BP’s interim fatal accident investigation report blames a series of failures by BP personnel before and during the start-up of the Isomerisation (ISOM) process unit in the
The Isomerisation (ISOM) unit is used to convert raffinate, a low octane blending feed, into higher octane components for unleaded regular gasoline. The unit has four sections, including a Splitter, which takes raffinate and fractionates it into light and heavy components. The Splitter consists of a surge drum, fired heater reboiler and a fractionating column 164 feet tall.
The investigation team determined the explosion occurred because BP ISOM unit managers and operators greatly overfilled and then overheated the Raffinate Splitter, a tower that is part of the ISOM unit. The fluid level in the tower at the time of the explosion was nearly 20 times higher than it should have been.
The presence of water or nitrogen in the tower at start-up may have also contributed to a sudden increase in pressure that forced a large volume of hydrocarbon liquid and vapour into the adjacent blow down stack, quickly exceeding its capacity. The resulting vapour cloud was ignited by an unknown source.
If ISOM unit managers had properly supervised the start-up or if ISOM unit operators had followed procedures or taken corrective action earlier, the explosion would not have occurred, the investigation team said.
The number of deaths and injuries was greatly increased by the presence of workers in temporary trailers near the blow down stack and the failure to evacuate personnel when it became apparent pressure was building in the ISOM unit and that vapours were being vented to the atmosphere.
The decision to place the trailers near the blow down stack was preceded by hazard reviews that did not recognise the possibility that multiple failures by ISOM unit personnel could result in such a massive flow of fluids and vapours to the blow down stack.
The investigation team also concluded the use of a flare system, instead of a blow down stack, would have reduced the severity of the incident. BP says it will modify or replace all blow down systems which handle heavier-than-air hydrocarbon vapour or light hydrocarbon liquids (gasoline and lighter). In the interim, the company has instituted additional operating requirements to ensure those systems are safely operated until they can be modified or replaced.
“The mistakes made during the start-up of this unit were surprising and deeply disturbing. The result was an extraordinary tragedy we didn’t foresee,” said Ross Pillari, president of BP Products North America.
“We can assure that those who were injured and the families of those who died receive financial support and compensation. Our goal is to provide fair compensation without the need for lawsuits or lengthy court proceedings.”
In response to the report, BP Products will take disciplinary action against both supervisory and hourly employees directly responsible for operation of the Isomerisation Unit on March 22 and 23. These actions, which began yesterday, May 17 will range from warnings to termination of employment. As the investigation continues, others also may be disciplined.
“The failure of ISOM unit managers to provide appropriate leadership and the failure of hourly workers to follow written procedures are among the root causes of this incident. We cannot ignore these failures,” Pillari said.
BP says ISOM unit supervisors did not verify correct procedures were being used by unit operators and were absent from the unit during critical periods. Unit operators failed to sound evacuation alarms, contributing to the severity of the incident.
The report is available to the public and has been posted on the web here.