By Cable, Josh
Occupational Hazards , Vol. 69, No. 5
Time after time, those of us in the safety community read about workplace injuries and fatalities that were completely preventable. "Had Company X just followed basic workplace safety requirements," the investigating agency often concludes, "this accident never would have happened."
Tragically, the March 23, 2005, explosion and fire at BP's Texas City, Texas, refinery--which took the lives of 15 workers, sparked the largest investigation in Chemical Safety and Hazard Investigation Board (CSB) history and created a public relations nightmare for London-based BP PLC--was just such an accident.
With the release of CSB's final investigation report on the root causes of the BP refinery tragedy, as well as with the previous releases of the independent Baker panel report and BP's own investigation report, the safety community now has unprecedented insight into the decisions and actions that precipitated the worst U.S. industrial accident since 1990.
The body of evidence and information available to the safety community--and to the public--is the anatomy of a workplace tragedy that never should have happened. It is the anatomy of a tragedy that, in the words of CSB Chairwoman Carolyn Merritt, was "the inevitable result of a series of actions" by BP.
Technical Cause Not in Dispute
By now, there's little dispute over what happened in the hours leading up to the accident. During a startup of the refinery's isomerization unit, operators pumped flammable liquid hydrocarbon into the raffinate splitter tower without allowing any liquid to drain from the bottom of the tower into storage tanks--which was contrary to startup procedures.
The liquid overflowed into piping off the top of the tower, triggering emergency relief valves to open. The emergency valves channeled liquid hydrocarbon into the blowdown drum at the other end of the isomerization unit.
In the 6 minutes that the emergency relief valves were open, CSB estimates that 51,900 gallons of flammable liquid flowed from the raffinate splitter to the blowdown drum.
The drum filled completely, and, consequently, liquid hydrocarbon spewed from the 113-foot tall blowdown stack like a geyser. Although the eruption only lasted about 1 minute, CSB estimates that the blowdown stack released 7,600 gallons into the atmosphere.
The volatile liquid hydrocarbon evaporated as it fell to the ground and created a large flammable vapor cloud, which spread quickly throughout the area. At 1:20 p.m. on March 23, 2005, the cloud ignited, likely after coming into contact with an idling diesel pickup truck parked about 25 feet from the blowdown drum.
According to BP's modeling and other calculations, the ignition of the vapor cloud created a fireball with a diameter as large as 236 feet. BP estimates that the fireball lasted 6 seconds.
CSB and BP agree that the 15 contract employees killed in the explosion were working in or near mobile trailers located too close to the blowdown drum. Many of the injured also were in or near these trailers, which were used for supporting turnaround work on the nearby ultracracker unit.
The explosion caused heavy damage within the isomerization unit, severely damaging the satellite control room and destroying the catalyst warehouse. The blast damaged or destroyed a number of vehicles and mobile trailers near the isomerization unit.
The explosion also damaged more than 50 large chemical storage tanks--many located more than 250 feet away--and broke windows, cracked masonry walls and damaged doors in surrounding units of the refinery.
Off site, the blast shattered windows in homes and businesses up to three-fourths of a mile away from the isomerization unit.
One Key Mistake?
While BP's final investigation report admits that there was a complex set of "underlying reasons for the behaviors and actions during the incident," the report clearly emphasizes that workers and supervisors caused the accident by deviating from procedures. …