Washington, DC, March 4, 2005 - The U.S. Chemical Safety and Hazard Investigation Board (CSB) is conducting extensive physical testing of equipment and materials to help determine the causes of the December 3, 2004, tank explosion and fire at the Marcus Oil and Chemical facility in southwest Houston.
The Marcus facility produces polyethylene wax using petrochemical waste products; most of the facility has not operated since the December 3 explosion, which was felt around the Houston area and caused damage to nearby properties. According to CSB lead investigator John Vorderbrueggen, the plant has five identically sized large pressure vessels that were bought as surplus in the early 1990s and then were modified for use at the facility. One of these vessels, Tank No. 7, failed violently on the evening of December 3, initiating the fire and other blasts.
CSB investigators have cut samples of carbon steel from the ruined shell of Tank No. 7, which prior to the accident was approximately 54 feet long, 12 feet in diameter, and weighed 51,000 pounds. Before the accident, the tank had been modified through an undocumented welding operation performed at the Marcus plant site. The samples are now being subjected to metallurgical analysis to determine the tank failure mode. None of the five tanks had safety valves to release excess internal pressure.
"Texas has no statewide pressure vessel code, and therefore none of five pressure vessels at the site was required to conform to accepted industry standards," Vorderbrueggen said. "The American Society of Mechanical Engineers (ASME) Boiler and Pressure Vessel Code requires pressure vessels to meet stringent design, fabrication, and testing requirements before use. In addition the code requires the installation of pressure relief valves to protect vessels from over-pressurization and possible rupture. Tank modifications involving welding must be performed by qualified and certified welders using specific materials and techniques. Thirty-eight states have adopted the ASME code into their state regulations. While the state of Texas has not the adopted the pressure vessel code, adherence to the ASME Code principles is essential to the safe operation of pressure vessels, such as the one that exploded."
Samples of wax raw material were collected and are being analyzed to determine their combustibility and other hazard characteristics. In addition, the CSB is testing the plant's nitrogen-generating system, which was used to pressurize Tank No. 7. The testing will determine whether the nitrogen supply was at the intended pressure, and also whether the nitrogen was pure enough to prevent combustion of the heated organic materials inside the tank.
"When the battery of tests is completed, we will all have a far better picture of what went wrong the night of December 3. We expect to know the source of the pressure that ruptured what was likely a weakened vessel," said Board member John Bresland, who accompanied the CSB investigative team and who briefed Houston city officials on the status of the investigation yesterday. "The CSB's mission is to determine the root causes of this accident and develop safety recommendations that will prevent similar accidents at other facilities."
Mr. Bresland said the Board would be also be issuing specific recommendations to Marcus. However, he noted, the CSB does not assess the overall safety of chemical plants, leaving that to appropriate regulatory agencies. "The issue is larger than a single facility," Bresland commented, saying that the Board would likely make a decision within the next two months on whether to hold a public hearing in Houston on the safety questions raised by the accident.
The CSB is an independent federal agency charged with investigating industrial chemical accidents. The agency's board members are appointed by the president and confirmed by the Senate. CSB investigations look into all aspects of chemical accidents, including physical causes such as equipment failure as well as inadequacies in safety management systems.
The Board does not issue citations or fines but does make safety recommendations to plants, industry organizations, labor groups, and regulatory agencies such as OSHA and EPA. Further information about the CSB is available from www.csb.gov. For more information, contact Daniel Horowitz at 202-261-7613 / 202-441-6074 (cell) or Sandy Gilmour at 202-251-5496 (cell).