One Year after Gas Cylinder Fire and Explosions at Praxair St. Louis, CSBIssues Safety Bulletin Focusing on Pressure-Relief Valve Standards and GoodSafety Practices
The following message is from the U.S. Chemical Safety Board, Washington
Washington, DC, June 15, 2006 – The U.S. Chemical Safety and Hazard Investigation Board (CSB) today issued a safety bulletin following the agency’s investigation into the June 24, 2005, fire and explosions that swept through the Praxair Distribution, Inc., gas cylinder filling and distribution center in St. Louis, Missouri. The accident occurred when gas released by a pressure relief valve on a propylene cylinder ignited.
The Safety Bulletin, entitled “Dangers of Propylene Cylinders in High Temperatures: Fire at Praxair St. Louis,” includes key findings, best practices for cylinder storage, and safety recommendations.
In addition, the CSB has released a Safety Video on the incident, which includes a computer animation depicting the gas release, as well as video of the initial release and fire taken by a Praxair security camera. The video features comments by CSB investigators and Chairman Carolyn W. Merritt. This safety video may be viewed and obtained by filling out an online form of request at www.csb.gov.
The bulletin notes that as a result of the fire, dozens of exploding cylinders were launched into the surrounding community and struck nearby homes, buildings, and cars, causing extensive damage and several small fires. Workers and customers quickly evacuated the facility after a worker sounded the alarm at the plant. Fortunately, residents escaped injury from the falling fragments.
CSB investigators noted the accident occurred on a hot summer day with a high temperature of 97 degrees F in St. Louis. At Praxair, cylinders were stored in the open on asphalt, which radiated heat from the direct sunlight, raising the temperatures and pressure of the gas inside the cylinders. At approximately 3:20 p.m., a propylene cylinder pressure relief valve began venting. CSB investigators believe static electricity, created by escaping vapor and liquid, most likely ignited the leaking propylene.
Praxair security camera video shows the initial fire spreading quickly to other cylinders. Exploding cylinders – mostly acetylene – flew up to 800 feet away, damaged property, and started fires in the community. The fire could not be extinguished until most of the flammable gas cylinders were expended. An estimated 8,000 cylinders were destroyed in the fire, which took five hours to control.
The investigation determined that the pressure relief set points, specified in industry standards, are too low for propylene and may allow the gas to begin venting during hot weather – well below the pressures that could damage the cylinders. Not only are the specified set points too low for propylene, the CSB found some valves begin releasing gas even before the pressure reaches the set point. Each time a pressure relief valve opens, its performance deteriorates – making it more likely to vent gas at too low a pressure in the future.
CSB lead investigator Robert Hall said, “The key lesson learned in our investigation is that the combination of high ambient temperatures and relief valves that open at too low a pressure increase the risk of catastrophic fires at these facilities.”
The CSB bulletin lists three similar fires at gas repackaging facilities that were reported to be caused by leaking propylene containers since 1997. Fires occurred at another Praxair facility in Fresno, California just a month after the St. Louis accident; an Airgas facility in Tulsa, Oklahoma; and an Air Liquide facility in Phoenix, Arizona.
Board Chairman Carolyn W. Merritt said, “The fire at Praxair was serious and not the only one that has occurred at compressed gas facilities. The accidents show the need for companies to follow best practices for outdoor cylinder storage and fire protection. We hope the industry takes notice with the coming of summer and high ambient temperatures in cylinder storage yards.”
The CSB Safety Bulletin lists several best practices for cylinder storage at gas repackaging facilities, including fire protection systems to cool cylinders and limit the spreading of fires, adding barriers to contain exploding propylene cylinders within the facility, and gas detection systems that can sound alarms and activate fire mitigation systems.
The Board recommended that the Compressed Gas Association (CGA) revise its standards for propylene relief valves to provide a greater margin of safety and improved reliability.
To see other CSB accident investigations and recommendations, go to: