The Chemical Safety and Hazard Investigation Board (CSB) today called on the oil industry to eliminate the type of atmospheric vent that caused a release of flammable hydrocarbons at BP's Texas City, Texas, refinery on March 23, 2005, leading to explosions and fires that killed 15 workers and injured 180 others.
After a unanimous 5-0 vote, CSB issued a call to the American Petroleum Institute (API) – a leading oil industry trade association that promulgates widely used safety practices – to strengthen its existing guidance on pressure relieving and de-pressuring systems to include warnings against using blowdown drums similar to those found in Texas City. The guidance, CSB Chairman Carolyn Merritt explained at news conference earlier today in Houston, should "urge the use of inherently safer flare systems and ensure companies plan effectively for large-scale flammable liquid releases from process equipment."
"Unfortunately, the weaknesses in design, equipment, programs and safety investment that were identified in Texas City are not unique either to that refinery or to BP," Merritt said today. "Federal regulators and the industry itself should take prompt action to make sure that similar unsafe conditions do not exist elsewhere. Taken as a package, the new CSB safety recommendations we issued today will provide for effective guidance, outreach and regulatory enforcement to reduce the risk of similar tragedies in the future."
CSB today also voted to urge OSHA to establish a national emphasis program promoting the elimination of unsafe blowdown systems in favor of safer alternatives such as flare systems. According to CSB's recommendations, OSHA should emphasize the need for companies to conduct accurate relief valve studies and use appropriate equipment for containing liquid releases.
CSB: Eight Previous Vapor Releases from Blowdown Drum Documented
The March 23, 2005, accident at BP's Texas City refinery occurred during the startup of the refinery's octane-boosting isomerization (ISOM) unit, when a distillation tower and attached blowdown drum were overfilled with highly flammable liquid hydrocarbons.
Because the blowdown drum vented directly to the atmosphere, there was a geyser-like release of highly flammable liquid and vapor onto the grounds of the refinery, causing a series of explosions and fires that killed workers in and around nearby trailers.
CSB lead investigator Don Holmstrom, at today's press conference, asserted that the ISOM unit blowdown drum had a number of safety problems.
"This drum simply wasn't large enough to hold all the liquid released from the distillation tower if it flooded," Holmstrom said. "Not only could the blowdown drum not hold enough liquid, but it could not assure safe dispersion of flammable vapors through the vent stack."
Holmstrom added that safe dispersion of flammable vapors would require a high exit velocity that could never be guaranteed when handling multiple discharges through a complex piping system.
That design weakness resulted in unsafe conditions in Texas City prior to the March 23, 2005, accident, Holmstrom asserted.
Holmstrom today said that CSB has documented eight previous releases of vapor from the same blowdown drum from 1994 to 2004. In six cases, dangerous flammable vapor clouds formed at ground level but did not ignite; in two other cases, the blowdown stack caught fire, Holmstrom said.
Prior to the 2005 accident, BP operated 17 blowdown drums for disposal of flammable materials at its five U.S. refineries, according to CSB. BP has since pledged to eliminate all the drums and use safer alternatives, such as flare systems.
CSB Found "Important Gaps" in API Guidance
According to CSB, a properly designed flare system includes an adequately sized vessel for containing liquids and a stack with a flame for safely burning flammable vapors, preventing an uncontrolled fire or explosion near personnel. Flares are the most commonly used disposal system for flammable releases in refineries.
Holmstrom noted that in 1992, OSHA cited the Texas City refinery – then owned by Amoco Corp. – for operating an unsafe blowdown drum. However, Amoco succeeded in having the citation and fine withdrawn, asserting that the drum complied with accepted industry standards embodied in API Recommended Practice 521 (Guide for Pressure Relieving and De-Pressuring Systems).
The CSB recommendation announced today is aimed at strengthening the guidance document so it will explicitly warn against such unsafe blowdown systems, Holmstrom said.
"CSB investigators reviewed API Recommended Practice 521 and found that it has important gaps," Holmstrom said. "It does not consider liquid over-filling of a vessel as a potential hazard. It does not provide adequate guidance for sizing disposal drums. Finally, it does not provide assurance that all flammable vapors released through atmospheric vents will be safely dispersed in air, avoiding the danger of explosion."
- Josh Cable