07 April 2005 23:44 [Source: ICIS news]
HOUSTON (CNI)--A “geyser-like release” of hydrocarbon vapour and liquid from a vent stack led to the 23 March explosion at the BP refinery explosion that killed 15 people, an official with the US Chemical Safety and Hazard Investigation Board (CSB) said Thursday.
CSB investigation manager Bill Hoyle gave an update of the CSB’s probe of the explosion at the 460,000 bbl/day Texas City refinery’s isomerisation unit, which was used to increase the octane level of gasoline.
Hoyle said the accident occurred during the restarting of process equipment known as the raffinate splitter, which separates hydrocarbons including pentane and hexane, Hoyle said. “We believe that the raffinate splitter developed excess internal pressure, causing one or more pressure relief devices to open. When these devices opened, hydrocarbon liquid and vapour flowed into a vessel known as a blowdown drum. The blowdown drum includes a 100-foot-tall vent stack which goes to the atmosphere.”
Hoyle said the blowdown drum was not able to contain the hydrocarbon release, and it was not connected to a flare system to combust the flammable vapour.
“Instead, there was what witnesses describe as a geyser-like release of hydrocarbon liquid and vapour directly from the stack.” Hoyle said. “The witnesses saw the liquid and vapour fall to the ground. Shortly afterward, the hydrocarbon ignited, and within seconds there was a powerful explosion, which resulted in deaths and injuries among personnel in nearby trailers and elsewhere.”
Hoyle said the exact ignition source for the hydrocarbon remains unknown, as does the cause of the excess pressure in the raffinate splitter.
When the CSB team entered the explosion site 1 April, it found the remnants of about 30 vehicles near the vent stack, including some within 25 yards.
Hoyle said the CSB team has conducted 75 detailed interviews with eyewitnesses. “We expect the field phase of our investigation to continue for at least several more weeks,” he said.
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