The National Transportation Safety Board has released a preliminary report on the fatal August natural gas pipeline explosion in Lincoln County, but the cause has not yet been determined.
According to the report issued on Tuesday, a 30-inch-diameter natural gas transmission pipeline owned and operated by Enbridge Inc. ruptured on Aug. 1 at 1:23 am.
The rupture released about 66 million cubic feet of natural gas which ignited, killing one person, injuring six others and forced the evacuation of 75 residents from the Indian Camp mobile home park. The fire destroyed five nearby residences, damaged 14 others, and burned about 30 acres of land. The blast threw a 33-foot-long section of the pipeline about 481 feet.
Data provided by Enbridge from its gas control center in Houston, Texas, showed that a rate-of-change gas pressure alarm was received at 1:24 a.m. for Line 15 on the south side of the Danville compressor station. The Danville compressor station operator also received the alarm. The operator told investigators he could see the fire from the compressor station.
Enbridge personnel isolated the affected pipeline segment, which required closing one valve at the Danville compressor station, located 3.5 miles north of the rupture, and manually closing another valve located about 19 miles south of the Danville compressor station. Workers isolated the ruptured pipeline at 2:19 a.m. The natural gas fire was reported under control by emergency responders at 2:56 a.m. and the fire was extinguished at 3:20.
At the accident location, there are three Enbridge pipelines that transport natural gas from Pennsylvania to Mississippi through a common corridor. The ruptured pipe was placed into service in 1957. The pipe had an electric flash-welded seam and was coated with coal tar. The portion of Line 15 at the rupture site consists of 3/8-inch wall thickness steel pipe, with a maximum allowable operating pressure of 936 pounds per square inch, gauge.
When first constructed, gas in Line 15 flowed south-to-north; however, in 2014 Enbridge reversed the gas flow to north-to-south and at the time of the incident it was operating at 925 psi.
In 2011, Enbridge performed an in-line inspection of Line 15 to evaluate pipeline material properties. Additional in-line inspections took place in 2018 and 2019 to evaluate pipeline geometry. Investigators are reviewing and reassessing the in-line inspection data from the area of the rupture.
A week after the accident, the Pipeline and Hazardous Materials Safety Administration issued a corrective action order to Enbridge. Line 15 will be isolated from the adjacent pipelines from Mississippi to Pennsylvania and will operate at or below 80 percent of normal operating pressure, until the terms outlined in the corrective action order are met, and PHMSA approves Line 15 to return to full service.
While on scene, investigators collected sections of the pipeline for metallurgical analysis and testing. They will focus on Enbridge’s inspection and maintenance of the pipeline, metallurgical evaluation of the pipe, and Enbridge’s emergency isolation procedures. Investigators will also review other inspection anomalies, reportable incidents, and a November 2003 rupture on the same line near Owingsville. Parties to the investigation include PHMSA, Enbridge, and Lincoln County Emergency Management.
The family of Lisa Derringer, 58, who died in the explosion, has filed a wrongful death lawsuit against Enbridge, alleging gross negligence.