Gas Line Was Not Marked Before Fatal Dallas Explosion, NTSB Says
A preliminary NTSB report says the natural gas line involved in the fatal Dallas apartment explosion had not been identified and marked before drilling began, as investigators continue examining the cause of the May 28 blast.
(P&GJ) — A natural gas line involved in the May 28 explosion that destroyed a Dallas apartment building had not been identified and marked before drilling began, according to a preliminary report released by the National Transportation Safety Board (NTSB). The explosion and subsequent fire killed three people, injured at least six others and remain under investigation.
According to the NTSB, a third-party contractor working on behalf of Engineering and Consulting Services Southwest LLP was conducting soil sampling near the apartment building before the explosion. The contractor had submitted a Texas 811 excavation notification on May 21, seven days before the incident.
The report states that while some underground utilities had been identified using paint and flags before drilling began, the location of the natural gas line involved in the accident had not been identified and marked. The NTSB did not indicate why the line was unmarked or assign responsibility, noting that the investigation remains ongoing.
Dallas Fire-Rescue responded to a reported natural gas leak at 12:49 p.m. local time on May 28 and notified Atmos Energy of a cut gas line two minutes later. The explosion occurred at approximately 1:15 p.m., destroying the apartment building at 409 E. Ninth St. and prompting the evacuation of eight nearby homes and three apartment buildings.
Atmos Energy crews arrived shortly after the explosion and isolated the leak by hydraulically squeezing the polyethylene natural gas main in two locations. The first squeeze-off was completed at 2:09 p.m., followed by a second at 2:41 p.m., stopping the flow of gas to the damaged area.
The NTSB said the distribution system serving the area included a 4-inch polyethylene natural gas main operating at approximately 38 pounds per square inch gauge (psig), below its maximum operating pressure of 55 psig. A 1¼-inch polyethylene service line connected the main to the apartment building before reducing to a ¾-inch line leading to the building's gas meter. Both the gas main and the ¾-inch section of the service line were installed in 1988.
"Although the locations of some of the assets had been marked by painting and flagging, the location of this gas line had not been identified and marked," the NTSB said in its preliminary report.
The agency cautioned that its investigation is ongoing and that the report does not identify a probable cause.
"All aspects of the accident remain under investigation while the National Transportation Safety Board determines the probable cause with the intent to issue safety recommendations to prevent similar events," the agency said.
Parties participating in the investigation include the Pipeline and Hazardous Materials Safety Administration (PHMSA), the Railroad Commission of Texas, Dallas Fire-Rescue, Atmos Energy, Environmental Consulting Services Ltd. and United States Infrastructure Corporation (USIC Locating Services LLC).
The NTSB will issue a final report after completing its investigation.