What to Know A Columbia Gas employee repeatedly raised alarms about policy changes and staff changes, warning the changes could lead to catastrophe.

“We didn’t have enough people to respond and to provide a safe, reliable natural gas," the employee said.

“I think it is a resource issue,” the employee said. “In particular, in the Lawrence location, the resources were minimal."

A 42-year Columbia Gas employee repeatedly raised alarms about policy changes and staff changes to his critical gas-pressure monitoring department, warning the changes could lead to catastrophe.

Bart Maderios gave an exclusive interview to the NBC10 Boston Investigators in which he said he warned Columbia Gas’s general manager, Frank Davis, and another senior employee, Dana Argo, that what he described as cutting corners would make work on gas lines less safe.

“I had left months before, yes, and that’s probably my biggest problem,” said Maderios. “If I was there we wouldn’t be having this conversation today because that would have been prevented.”

Maderios was manager of the meters and regulation department, which monitored gas pressure and the underground sensor system in the Lawrence area.

He retired from Columbia Gas three months before the Merrimack Valley explosions, which federal officials say were caused by over-pressurized gas lines.

And before he left, he said he warned Davis and others “that they were going to miss something. When you deplete the resources somebody’s got to cut corners.”

Maderios said company officials also cut his department – the one responsible for monitoring the gas pressure–from four employees down to one.

“I told them this is not a good idea,” he said. “We didn’t have enough people to respond and to provide a safe, reliable natural gas.”

And another significant change: not requiring experienced technicians to be present on work sites.

“I think it is a resource issue,” he said. “In particular, in the Lawrence location the resources were minimal. They didn’t have enough resources and I couldn’t provide a technician to go babysit a construction job.”

An on-site technician from his department would monitor the gas pressure in the lines during work, while directly communicating with the work crew.

According to a report the National Transportation Safety Board released on its investigation of the explosions, “Columbia Gas offered no explanation as to why this procedure was phased out.”

The NTSB report focused fault for missing the pressure buildup that led to the explosion and fires on a field engineer with “limited knowledge about the importance” of pressure-sensing lines.

An NTSB investigator testified at a field hearing, “We know that not all of Columbia Gas internal departments were required to review all the plans, nor were they required to be approved by a professional engineer.”

The report concluded the field engineers did not share their plans with other departments because they “did not believe they needed to.”

One of those departments not consulted was Maderios’ former department, meters and regulation. He said that wouldn’t have happened on his watch.

“Before I retired I would sit down with engineers and construction,” he said. “We would review the procedures…the drawings and make sure we had everything in place.”

And without those meetings, he said the crews wouldn’t know crucial details about the lines they were working on.

“This is where experienced people would say, whether it be the construction crew that just replaced those lines a few years ago or M & R, would have said, ‘Yeah those control lines are over in that other main,’” he said.

Someone from his former department monitoring the job on site and familiar with the local details could have prevented the pressure buildup to begin with.

“A qualified, experienced supervisor would have made the decision to shut one or two stations off immediately,” Maderios said. “They could have immediately ceased the procedure to prevent that from taking place. Why they didn’t do that I don’t know.”

And the right technicians could have had the experience and confidence to order the pressure regulator and valves shut immediately, something Mederios and the NTSB report said did not happen.

“There is no way that valve could not have been left on for hours,” he said.

Indeed, according to the NTSB report, the explosions started just after 4 p.m., and the valves were not shut off until nearly 7:30 p.m.

Maderios praised his former co-workers and said it was difficult to criticize the lead up to the explosions. He trained a lot of the first responders who ran to help that day on what to do in that very situation.

But he said he was perplexed senior leadership ignored his warnings, and beside himself that they came true.

“My job at Columbia Gas was to do this work and make sure this didn’t happen, and I did it proudly,” he said. “And I am proud I did it for 42 years without incident. And two months after I leave, to have it happen is just unfathomable. I can’t come to grips with it. I really can’t.”

Columbia Gas declined an interview, saying the ongoing NTSB investigation prohibits them from commenting.

As for technicians on site, they said in a written statement, “We value the NTSB’s perspective on this issue. We are still reviewing the facts and circumstances that may have led to this tragic event, including practices in Massachusetts, both at present and in the recent past.”

Along with the NTSB probe, Columbia gas also faces a criminal investigation led by the U.S. attorney’s office.

Explosions tore through dozens of homes on Sept. 13, leaving thousands in Andover, Lawrence and North Andover homeless and without electricity and gas. Hundreds of people are still out of their homes, according to the latest update from Columbia Gas.