(NewsNation) — Transporting hazardous material via railway is both common and generally considered safe, but the practice has come into question after a Norfolk Southern train derailed last month in Ohio and toxic chemicals were released in the nearby area.

Officials have combed through rail safety practices and accident rates after the Feb. 3 derailment of a Norfolk Southern train in East Palestine.

Oversight of hazmat cargo is multifaceted, but still, some politicians would like to be more scrupulous.

Why do trains carry hazardous materials?

Chemicals that make up many of the everyday products widely used across the country are often shipped on rail transportation. Those chemicals include chlorine to purify water and the potassium found in fertilizers.

In the United States, rail is considered the safest method of long-distance chemical transportation on land, according to the U.S. Department of Transportation (DOT).

Railways are also considered common carriers, meaning they’re required to provide “transportation or service on reasonable request,” according to the Federal Register. That statutory requirement bars railroads from refusing transportation services on the basis that it would be inconvenient or unprofitable.

To that end, railroads typically don’t own the tank cars they transport. Those are instead purchased and maintained by shippers or equipment leasing companies, according to the Association of American Railroads (AAR).

Still, freight railroads have invested billions of dollars annually into the infrastructure and development of new technologies to keep shipments running safe and smoothly.

Is it safe?

The DOT divides classifications of hazardous material by varying levels of flammability and toxicity.

Ordinarily, more than 99.9% of all hazmat moved by rail reaches its destination without a release caused by a train accident, according to the AAR.

Hazmat accident rates dropped by 55% between 2012 and 2021, partially because of existing regulations and ongoing improvements to training and safety standards, according to the AAR.

Accidents do happen, however. In 2022 there were 365 reported incidents involving transporting hazardous material on rail, according to the DOT.

That’s far fewer than the number of hazardous material incidents reported on the highway (23,189), according to the same DOT data.

How much do they carry?

U.S. railroads are responsible for moving more than two million carloads of hazardous materials annually, including 2.2 million carloads in 2021, the most recent AAR data available.

Those loads mostly consisted of plastic materials and resins such as polyethylene, polypropylene, polyvinyl
chloride, according to AAR commodity statistics.

What regulations exist?

Hazmat rail transportation is overseen by multiple organizations, including the Federal Railroad Administration, the Pipeline and Hazardous Materials Safety Administration, and the U.S. Department of Homeland Security, according to the AAR.

Railroads work with local, state and federal agencies to plan train routing, security, tank car design, and emergency response.

Under federal law, for example, rail customers must disclose and label hazardous materials shipments. That way the appropriate railcars are used and emergency responders are better informed, should an accident occur.

The classification of flammable rail cars also was a point of contention in the wake of the Ohio derailment.

The DOT divides classifications of hazardous material by varying levels of flammability and toxicity.

The train in Ohio didn’t qualify as a high-hazard flammable train (HHFT) — a designation that triggers other federal safety requirements.

The National Transportation Safety Board in 2014 argued for a broader definition of HHFT that covered Class 2 flammable gases — a category that includes vinyl chloride, which was being carried on the train that derailed in Ohio.