Don Holmstrom, lead CSB investigator for the Texas City investigation, told reporters on June 28 that CSB's evidence indicates several "alarms that should have warned operators of abnormal conditions in the isomerization unit did not go off."
One of the alarms within the isomerization unit did go off at 3:05 a.m. on March 23 about 10 hours before the explosion warning operators of high levels of flammable hydrocarbons in the raffinate splitter tower, Holmstrom said. However, that level indicator then erroneously showed hydrocarbon levels "falling back toward a normal value" from 7:30 a.m. until 1:20 p.m. on March 23, when the explosion within the isomerization unit rocked the refinery.
In reality, the raffinate splitter tower was flooding with flammable liquid to a height of 120 feet or more, Holmstrom said.
A redundant high-level alarm which should have alerted operators anytime hydrocarbon liquid reached a height of 10 feet or more within the raffinate splitter tower did not go off, even as the liquid flooded to more than 12 times that height, according to Holmstrom.
A "high-level alarm" within the blowdown drum the drum is a vertical tank connected to the raffinate splitter did not go off when the drum was flooded with hydrocarbons released from the raffinate splitter tower. That flammable hydrocarbon and liquid shot from the drum's 114-foot-tall vent stack like a geyser on the afternoon of March 23, causing as many as five explosions, according to CSB's investigation.
"Had the alarm sounded properly as the blowdown drum was flooding, it could have alerted operators to the emergency situation," Holmstrom said.
Even though BP officials, when unveiling the company's interim investigation report on May 17, blamed the accident on managers and operators who "greatly overfilled and then overheated the raffinate splitter," BP spokesperson Ronnie Chappell said CSB's latest findings are "absolutely consistent" with the report.
"At the time of the interim report, BP's investigation team was still working to determine if the redundant high- and low-level alarms in the raffinate splitter had functioned as designed," Chappell said. "In preparing its report, the team assumed that the alarms had not worked."
Chappell added that the company stands by its findings as well as its "subsequent personnel decisions." The company announced May 17 that it would "take disciplinary action against both supervisory and hourly employees directly responsible for operation of the isomerization unit March 22 and 23," and Chappell acknowledged that several Texas City refinery employees have been fired.
Chappell said BP's investigation is ongoing and the company expects to publish a final report in late August.
Equipment to Become a Major Focus
Although CSB continues to work on a "multi-layered, complex analysis" of the events that led up to the March 23 refinery explosion, Holmstrom indicated that determining why the aforementioned alarms malfunctioned will be a major focus of the investigation.
"Because of these circumstances, we have extended our field investigation at the BP site and have begun an extensive program of equipment testing within the isom unit," Holmstrom said, adding that CSB officials will begin by testing more than 30 instruments and pieces of equipment, a process that likely will take 4 to 6 weeks.
Ultimately, CSB will analyze the "complex interaction" of all the factors related to the start-up of the isomerization unit, including equipment failures, design flaws, training, "human performance issues" and management oversight, Holmstrom explained.
Among the other factors CSB investigators continue to look at is the location of mobile trailers 100 to 150 feet away from the blowdown drum's vent stack. Workers who were in and around the trailers were killed or injured during the explosions, according to CSB.
Holmstrom, however, said determining the "exact ignition source" of the blasts "is not a principal focus of current work." Vehicles on the ground in the isomerization unit are thought to be among the possible triggers, according to CSB.