CENTRAL MISSISSIPPI — The National Transportation Safety Board (NTSB) has determined that the probable cause of the 2007 pipeline rupture near Carmichael was the failure of a weld that caused the pipe to fracture along the longitudinal seam weld, a portion of the upstream girth weld and portions of the adjacent pipe joints.
On Nov. 1, 2007, a 12-inch diameter pipeline segment operated by Dixie Pipeline Company was transporting liquid propane at about 1,405 pounds per square inch gauge, when it ruptured, releasing about 431,000 gallons of propane, in a rural area near Carmichael in Central Mississippi. As a result, the propane began to vaporize and form a cloud that expanded over nearby homes. Local emergency responders received calls informing them of the smell of gas and the sighting of white gas. Approximately seven-and-a-half minutes after the rupture, the vapors ignited, creating a fireball.
There were two fatalities and several minor injuries.
The accident pipe was manufactured in 1961 using the low-frequency electric-resistance welding (ERW) process for longitudinal seam welds. The majority of ruptures in ERW pipe involve the longitudinal seams. At the time of the accident, no confirmed in-service pipeline ruptures in girth welds had been reported for the entire pipeline since it was installed. Additionally, segments of the accident pipe had been inspected multiple times since 1998, using in-line inspection tools.
As a result of the investigation, the NTSB issued recommendations to the Pipeline and Hazardous Materials Safety Administration, the Clarke County Board of Supervisors, the American Petroleum Institute and Dixie Pipeline Company on testing of pipeline, public awareness and training and drills for 911 personnel.