Video cameras on bus record Durham gas explosion
But the report says investigators for Dominion (PSNC) Energy do not yet know what ignited the gas leak or whether utility lines were properly marked for a contractor laying underground fiber cable.
Those questions and more were highlighted in the mandatory report from PSNC to to the Pipeline and Hazardous Materials Safety Administration (PHMSA). The News & Observer obtained a copy of the report after a public records request through the Freedom of Information Act.
The gas explosion leveled one building and cost millions in property damage.
A contractor who called 911 at 9:37 a.m. said, “We hit a gas line.” The building at 115 N. Duke St. exploded at 10:07 a.m.
Gas companies must provide an incident report to the PHMSA within 30 days of a “significant” gas pipe damage. The report is from the gas company’s internal and ongoing investigation of the explosion and states all numbers should be treated as estimates.
The report doesn’t represent findings from investigating organizations like the N.C. State Utilities Commission.
Bill Gillmore, deputy director of the operations divisions for the utilities commission, said in a previous interview it could take months or years for its investigation to be complete.
Here are highlights from the gas company’s 10-page report.
PSNC’s report concludes a “mechanical puncture” caused the gas leak, but does not say the exact time the pipe was damaged.
A mechanical puncture is “typically [caused] by a piece of equipment such as would occur if the pipeline was pierced by directional drilling or a backhoe bucket tooth,” according to PHMSA.
Direction drilling — a common method of drilling for installing utility lines — was listed as the type of excavation at the scene.
The report does not list the contractor, but PS Splicing reported the damage to the gas line through the North Carolina 811 system. Anyone who damages a utility line is required to immediately contact 811 to report the damage and reach out to the utility company.
The 811 system was notified at 9:31 a.m., six minutes before the contractor’s call to 911.
A PSNC “first responder” was notified at 9:36 a.m. by 811. PSNC also received a call from 911 about the gas leak at 9:48 a.m., according to the report.
Someone had called 911 at 9:11 a.m. reporting the smell of gas a block away from the explosion, but firefighters were not able to detect the smell of gas at the reported area. and officials have not said the two incidents were related.
Markings in question
Before underground work begins, a company must call 811 so utilities can be notified and the underground pipes can be marked.
“While PSNC has determined that its gas facilities were located by its contract service provider, the investigation has not yet confirmed that the lines either were or were not marked accurately,” the report said.
A PSNC spokesperson previously told the N&O “we feel incredibly confident that the lines were marked accurately.”
‘Inconsequential’ amount leaked
PSNC did not receive an automatic alert after the gas-line break because pressure in the pipes did not fluctuate from normal operating pressure, according to the report.
A “supervisory control and data acquisitions” system — used, among other things, to measure the pressure within the gas system — was in place and there were two monitoring points within the distribution system. The monitoring points were at larger pipes, two miles “upstream” of the break.
“The volume of gas lost was inconsequential” and “there was not a significant or correlating resultant pressure drops at these points,” according to the report.
The gas was turned off until 11:10 a.m.
The volume of gas that leaked was an estimated 46,000 cubic feet or about half the size of an Olympic pool.
The estimated cost of the gas released? $196.
The PSNC investigation is ongoing and the report states the company still doesn’t know the ignition source “inside of the structure that exploded” nor the precise number of injuries, though its says various media reports list the number to be between 17 and 25 people.
The costs of property damage, repairs and restoration and emergency response are unknown. The damaged buildings are valued at over $100 million, the N&O previously reported.