At around 6:45 p.m., bromine vapours were released as aqueous brominated effluent was starting to be transferred in a non-pressurised vessel at a fine chemicals plant. The technician who had manually started the transfer pump saw a large orangish cloud form. He stopped the pump, and the emissions ceased, after about 20 seconds. He then neutralised the bromine vapours using an ammonia solution. A fixed detector near the emission point set off an alarm. The plant’s fire-fighters arrived. They were joined by the external firefighters, who had been alerted by local residents. By the time they arrived, the cloud had dispersed. The internal medical service gave oxygen to the technician exposed to bromine. The leak was estimated at 3.9 kg.

The effluent had not been completely neutralised prior to its transfer

The release was caused by an excessive concentration of bromine in the effluent arriving from the reboiler of a fractionating column. According to the plant’s operating procedures, residual bromine is supposed to be neutralised there with potassium sulphite. The effluents’ colour is supposed to be visually checked to ensure that it has been fully neutralised before being transferred. Prior to the incident, the facilities had been drained in preparation for the unit’s shutdown. The reboiler contained more effluent (and thus bromine) than usual. The standard amount of potassium sulphite was insufficient to neutralize all the bromine. The technician did not check the effluent’s colour via the reboiler’s viewing port. The vapours were released when the effluent arrived in the first non-sealed vessel of the transfer circuit leading to a storage tank.

Corrective actions

The operator:

• drew up more precise and detailed operating procedures;
• added a signature line confirming that the end of neutralization has been visually checked;
• changed the facilities’ shutdown procedure.