At around 11 p.m., in a plastic manufacturing plant, a cloud of carbon tetrachloride (CCl4) and hydrogen chloride (HCl) intoxicates 2 technicians. They were evacuated and given oxygen. A security perimeter was set up. One employee was sent home. The other, remained under observation all morning, was granted medical leave of absence for more than a month.
The lack of efficient treatment of gaseous effluents from a reactor, using a scrubber, led to the release of toxic substances into the workshop’s atmosphere. The reactor concerned was shut down for maintenance on its cooling system. In this configuration, it was kept under load (a mixture of CCl4, HCl, N2O and NO2) and its vapour space was conveyed to a scrubber for treatment. In normal operation, the gaseous releases are treated by a scrubbing column. When the reactor was restarted, the vapour space was no longer conveyed to the scrubbing column for treatment. To direct the reactor vents towards the column, the technician had to manipulate two valves. For one of the valves, it was difficult to see its open/closed position. A control rod is used to operate the valve, but it can be disconnected. Furthermore, the valve’s position is not represented on the control room panels and the reactor restart procedure does not include valve position control. The valve directing the vents to the scrubber was therefore left open, resulting in excess gas in the scrubber, which cannot process it during normal operation, and therefore resulted in degassing to the atmosphere. The lack of CCl4 and HCl detectors near the scrubber led to the intoxication of the technicians present.
Following this incident, the facility operator:
- communicated information about the accident to the all the crews,
- implemented dual control of the valves when changing the orientation of the reactor’s vents: on site and in the control room,
- initiated a study to prevent reactor start-up if the vents are not properly oriented,
- implemented a working group to improve practices and reinforce job training.
