February 4, 2010: On a 2-1 vote, the U.S. Chemical Safety Board tonight approved urgent safety recommendations on gas purging safety at a public meeting in Raleigh, North Carolina following extensive testimony and public comment. The draft recommendations, which were approved as presented by the staff without amendment, urged the National Fire Protection Association (NFPA), American Gas Association (AGA), and the International Code Council (ICC) to strengthen the national fuel gas code provisions on purging.
In preliminary findings, CSB investigators determined that the catastrophic ConAgra explosion on June 4, 2009 resulted from the accumulation of significant amounts of natural gas that had been purged indoors from a new 120-foot length of pipe during the startup of a new water heater in the plant that made Slim Jims, a popular beef-jerky product. During pipe purging, workers feed pressurized gas into a pipe in order to displace air or other gases so that only pure fuel gas remains in the piping when it is connected to an appliance such as a water heater or boiler.
CSB investigations supervisor Donald Holmstrom said his team made the recommendations to the board during the course of the ConAgra investigation after discovering gaps in the fuel gas codes. “Purging flammable gases into building interiors is a recipe for disaster. At ConAgra, we determined the accident would not have happened had the gas been vented safely outdoors through a hose or pipe.” Mr. Holmstrom noted that since the June 2009 accident, ConAgra has instituted strict policies on purging, requiring it be done to safe outdoor locations.
As proposed, the CSB recommendations would urge the NFPA and the American Gas Association (AGA), enact tentative interim and then permanent changes to the National Fuel Gas Code. These would require that purged gases shall be vented “to a safe location outdoors, away from personnel and ignition sources.” In cases where outdoor venting is not possible, companies would be required to seek a variance from local officials before purging gas indoors, including approval of a risk evaluation and hazard control plan. The recommendation would also require the use of combustible gas detectors to continuously monitor gas concentrations; the training of personnel about the problems of odor fade and odor fatigue; and warnings against the use of odor alone for detecting releases of fuel gases.
The CSB issued a safety bulletin in October 2009 entitled “Dangers of Purging Gas Piping into Buildings.” The bulletin’s key lesson is: “Purging new or existing gas piping into a building can be highly hazardous due to the possible accumulation of gas … and the associated danger of fire and explosion.” It notes that large numbers of workers are at risk, including plumbers, gas installers, maintenance workers, contract supervisors, and industrial facility managers.
Mr. Holmstrom said, “The CSB has examined several other similar accidents in which gas was purged indoors and not detected. We have determined that workers cannot rely on their sense of smell to warn them of danger, in part because people become desensitized to the odorant added to natural gas and propane. Gas detectors must be used.”
Other incidents examined by the CSB include: a 1999 explosion at a Ford power plant in Dearborn, Michigan, killing six, injuring 38, and causing a $1 billion property loss; a 2008 explosion at a Hilton Hotel under construction in San Diego, California that injured fourteen people; a 2005 school explosion in Porterville, California, burning two plumbers; and an explosion at a hotel in Cheyenne, Wyoming, in 2007 severely burning two plumbers.