Massachusetts Sens. Ed Markey and Elizabeth Warren demanded answers at a Senate field hearing about the Sept. 13 gas explosions and fires in Lawrence, Andover and North Andover that killed at least one person and left thousands of residents displaced and without heat and hot water.

The Senate Committee on Commerce, Science and Transportation has oversight of federal safety agencies like the National Transportation and Safety Board and the Pipeline and Hazardous Materials Safety Administration, the agencies now investigating the September disaster.

In his opening remarks, Markey said the disaster, which caused hundreds of businesses to close temporarily, was not “inevitable,” but instead a “preventable” accident that should never have occurred.

Read more: 'Absolute War Zone,' Says Andover Fire Chief After Dozens Of Gas Fires And One Fatality Rock The Merrimack Valley

First to speak before the panel was Lucianny Rondon, sister of 18-year-old Leonel Rondel, who was killed when his car was struck by debris during the fires and explosions.

Speaking through tears, Rondon described her brother as a kind and loving uncle and said her family is devastated.

“Nobody should ever go through what my family has gone through ever again,” Rondon said to a standing ovation from the 200-plus audience.

The presidents of Columbia Gas of Massachusetts — the utility responsible for gas lines in Lawrence, Andover and North Andover — and its parent company, Indiana-based NiSource, were both present and have pledged to answer questions from the Senate panel.

In initial questions, Markey asked NiSource president Joe Hamrock whether he promised to make affected individuals and businesses “100 percent whole.”

“Yes, we will,” Hamrock answered.

“The responsibility for restoration is ours,” he added.

Read more: Transportation Safety Board Says Columbia Gas Could Have Prevented Merrimack Valley Fires

Previous reporting by WGBH News found that agreements between all of Massachusetts’ gas utilities and the state’s Department of Public Utilities appear to protect the utilities from liability for any “non-direct” damages – including displacement and lost business.

In her initial questions, Sen. Elizabeth Warren asked the presidents of each company how much they had been paid the year before.

NiSource president Hamrock said he was paid approximately $5 million; Bryant answered approximately $550,000.

Asked whether their pay had been reduced as a result of the incident, Hamrock suggested his compensation might be lowered; Bryant said he had told Hamrock he should not receive the approximately $300,000 portion of his salary that is an “incentive” bonus, and that he would refuse the bonus if offered.

The Senate panel also asked questions of the NTSB, the federal agency now investigating the incident, and PHMSA, the pipeline safety agency that has regulatory oversight over gas distributors.

Richard Kuprewicz of Accufacts Inc, an engineering consulting firm, testified that federal regulations are notoriously weak and do not require that pipeline work be certified by trained engineers or performed by properly qualified workers.

The NTSB’s recent report noted that Colubmia Gas did not require a certified engineering professional to sign off on the work order that apparently led to over-pressurized gas lines and the subsequent explosions and fires.