The corporate parent of the Massachusetts natural gas utility that's the focus of an investigation into explosions and fires that killed one person and injured about 25 others had links to three previous gas line blasts, a review of federal and state records and court filings shows.

The links emerged as Columbia Gas of Massachusetts scrambled to provide assistance and information to residents of Lawrence, North Andover and other Merrimack Valley communities after Thursday's tragedy.

The history of other accidents also came as the National Transportation Safety Board launched an investigation that showed Columbia Gas pipes in the area of the explosions had been over-pressurized.

Normally, gas would flow into residences at a rate of a ½-pound per square inch, NTSB Chairman Robert Sumwalt said Sunday in Massachusetts.

"We believe the gas did indeed flow into homes at significantly greater flow rates and pressure. The real question for this investigation is to answer why this occurred," Sumwalt said.

A pressure increase in the disaster area also had been indicated on the pipeline controller's console in Columbus, Ohio, around the time of the disaster, Sumwalt said Saturday.

Columbia Gas of Massachusetts is the business name of Bay State Gas Company, according to a written summary of testimony that Stephen Bryant, the utility's president and chief operating officer, provided in April for a rate hike request submitted to the Massachusetts Department of Public Utilities.

Incorporated in 1974, the company is one of seven natural gas distribution companies that are subsidiaries of NiSource, a publicly traded holding company based in Merrillville, Indiana.

NiSource shares plunged in Friday trading, closing 11.7 percent lower at $24.79, one day after reaching a 52-week high. The stock was up nearly 3.7 percent in mid-day trading Monday.

Columbia Gas distributes natural gas to roughly 321,000 residential, commercial and industrial customers in three Massachusetts areas centered in Lawrence, Springfield and Brockton, according to Bryant.

NiSource’s combined utility operations serve approximately 3.9 million customers in seven states and operate roughly 60,000 miles of distribution pipelines.

The Massachusetts tragedy has renewed public focus on the safety of natural gas pipelines and the companies that own and maintain them. Through its subsidiaries, NiSource had links to at least three gas line explosions in three states during the last six years, including another blast in Massachusetts.

Springfield, Massachusetts, explosion

In November 2012, a Columbia Gas of Massachusetts service line explosion injured 21 and destroyed a building that housed the Scores strip club in Springfield, west of Boston. The blast heavily damaged roughly a dozen nearby buildings and blew out windows in others.

NiSource said in a Securities and Exchange Commission filing that the gas service line was pierced, and an explosion occurred, "while Columbia of Massachusetts was investigating the source of an odor of gas."

Columbia Gas spokeswoman Andrea Luppi in 2014 told The Republican, a Springfield newspaper, that the company had paid millions of dollars to settle 84 percent of the damage claims filed by 832 individuals and companies.

Luppi acknowledged the Springfield tragedy was the costliest incident in the company’s history at that time, the news organization reported.

The settlements included a $650,000 agreement to repay the city for property damage and other expenses. The utility also agreed to provide a $200,000 grant to the city for planning and urban renewal efforts.

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However, some Springfield residents and businesses that suffered from damage caused by the explosion sued Columbia Gas.

Julio and Evelyn Edwards, a local radio station and a church organization filed a 2015 federal lawsuit that alleged the Edwards family members were left homeless, while the businesses were unable to operate for months. They sought $1.5 million in collective damages.

Massachusetts U.S. District Court Judge Mark Mastroianni dismissed the case in 2016 on legal technicalities. The plaintiffs mistakenly identified the utility in the lawsuit as Columbia Gas of Massachusetts.

The proper legal entity is Bay State Gas Company (doing business as) Columbia Gas of Massachusetts, the utility said. Additionally, the federal court lacked jurisdiction because the company and plaintiffs all were based in Massachusetts.

Russell Shaddock, the owner of the building that had housed the Scores strip club, filed a separate 2014 lawsuit in Hampden Superior Court seeking $1 million in damages from Columbia Gas. The Republican reported that a spokeswoman for the utility said Shaddock had not accepted settlements offered by the company.

Shaddock did not respond to a telephone message Friday seeking comment about the case.

West Virginia pipeline blast

In December 2012, an interstate natural gas pipeline operated by Columbia Gas Transmission, another NiSource subsidiary at that time, exploded in Sissonville, West Virginia.

Escaping high-pressure gas from the 20-inch pipeline sparked a fire that destroyed three homes in the sparsely populated area, according to a National Transportation Safety Board report. The explosion also propelled a 20-foot section of the pipe more than 40 feet from its original location, the report said.

Two Columbia Gas operations personnel who were repairing a leak on a production pipeline about 4.75 miles from the accident location stated that "they could hear the roar from the releasing gas," the report added.

The ruptured pipe was part of a pipeline segment that was installed in 1967, the report said.

The NTSB concluded that the probable cause of the rupture was external corrosion of the pipe wall due to deteriorated coating. Additionally, the report cited the utility company's failure to detect the corrosion "because the pipeline was not inspected or tested after 1988."

Ohio Pipeline Explosion

A natural gas release from an "improperly abandoned" service line was responsible for a March 2015 explosion and fire, the Public Utilities Commission of Ohio concluded in a report on the Upper Arlington disaster that caused $9 million in structural damage.

The report focused on the actions of Columbia Gas of Ohio, a NiSource subsidiary.

The state regulator's staff concluded that the gas line was installed at a home on Sunningdale Way in 1960 and was taken out of service between 1985 and 1997. However, the line was never disconnected from the gas main and was not plugged or sealed, the report said.

"Columbia Gas did not follow their operation and maintenance procedure" with regard to the gas line, the regulator concluded.

The explosion occurred after Columbus Water Department employees went to the home to disconnect water service in preparation for planned plumbing work on a water leak. The workers mistakenly opened the gas valve box while doing the work, the report said.

As a result, gas flowed through the abandoned gas line, into the home, and around the neighborhood. A U.S. Postal Service employee reported a "strong smell of natural gas" while delivering mail on March 21.

However, the warning came too late to avoid the explosion and fire.

In 2016, the Public Utilities Commission of Ohio approved an agreement that required Columbia Gas of Ohio to pay a $200,000 fine, improve its record keeping and enhance safety outreach in the utility's service territory.

Rate hike application

Separately, Columbia Gas is pursuing a gas rate hike request the utility filed in April with the Massachusetts Department of Public Utilities. The company's originally proposed $44.5 million distribution rate increase was reduced to $33.2 million in a tentative settlement agreement filed on Sept. 5.

Approval from the state regulator is required before any rate hikes can be imposed on utility customers.

Follow USA TODAY reporter Kevin McCoy on Twitter: @kmccoynyc