Inside a pharmaceuticals plant, the rupture disc on the “process” scrubber burst around 2:40 pm, causing a release of 3.6 m³ of gaseous hydrogen chloride (HCl).
The “process” scrubber was a soda neutralisation unit capable of recovering vapours from the building’s various synthesis reactor vents before routing to a treatment unit. Given that a new batch contained a high “fines” concentration, a flame arrestor located on the collection circuit became heavily clogged, thus leading to a pressure surge in the downstream scrubber and a bursting of its disc, which had been calibrated at 150 mbar. Two technicians performing maintenance nearby sounded the alarm via the intercom. The internal emergency plan was activated: all access paths to the zone were closed, personnel in adjacent buildings were confined indoors (air suction and intakes shut down), and 1 pair of responders wearing self-breathing apparatuses carried out a reconnaissance mission. A 100-m safety perimeter was set up and the site’s utility lines cut off. HCl measurements were recorded using portable analysers, which indicated zero risk (the cloud had diluted over some 20 metres in just a few minutes). The rupture disc was replaced and production facilities could be restarted 90 min after the incident.
This event highlighted 2 points relative to the processing of alarms:
- pressure was to be measured upstream of the flame arrestors so as to detect clogging as early as possible, but the guideline did not specify the course of action should the threshold be exceeded;
- HCl detectors in the vicinity of the scrubber were triggered, but no guideline stipulated the actions to implement when processing the information output by this alarm.
Moreover, no guideline discussed placing the upstream production installations into safe operating mode in the event of an incident (e.g. regarding the scrubber).
The plant operator thoroughly verified the scrubber condition (drainage and bleeding) and scheduled the annual inspection. The condition of flame arrestors was also checked and a guideline issued to address their dismantling, including the points to be verified prior to reassembly. The operator stressed the systematic monitoring and cleaning of flame arrestors in the presence of clogging; these points were incorporated into the manufacturing files. Moreover, a servo-control was inserted between production and pressure measurement. The plant’s internal emergency plan was updated to integrate toxic effects and availability of self-breathing apparatuses in 2 of the facility’s protected sectors.
