Explosion
The U.S. Chemical Safety and Hazard Investigation Board investigating the incident found that operators had started-up the raffinate splitter tower (which separates light and heavy gasoline components) of the ISOM unit (which increases the octane rating of gasoline) and begun filling it with hydrocarbon fluid (i.e. gasoline components) without beginning timely discharge of product. The operators started the tower while ignoring open maintenance orders on the tower’s instrumentation system. An alarm meant to warn about the quantity of liquid in the unit was disabled.
Once the lack of draw-down from the tower was recognized, operators opened the discharge valve. This worsened the problem because the hot discharges passed through a heat-exchanger that pre-warmed incoming fluids. The resulting increase in temperature caused the formation of a bubble of vapor at the bottom of the raffinate tower that was already overly full and overheated. The tower burped the vapor bubble and the liquid above the bubble into the overhead relief tube of the tower.
The relief tube was connected to a disposal system for relieved discharges. The particular type of disposal system serving the raffinate tower was a blow-down drum with an atmospheric vent stack rather than an inherently safer and more environmentally sound knock-out tank and flare system.
Because of the overfilling of the raffinate splitter tower and the burp of both vapors and liquids to the undersized blow-down drum with an atmospheric vent stack, a “geyser like” emission of hot flammable vapors and liquids was expelled from the vent stack. The liquids traveled to a trailer 35 meters from the spill site, where most of the victims died. There was a white diesel pick-up truck parked not far away from the blow down stack. The driver got out and left the engine running; when the liquid arrived at the truck it flowed under it and the vapor entered the engine's air intake, causing the engine to rev. A short while after, a spark in the engine set off the explosion.
Aftermath
The CSB report found that BP had failed to heed or implement safety recommendations made before the blast. Among them were:
In 1995, a refinery belonging to Pennzoil suffered a disaster when two storage tanks exploded, engulfing a trailer and killing five workers. The conclusion was that trailers should not be located near hazardous materials. However, BP ignored the warnings, and they believed that because the trailer where most of the deaths happened was empty most of the year, the risk was low.
Between 1994 and 2004 at least eight similar cases occurred in which flammable vapors were emitted by a blow-down drum vent stack. Effective corrective action was not taken at the BP plant. In 1997, BP replaced the 1950’s era blow-down drum / vent stack that served the raffinate splitter tower with an identical system instead of upgrading to recommended alternatives that were safer. In 2002, engineers at the plant proposed replacing the blow-down drum/vent system as part of an environmental improvement initiative but this line item was cut from the budget due to cost pressures.
As a result of the accident, BP said that it would eliminate all blow-down drums/vent stack systems in flammable service. The CSB, meanwhile, recommended to the American Petroleum Institute that guidelines on the location of trailers be made.
Legal action
On February 4, 2008, U.S. District Judge Lee Rosenthal heard arguments regarding BP's offer to plead guilty to a federal environmental crime with a US$50 million fine. At the hearing, blast victims and their relatives objected to the plea, calling the proposed fine "trivial." So far, BP has said it has paid more than US$1.6 billion to compensate victims.The judge gave no timetable on when she would make a final ruling.
Subsequent Incidents
After the March explosion, three other major safety incidents occurred at the plant:
On 28-Jul-2005, a hydrogen gas heat exchanger pipe on the Resid Hydrotreater Unit ruptured, causing a release of hydrogen that erupted into a large fireball. One person received minor injuries. The Chemical Safety Board found that a contractor had accidentally switched a carbon steel pipe elbow with a low alloy steel elbow during maintenance, causing a failure mode known as “High Temperature Hydrogen Attack” (HTHA). The CSB found that BP had not informed the maintenance contractor that the elbows were different, the maintenance contractor had not used any procedure (such as tagging) to ensure that the elbows were re-installed into their original locations.
On August 10, 2005, there was an incident in a Gas-Oil Hydrotreater that resulted in a community order to shelter. This incident occurred when a hole developed in the bottom of a vale that handles high pressure gas and oil.
On January 14, 2008, William Joseph Gracia, 56, a veteran BP operations supervisor, died following head injuries sustained as workers prepared to place in service a water filtration vessel at the refinery's ultracracker unit.
Baker Panel
Following these additional safety incidents, on 17-Aug-2005 the CSB recommended that BP Headquarters commission an independent panel to investigate the safety culture and management systems at BP North America. The panel was led by former US Secretary of State James Baker III. The Baker panel report was released on January 16, 2007. The principal finding was that BP management had not distinguished between “occupational safety” (i.e. slips-trips-and-falls, driving safety, etc.) vs “process safety” (i.e. design for safety, hazard analysis, material verification, equipment maintenance, process upset reporting, etc.). The metrics, incentives, and management systems at BP focused on measuring and managing occupational safety while ignoring process safety. BP confused improving trends in occupational safety statistics for a general improvement in all types of safety.
Additionally the panel created and administered to all five of BP’s North American refineries an employee survey focusing on various aspects of “process safety”. From the survey results they concluded that the Toledo and Texas City plants had the worst process safety culture while the Cherry Point refinery had the best process safety culture. The survey results also showed that managers and white collar workers generally had a more positive view of the process safety culture at their plants when compared with the viewpoint of blue collar operators and maintenance technicians. The director of the Cherry Point refinery was promoted to oversee better implementation of process safety at BP.
CEO Retires
The head of BP (Lord John Browne) retired early amid the various problems plaguing BP in 2005 and 2006 (including the problems at Texas City, the shutdown of the Alaska pipeline, allegations of propane market manipulation, and start-up delays of the Thunderhorse project in the Gulf-of-Mexico).
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