As officials continue investigating the cause of a fatal explosion earlier this month on the Texas Eastern Transmission (Tetco) system in Kentucky, parent company Enbridge Inc. must keep all three pipelines at the site of the incident shut down until further notice, regulators said Thursday.

The Pipeline and Hazardous Materials Safety Administration issued a corrective action order requiring that Enbridge continue to keep Line 15, where the explosion occurred, and the nearby Lines 10 and 25 offline until further notice.

The Aug. 1 explosion, which occurred in the early morning hours on the 30-inch diameter Line 15 near Danville, KY, killed one person and hospitalized six others. According to PHMSA, the blaze from the incident destroyed multiple structures and burned vegetation over roughly 30 acres of land. The pipeline failure released an estimated 66 MMcf of natural gas.

Line 15, a 775-mile bi-directional pipe that runs from Pennsylvania to Mississippi, is one of three pipelines running through the same corridor where the failure occurred; it runs between Tetco’s 30-inch diameter Line 10 and the 30/36-inch diameter Line 25. Line 15 was constructed beginning in 1942, according to PHMSA.

All three lines have been shut down since the incident, limiting north-to-south flows through Tetco’s Danville, KY, compressor station to zero.

“Lines 10 and 25 run on either side of Line 15 in the immediate vicinity of the failure site,” PHMSA said. “At this time, the possibility of damages to Line 10 and 25 from the concussive force of the failure or of thermal damage from the resulting fire cannot be ruled out.”

PHMSA said the explosion ejected a roughly 30-foot long section of Line 15, which landed about 460 feet from the failure site. The blast also left a 50-foot long, 35-foot wide and 13-foot deep crater.

“The affected segment contains an as-yet-to-be-determined amount of A.O. Smith-manufactured pipe of similar vintage and type to the pipe involved in the failure,” PHMSA said. “At this time, the actual cause of the failure has not been determined.”

The section of pipe where the failure originated is under the control of the National Transportation and Safety Board, which is now leading the investigation.

Enbridge said Friday that it is “working diligently to comply with the requirements identified by the PHMSA, and to return to service” Line 10 and 25, which “were taken out of service as a precautionary safety measure.”

“Enbridge takes these issues very seriously. We will address all the site-specific concerns identified by PHMSA and will be undertaking rigorous inspections on the pipelines in compliance” with Thursday’s order “before returning the two pipelines to service.

“These pipelines will not be returned to service until we satisfy regulatory requirements and it is safe to do so. We have no timelines on when that will occur,” management said.

In the hours after the blast, natural gas futures prices spiked briefly as the market reacted to the potential disruption to supplies flowing north-to-south out of the Marcellus and Utica shale region. Late last week, Genscape Inc. analysts estimated that in the immediate aftermath of the incident, flows through the area dropped by about 1.6 Bcf/d day/day.