he deadly natural-gas explosion that rocked three communities near Boston last week occurred as the gas company that serves the area is undergoing a major overhaul of its natural gas lines in the region to replace old cast-iron pipes with new plastic pipe. A similar thing is happening in Ohio.

Columbia Gas of Ohio sought to reassure customers Monday that they are in no danger of an explosion like the one that rocked Boston suburbs last week involving a sister company.

"Our system is operating normally and we have no concerns about the safety of our operations," the company said on its website.

The deadly Boston-area explosion occurred as Columbia Gas of Massachusetts is overhauling its natural gas lines, replacing old cast-iron pipes with new plastic pipe.

Columbia Gas of Ohio is doing the same thing with its lines.

Columbia Gas of Massachusetts and Columbia Gas of Ohio are both owned by NiSource, based in Merrillville, Indiana, but with significant support operations in Columbus.

The explosions last Thursday killed an 18-year-old man and injured several people.

The explosions occurred after too much gas was pumped into a section of pipe owned by Columbia Gas of Massachusetts, according to federal regulators. That caused the combustible fuel to leak into homes.

"The real question for this investigation is why that occurred," Robert Sumwalt, chairman of the National Transportation Safety Board, which is overseeing the investigation, said during a news conference Sunday.

The explosion occurred in an area where Columbia Gas of Massachusetts has been replacing old lines. One of the questions investigators will be studying is whether the construction work was a factor, he said.

As part of the investigation, Sumwalt said the NTSB will be interviewing workers from the NiSource command center in Columbus where gas pressure is monitored throughout the NiSource system. The investigation is expected to take one to two years though preliminary findings could be released sooner.

NiSource, which serves 4 million gas and electric customers in seven states, including Ohio, declined to comment on Monday about possible causes of the explosion.

"The National Transportation Safety Board is investigating the incident. They have the jurisdiction in the case," NiSource spokesman Ken Stammen said.

Columbia Gas of Ohio is in the 10th year of a 25-year plan to replace pipelines throughout the state.

This year, the company is spending $129 million to replace 150 miles of pipeline in Ohio. In central Ohio, Columbia is replacing 29 miles of natural-gas main line and more than 4,000 customer-service lines as part of a $29 million investment.

Overall, Ohio is home to more than 199 pipeline operators that operate more than 56,000 miles of distribution lines and 10,000 miles of transmission lines, according to the Public Utilities Commission of Ohio. The PUCO employs inspectors to make sure the operators followed regulations in terms of designed, construction and operation.

Columbia has had safety issues in the past.

A gas leak and explosion in 2015 destroyed one house and damaged 30 others and caused $9 million in losses in Upper Arlington resulted in state regulators fining Columbia $200,000. Columbia also put in programs meant to make the infrastructure safer.

Still, pipelines are mostly safe, experts say.

"Clearly the chance of a pipeline failing in any particular location is really small, but as we saw in Boston and other places around the country when a failure does occur the consequences can be huge," said Carl Weimer, executive director of Pipeline Safety Trust in Redmond, Washington.

The event in Massachusetts is unusual because of the number of homes and towns involved, said Richard Kuprewicz, president of Accufacts, also in Redmond, which advises companies and governments about pipeline safety.

Right now, it is too early to say exactly what happened and whether it is a company or system problem, he said.

"Everybody take a breath. There are government agencies that do do their job and the NTSB is one of them," he said. "Let's see how they go."

mawilliams@dispatch.com

@BizMarkWilliams