CSB reveals likely cause of Valero refinery fire

Tag : Fireproofing Board

Nick Snow
Washington Editor
WASHINGTON, DC, July 10 -- The Feb. 16, 2007, fire at Valero Energy Corp.' McKee Refineryin Sunray, Tex., likely was caused by water that leaked through avalve, froze, and cracked an out-of-service section of piping,reported the US Chemical Safety Board July 9.
The refinery did not have an adequate program to identify andprotect from freezing out-of-service or infrequently used piping,CSB said.
CSB said the fire occurred in the refinery's deasphalting unit,which uses high-pressure propane as a solvent to separate gas oilfrom asphalt. The propane leaked from an ice-damaged piping elbowbelieved to have been out of service since the early 1990s whenUltramar Diamond Shamrock Corp. owned the refinery.
The piping crack released high-pressure liquid propane thatignited, causing a massive fire, which injured four workers andforced Valero to evacuate the refinery and shut it down for 2months ( OGJ Online, Feb. 21, 2007 ).
Ultramar Diamond Shamrock had not identified hazards that couldarise from the dead-leg, had not removed the piping, isolated itfrom the process with blinds, or protected it against freezingtemperatures. Nor had officials at the McKee plant applied Valero'spolicies on emergency isolation valves to control its valves, CSBsaid.
CSB has asked the American Petroleum Institute to develop a newrecommended practice to protect refinery equipment from freezingand to improve existing practices related to fireproofing,emergency isolation valves, and water deluge systems. It alsocalled on Valero to improve freeze protection, fireproofing, hazardanalysis, and emergency isolation procedures at its 17 NorthAmerican refineries.
Mike Mayo, Valero's corporate safety director, said the independentrefiner-marketer already has implemented safety measures throughoutits system, including the creation of a corporate process safetymanagement and reliability department.
Dead leg hazard
Refinery employees were not aware that a metal object had wedgedunder a manual valve's gate above the piping elbow, allowing liquidto flow through the valve. Piping above that point contained liquidpropane at high pressure and small amounts of water were entrainedin the propane, CSB investigators said.
"The elbow was part of a 'dead-leg' formed when the piping wastaken out of service. It was not intended to have any flow ofliquid through it.
High-pressure liquid propane flowed through the leaking valve andwas released through the fractured elbow, escaping from the pipe atan initial rate of 4,500 lb/min. It quickly created a hugeflammable vapor cloud that drifted toward a boiler house where itcontacted an ignition source, the agency said.
Plant employees were not able to shut off the supply of fuel to thefire once it started because Valero's procedures requiringinstallation of remotely operable shutoff valves had not beenimplemented, Holmstrom said. "Such valves are especially criticalin high-pressure service to prevent large inventories of flammablematerial inside process equipment from contributing to a fire," henoted.
Pipe bridge collapsed
The growing fire caused a pipe flange on a large propane-filledextractor tower to fail, igniting a powerful jet fire that wasaimed directly at a major pipe bridge carrying liquid productsthroughout the refinery, according to the CSB report. The pipebridge's supports, which were not fireproofed, collapsed, severingprocess pipes essential to the refinery's operation, it said.
"Valero and industry standards require fireproofing of structuralsteel supports up to a maximum of 50 ft from possible fuel sources.The collapse of a nonfireproofed bridge 77 ft away from the sourceof the jet fire indicates that industry practices need to berevised," Holmstrom said.
The fire also caused an estimated 5,300 lb of toxic chlorine to bereleased from three cylinders stored 100 ft away, CSB report said.The chlorine, which was used to disinfect cooling water, could haveposed a serious threat to emergency response teams had they notalready been evacuated.
In addition, the fire threatened a large spherical tank containingup to 151,000 gal of highly flammable liquid butane, investigatorssaid. Valves controlling a water deluge system designed to cool thesphere became inaccessible to operators and could not be opened asa result of the growing fire, they said.
"Refineries should minimize the presence of hazardous substancesnear units where they may be exposed to fire hazards and shouldensure that emergency systems remain operable if a disasterstrikes," Bresland said.
Actions already taken
Mayo said Valero has replaced the McKee plant's damaged propanedeasphalting unit with a redesigned model that has remotelyoperable shutoff valves and other upgraded control systems designedto reduce the risks of such incidents.
The company is reevaluating the fireproofing of pipe racks andother structures at its refineries, Valero's safety director said,and by yearend will have completed a switch from chlorine to asafer bleach solution to treat cooling water.
Contact Nick Snow at nicks@pennwell.com.