arrived at the site 15 minutes after the start of the leak, detected no trace of Cl2 in the atmosphere or the wastewater network near the site. The two operators were examined at the hospital and then released during the day.

The analysis of the accident showed that the cylinder being placed in the horizontal position caused it to become unclogged. The liquid Cl2 had attacked the solid product clogging the valve’s opening. The valve had remained blocked open by corrosion, despite the efforts made to close it. After attempting to drain the cylinder before placing it in the protective enclosure, the operators had not placed the safety plug on the valve before laying the cylinder down. The current instructions had not required that the safety plug be installed before placement in the enclosure. The operator implemented the following corrective measures:

• modification of the operating instructions for the systematic installation of the safety plug on the valve before placement in the protective enclosure,
• modification of the personnel’s safety procedures in the event a valve is clogged on a cylinder containing toxic gas,
• improvement of the layout of the self-contained breathing apparatus room and the ergonomics of the breathing apparatus storage cabinets to make it easy for operators to equip themselves,
• enhanced training on how to wear and operate self-contained breathing apparatus for the operators handling cylinders containing toxic gases.