"To tell you the truth, it's not as easy of a process as you may think that you're going to know exactly what that pipe is and the attributes of that pipe," Sumwalt said. "We have seen in other pipeline explosions where we go and we're told that the pipe is one thing and we find out it's another.
"I don't want to stand here and tell you what we've heard," Sumwalt said. "I want to make sure that, before I release that information, that we actually have a great deal of confidence that's what it is."
On Friday, Peter Knudson, a spokesman for the NTSB, circulated the PHMSA order to reporters covering the Sissonville explosion but would not say if the pipeline data contained in it matched what the NTSB has found so far.
"Our investigators are still in the processes of confirming the age of the segment of pipeline that ruptured," Knudson said. "We expect to include that determination in the preliminary report."
The preliminary report is due out 30 days after the initial incident, or by Jan. 11.
"Given the volume of information that we request from all the entities involved in a major accident," Knudson said, "it is not at all unusual for there to be some pieces of information that will be refined or corrected as the investigation progresses."
Following a September 2010 natural gas transmission pipeline explosion that killed eight people in San Bruno, Calif., pipeline operator Pacific Gas and Electric told the NTSB that the pipe involved was seamless. NTSB investigators later learned that it was made up of six short segments, known as "pups," that were welded together.
In a 153-page report on the San Bruno disaster, the NTSB found that the explosion was caused by a fracture of one of those six pipe sections, and that fabrication of the sections in 1956 "would not have met generally accepted industry quality control and welding standards then in effect, indicating that the standards were either overlooked or ignored."
NTSB investigators found a variety of problems with PG&E's recordkeeping, and with the database used to track pipeline specifications for purposes of determining the integrity of the system and the need for maintenance or replacements.
"There is a very high and very clear expectation from the regulator that the operator knows their lines, knows the risk and appropriately assesses and deals with those risks," Hersman said. "What we see in accidents is that that hasn't happened."
In the interview Wednesday, Hersman said the NTSB is especially concerned about pipelines put into service before 1970, which are "grandfathered in" and don't have to be hydrostatically tested and often can't be examined with in-line integrity devices, known as "pigs." About half the nation's pipelines fall into the pre-1970 category, she said.
"There is a very real safety concern with pipes that are older and have been subject to less-stringent requirements," Hersman said.
The NTSB has recommended eliminating the grandfather provision for hydrostatic testing and requiring that all lines be in-line tested, but those measures were not part of a pipeline safety bill passed by Congress last year and signed into law by President Obama in January.
The PHMSA order contains a few other bits of information, including times for the explosion and the gas flow shutdown, that conflict slightly from what the NTSB previously reported.
The NTSB had said the explosion occurred at 12:41 p.m., and that NiSource crews were not able to manually shut off the flow of gas to the fire until 1:45 p.m. The PHMSA order says the explosion occurred at 12:43 p.m., and that one end of the pipeline was shut off manually at 1:20 p.m. and the other at 1:40 p.m.
NTSB officials have said conflicting times are common in investigations of such incidents, because computers and clocks in various locations aren't synchronized.
The PHMSA report said the pipeline failure "resulted in the release and ignition of an undetermined amount of gas and created two flame plumes." It said 3 homes were destroyed, another seriously damaged and several others damaged.
"We were so fortunate in this accident that there were not fatalities and a number of serious injuries," Hersman said. "From the team that was on the scene, there was a great deal of devastation. We don't want to see this happen again in another community in West Virginia."
Reach Ken Ward Jr. at kw...@wvgazette.com or 304-348-1702.