CSB Identifies Immediate Cause of Catastrophic Pressure Vessel Failure

Published May 31, 2017

​The U.S. Chemical Safety Board (CSB) has released an update on its investigation of last month’s catastrophic pressure vessel failure in St. Louis, Mo., that killed four people—one worker and three members of the public—and critically injured another. The fatalities occurred when a steam condensate storage tank, or semi-closed receiver (SCR), launched out of the Loy-Lange Box Company facility and into a nearby laundry facility. The vessel, which weighs nearly 2,000 pounds, was launched more than 400 feet into the air and 500 feet from its starting point, according to the agency. CSB found the immediate cause of the incident to be the sudden mechanical integrity failure of the ring of the bottom of the pressure vessel, which ruptured and separated the bottom of the tank from the rest of the vessel. According to investigators, this failure created unique conditions for a steam explosion so hazardous that the energy released was equivalent to about 350 pounds of TNT.

The CSB team has also identified a history of leaks in the pressure vessel, which was repaired in 2012 when it was discovered that water was leaking from the bottom of the tank. The company replaced a portion of the tank bottom in an “emergency repair.” Years later, on March 31, 2017, employees noticed new leaks in the bottom of the pressure vessel coming from two sections of original material surrounding the section that was replaced in 2012. The steam generation system and pressure vessel ruptured in that same area three days later.

CSB also notes that the City of St. Louis was required to inspect the SCR by its ordinance. However, the city has provided no evidence of inspection.

CSB’s investigation will continue with mechanical analysis and additional document reviews, interviews, research, and analysis. More information on the agency’s investigation is available on its website.