BOSTON (WHDH) - Bay State U.S. Sen. Ed Markey is continuing his search for answers about the Merrimack Valley gas disaster after he said the National Transportation Safety Board’s preliminary report raised more questions.

The NTSB’s five-page report released Thursday found that overpressurized natural gas lines were the source of the explosions and fires in Andover, Lawrence and North Andover on Sept. 13, which left one dead and more than a dozen injured.

RELATED: NTSB releases preliminary report on Merrimack Valley gas disaster

Markey says it’s still not clear how Columbia Gas could have allowed the disaster to happen.

“While this report provides some additional context on the timeline of events leading up to and directly following the incident, there are many unanswered questions that this report does not give the answers to the residents of the Merrimack Valley,” Markey said.

The Massachusetts Democrat added that Columbia Gas was not prepared to respond to this kind of catastrophe.

“I have reviewed Columbia Gas’ safety operations and response plans and found that the company was woefully unprepared for a disaster of this magnitude,” he said.

Markey plans on holding congressional hearings in the Merrimack Valley next month in order to get more answers.

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