NTSB: No Evidence Merrimack Valley Explosions Were Intentionally Caused

LAWRENCE (CBS) – National Transportation Safety Board (NTSB) investigators are working to develop a complete timeline of what led up to Thursday's gas explosions and fires in the Merrimack Valley, but have found no evidence the incident was intentionally caused.

NTSB Chairman Robert Sumwalt said on Saturday that a "pressure increase" was reported at the pipeline controller's console in Columbus, Ohio. The pipeline controller will be interviewed.

"What was their reaction to the pressure increase? That's precisely what we want to find out," Sumwalt said.

Sumwalt said there are a variety of items the investigation looks to uncover, including safety protocols, a timeline of events, and any reports of gas odors in the last three weeks.

The "probable cause" of the incident will not be determined until a later date, Sumwalt said. He added that an "approximate cause" will be known relatively soon.

"We have no evidence at this time that there is anything nefarious, anything suspicious, anything intentional associated with this disaster," Sumwalt said.

Sumwalt said pipeline investigations usually last 12-24 months.

"We want to find out what happened so that other communities don't have to go through the devastation that has occurred in this area," Sumwalt said.