(NewsNation) — Senate Majority Leader Chuck Schumer asked National Transportation Safety Board Chair Jennifer Homendy to expand the agency’s investigation into Norfolk Southern to include other railroads as well.

In a letter first reported on by Politico, the Democrat applauded the NTSB’s probe into the Norfolk train that derailed in East Palestine, Ohio, on Feb. 3, and the company’s safety practices. But, Schumer said in his letter, it has become “jarringly evident” in the past five years that the “freight rail industry is in desperate need of a full and comprehensive investigation.”

This being the case, Schumer urged the NTSB to also investigate the safety practices of all Class 1 freight railroads throughout the country, including: BNSF Railway, CSX, Union Pacific, Canadian National, Canadian Pacific and Kansas City Southern.

In an interview with NewsNation, Homendy said she hasn’t yet read the senator’s letter. However, she did say that, excluding any special studies that its research and engineering staff conduct, the NTSB does not investigate unless there is an “accident, precursor accident or incident.”

“I have to see what’s really possible here,” Homendy said.

Lawmakers and residents alike have been asking for answers since the derailment. Residents had to evacuate when responders intentionally burned toxic chemicals in some derailed cars. While officials have said the water and air quality is safe, residents have had lingering health concerns such as headaches.

Questions Schumer said he wants to be addressed by the railroads include: “How have recent deregulatory pushes contributed to these derailments and increase in deaths?”; “What general commonalities can you find among the accidents? How can those be addressed?” and “Does the railroad have a culture of ignoring their own safety standards?”

There have been two other accidents by Norfolk Southern trains since the derailment in East Palestine.

“As we have seen firsthand, the freight rail industry has time and time again dangerously
played fast and loose with the regulations while endangering millions of Americans throughout
the country,” Schumer said.

Freight rail is a “vital lifeline” for local economies, Schumer said, but added that railroads carry hazardous and sometimes toxic materials.

“However, the public, particularly first responders, have few means of understanding what these multi-billion-dollar companies are doing to operate safely — or if they are cutting corners, thus, making it incumbent on the NTSB to assure all Americans that the companies are operating safely, ethically, and efficiently,” Schumer said.

Norfolk Southern isn’t only facing scrutiny from federal agencies. The state of Ohio has also filed a lawsuit against the railroad company to make sure it pays for the cleanup and environmental damage from the derailment.

When it comes to what’s currently happening in the NTSB’s East Palestine investigation, Homendy said this week, the agency is testing some pressure relief valves that were on the vinyl-chloride tank cars.

“We’re looking at the performance of those valves during the fire and during the response,” she said Wednesday. “So that testing hopefully will come back with some information today or tomorrow.”

Meanwhile, Norfolk Southern told NewsNation it is testing East Palestine’s soil for dioxins — a group of hard-to-break-down chemicals that can cause cancer and may result from the burning of vinyl chloride.

“Right out of the gate, there are two problems. First, it’s late. Second, EPA should be doing the testing, not contractors for the rail company,” Judith Enck, a former EPA regional administrator, said.

More than 100 groups, including activists who live in the affected community, are calling for the EPA to take over dioxin testing directly. Right now, it’s reviewing tests done by Norfolk.

“According to scientists, there may be no safe level of dioxin exposure. And that is why it is essential for EPA to do a thorough investigation into whether or not toxins may be found in the communities impacted by this disaster,” Mike Schade, from the organization Toxic-Free Future, said.

The Associated Press contributed to this report.