The National Transportation Safety Board (NTSB) has issued safety recommendations to both the state and Columbia Gas and says that the utility could have easily prevented the natural gas fires and explosions in the Merrimack Valley.

The agency says Columbia Gas' use of work plans prepared by a 'field engineer' — who is not a licensed professional engineer — is partly to blame for the accident.

The NTSB is now urging the state to adopt new safety protocols. The recommendations include a call for Massachusetts to start requiring public utilities to have professional engineers sign off on work plans.

A spokesperson for Columbia Gas said the utility is reviewing the report and will continue to work with the NTSB.

In a statement released Thursday in response to the NTSB report, Columbia Gas’ parent company NiSource said it “has identified, and moved ahead with, new steps to enhance system safety and reliability and to safeguard against over pressurization.”

Those steps, the statement continued, include the installation of over-pressurization protection devices and remote monitoring devices.

Meanwhile, in the city of Lawrence, thousands of families are still waiting to return home. And Dan Rivera, the city’s mayor, says the NTSB asserting the utility could have prevented the accident comes as no surprise.

"That's been clear to me since day one, the NTSB pointing it out just underscores what everybody else believes,” Rivera said.