At 10.30 am., a release of chlorine occurred from a vent scrubber as a result of overfilling of open-air storage tank from road tanker.

The road tanker containing 18 t of chlorine arrived on site at 8.30 am. The transfer into a 46 t tank proceeded without problem until 9.30 am : as the supervisor left the area to take a sample to the laboratory, the tank overfilled and liquid chlorine entered the vent pipe into the scrubber. However, the scrubber (using caustic soda) was soon insufficient and chlorine was released to the atmosphere : 5 employees exposed to the gas experienced respiratory problems, they were admitted to local hospital for observation overnight. The On-site emergency plan activated to some extent but not completely successfully (no emergency alarm sounded, confused response…). Tanker driver closed the tanker valves wearing a breathing apparatus.

The accident analysis showed that :

• the load cell under the tanks were out of calibration (reading 7.3 t lower) due to heavy corrosion and neglect
• the high level alarm was activated by the load cell (no discrepancy between process/safety sensors)
• the gas detector at scrubber outlet were out of working order
• the technicians received inadequate instruction and training.

The inspections thus noted failures in operating procedures/instruction, operator training, emergency procedures, instruction, training and practice as well as management failure in the SMS.

The operator organised periodical inspection, servicing and calibration of critical instruments, wrote precise operating instructions for safety critical activities and started proper operator training. He revised the emergency procedures with adequate instruction and training of all staff and regular practices, drills and exercises.