Soon after the derailment of a Norfolk Southern train in East Palestine, Ohio, a team of researchers began roving the small town in a Nissan van.

It was February, less than three weeks after the disaster, and the van was outfitted with an instrument called a mass spectrometer, which can measure hundreds to thousands of compounds in the air every second.

The decision to vent and burn five train cars’ carcinogenic chemicals in East Palestine, Ohio, in February came under renewed scrutiny Thursday as federal investigators questioned officials in the community still reeling from the aftermath of a toxic train derailment.

The National Transportation Safety Board, or NTSB, on Thursday held the first of two days of investigative hearings in East Palestine, a village of around 4,700 near the Ohio-Pennsylvania border where the Feb. 3 derailment occurred.

The National Transportation Safety Board will start taking sworn testimony Thursday as part of its probe into the toxic train derailment in East Palestine, Ohio.

The agency is holding an investigative hearing on Thursday and Friday in East Palestine, where a Norfolk Southern Railway train carrying toxic chemicals derailed on Feb. 3, resulting in the release of hazardous materials into the air, soil and creeks in the area.

Employees for the Centers for Disease Control and Prevention became sick in March while assessing the health effects of the train derailment in East Palestine, Ohio.

A Norfolk Southern train derailed and subsequently caught fire, spewing vinyl chloride, phosgene, hydrogen chloride, and other gases into the air and water while traveling from Madison, Illinois, to Conway, Pennsylvania, on Feb. 3.

Authorities say seven US health investigators fell ill while probing the impact of the 3 February train derailment in East Palestine, Ohio.

According to the Centers for Disease Control and Prevention (CDC), the investigator's symptoms included nausea and headaches.

Locals in East Palestine have reported similar illnesses.

The train was carrying vinyl chloride and other potentially hazardous substances.

The U.S. Justice Department filed a lawsuit against Norfolk Southern over the major train derailment that occurred in East Palestine, Ohio, last month.

The suit, filed Thursday on behalf of the Environmental Protection Agency, accuses Norfolk Southern Railway Company and Norfolk Southern Corporation of "unlawfully polluting" the country's waterways and violating the Clean Water Act, which prohibits groups from releasing toxic pollutants into waterways without a government permit.

Newly released data shows soil in the Ohio town of East Palestine – scene of a recent catastrophic train crash and chemical spill – contains dioxin levels hundreds of times greater than the exposure threshold above which Environmental Protection Agency (EPA) scientists in 2010 found poses cancer risks.

The EPA at the time proposed lowering the cleanup threshold to reflect the science around the highly toxic chemical, but the Obama administration killed the rules, and the higher federal action threshold remains in place.

The state of Ohio is suing Norfolk Southern over the company’s train derailment in East Palestine last month, Ohio Attorney General Dave Yost announced Tuesday.

“This derailment was entirely avoidable,” Yost said at a press briefing Tuesday, “and I’m concerned that Norfolk Southern may be putting profits for their own company above the health and safety of the cities and communities that they operate in.”

The residents of East Palestine, Ohio, have more than enough to worry about. A train wreck with black fumes of burning chemicals pouring from a tank is frightening enough. The absolute last thing they need is the news media spreading even scarier—but inaccurate—information about the accident.

Yet for weeks, that is precisely what's been going on.

Railroads are a fixture of the American landscape: There are about 140,000 miles of track in the United States. But most people don’t think of the trains running through our towns and cities all that often.

“It was just a means of transportation for moving goods from one point to the other,” Wayne Bable told Vox’s Benji Jones last week in East Palestine, Ohio. “I mean, the trains are every 15 minutes on a regular basis. So it’s just part of life. … After a while, you don’t hear them. We sure hear them now.”