On March 23, 2005, the raffinate splitter process was being restarted after a turndown. The unit had been shut down February 21 so that the tower could be drained, purged, and steam cleaned to remove residues.

Apparently nothing had been done to check level sensors installed in the tower, and a sight glass mounted at the bottom that had been too dirty to use for some years was untouched. Operators preparing for the restart had reported that a pressure vent valve on the reflux drum could not be operated from the control room, but this was not fixed either.

According to BP procedures, that single valve malfunction alone should have prevented restarting the unit until it could be resolved.

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