On a Saturday afternoon in a plant producing resorcinol, a technician was simultaneously using the normal transfer line and the emergency line to more quickly fill the 1502 reservoir with oleum (fuming sulphuric acid). During the filling step, he was preparing calcium carbonate. When his shift ended at 2 pm, he left the plant but forgot to turn off the emergency line pump. At 2:13 then at 2:18, two visual alarms indicated a high level had been reached. At 3:12, vapours were emanating from the reservoir, and at 4:15 employees identified the emanations and informed their superiors. The personnel, believing the leak to be on the line, blew in air. As this release continued, the plant was evacuated and the fire station was called at 4:55.
The authorities closed roads and confined or evacuated 2,500 local residents. At 4:58 pm, the extinction system was activated in the room in order to dilute the oleum, but this effort failed. A team wearing anti-chemical suits carried out a survey to determine the source of this release. The cloud was too dense and the team could not advance inside the building. The emergency crew however noted that oleum was dripping on them from the top of reservoir 1502 and deduced that a pump was still running. They decided to cut the electrical supply but were unable to safely reach the electrical control room due to overflow water. The pump could not be remotely shut down before 7 pm. At 2 am, atmospheric measurements revealed no trace of product, and neighbours were allowed back into their homes. During this intervention, 1 rescue worker inhaled vapours. An investigation was initiated by the CSB Federal Agency overseeing chemical accidents.
The CSB identified several irregularities in the incident report. When the level was high in the 1502 reservoir, the normal transfer pump shut down but the emergency pump remained on. Moreover, only the visual alarm was functioning, as the sound alarm had been inoperable for several months. No procedure called for verifying their operations. Also, the emergency line was not equipped with a remote control.
Since the end of the 1980’s, the company had been employing a 3rd person in this unit, meaning that the personnel no longer had to hurry to fill the reservoirs while preparing sodium carbonate, meaning that use of the emergency line was no longer necessary. Nonetheless, the technicians continued to use this backup line and trained new hires by oral instructions, since no written procedures had been drawn up. Plant management was perfectly aware of this practice on weekends and tolerated it given that it allowed filling the storage tanks immediately upon the Monday oleum delivery.
During the risk analyses, the emergency line had been taken into account to the same extent as the normal line even though it had not been equipped with the same safety features (e.g. automatic shutoff upon high level detection).
