Redundant emergency shutdown
30 The tank mimics on the screen showed a red ‘stop’ emergency shutdown button. Use of this was meant to close all tank side valves. Unbeknown to a number of the supervisors this was not working and had never been fitted into the system. Had it worked it may have provided a useful emergency procedure although it may have taken several minutes for the valves to close. This issue
is indicative of poor management control where supervisors did not appreciate the redundancy of the ‘stop’ button and Motherwell staff never tested it. This meant that there was no proactive facility on the site to close down two (UKOP) of the three incoming pipelines. The Finaline had an emergency shutdown button accessible in the site control room.
System security
31 While there is no indication that it had any bearing on the incident, the security arrangements on the ATG system were lacking. It had its own built-in security system but this had been set so that all control room staff could modify any parameter including being able to change the alarm settings.
Alarm function
32 Later versions of the ATG system had the ability to be set to alarm in the event of inconsistencies between tank level measurements and filling data, which would have provided a way of alerting control room staff to an ‘unexpected’ static reading. Had such a modification been made then supervisors may have been made aware of the sticking gauge before an overfill position was reached. A more stringent monitoring scheme could have identified the shortcomings and allowed the site operator to upgrade the ATG system.