ST. LOUIS (AP) - Investigators have found that extremely hot weather was partly to blame for a fire that caused massive explosions last June at a compressed gas facility in St. Louis owned by Praxair Inc.
The U.S. Chemical Safety and Hazard Investigation Board issued a safety bulletin Thursday aimed at avoiding fires at facilities like Praxair's. Among the findings, the CSB found that when exposed to extreme heat and sunlight, propylene cylinders can vent gas through relief valves which can then ignite. The board does not have authority to issue fines or citations.
''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,'' CSB lead investigator Robert Hall said in his report.
The board recommended that compressed gas companies change relief valves on propylene cylinders to avoid too much pressure in them. Propylene is a relatively rarely used natural gas used largely in the welding industry. Hall said about 50,000 cylinders exist. By comparison, there are about 50 million cylinders of propane.
A Praxair spokesman did not return a call seeking comment. The company's own investigation, released in September, determined that a mechanical failure in a gas cylinder led to the fire.
On June 24, 2005, one propylene cylinder stored on asphalt on a day when the temperature reached 97 degrees caught fire _ probably due to static electricity, the CSB report said _ and the blaze spread to propane and acetylene cylinders.
Eventually, more than 8,000 cylinders caught fire, many shooting like missiles into the sky and into the residential neighborhood surrounding the plant. National news programs captured the fireworks-like display live. The cylinders damaged several homes and cars.
No one died immediately after the fire, but 32-year-old Minnie Cooper died 11 days later because her brain was starved of oxygen. Earlier this year, St. Louis Medical Examiner Dr. Michael Graham ruled an ''underlying cause'' of her death was an asthma attack triggered by inhaling smoke and fumes from the incident.
The fire in St. Louis isn't the only one in recent years where leaking propylene containers were to blame. The CSB said another fire occurred at a Praxair facility in Fresno, Calif., a month after the St. Louis fire. Also, similar fires occurred at an Airgas plant in Tulsa, Okla., in 2003, and at Air Liquide facility in Phoenix in 1997.
In the St. Louis fire, CSB investigators believe the asphalt radiated heat from direct sunlight, causing the temperature of the gas inside the cylinders to rise, creating internal pressure. Investigators believe the static electricity that caused the initial fire was created by escaping vapor and liquid.
''The accidents show the need for companies to follow best practices for outdoor cylinder storage and fire protection,'' said Carolyn Merritt, chair of the CSB. ''We hope the industry takes notice with the coming of summer and high ambient temperatures in cylinder storage yards.''
Merritt said some companies, including Praxair, are already replacing relief valves on propylene cylinders with those that do not release gas at prematurely low pressure settings. Praxair has made other changes at cylinder production facilities, the company has said, including installation of secure areas to keep cylinders with flammable gases away from other cylinders.
On Monday, Praxair announced it will leave St. Louis, moving across the Mississippi River to a site in Cahokia, Ill., where it operated a warehouse until 1999. That warehouse has served as the temporary plant since the St. Louis fire.