Here’s what the derailed Ohio train was carrying — and what was burned

Feb. 3: Minutes before derailment

A security camera captured the Norfolk Southern train near Salem, Ohio, 20 miles west of the site where it later derailed. What appears to be sparks and flames can be seen underneath one of the cars. The National Transportation Safety Board (NTSB) has since said that the derailment appears to have been caused by a mechanical problem on one car, saying a wheel bearing on that car appeared to have overheated.

Feb. 3: The accident

Around 9 p.m. on Feb. 3, approximately 50 cars derailed near the village of East Palestine, Ohio, a town of 4,700 residents just half-a-mile from the state border with Pennsylvania. The crash caused a fire spanning the length of the derailed cars.

Eleven of the derailed cars contained hazardous materials, some of which are used to make plastics. Vinyl chloride, a cancer-causing substance, was among the primary chemicals released in the crash, according to Ohio Environmental Protection Agency spokesman James Lee.

Vinyl chloride also releases other chemicals when it burns, many of which can be harmful to humans, experts say. Exposure to these chemicals can cause eye or throat irritation, as well as dizziness, nausea or headache.

The risk of coming into contact with the hazardous chemicals, as well as possible explosions, meant that firefighters could not immediately put out the blaze.

Feb. 6: The controlled release

Two days after the crash, officials monitoring the situation said there was serious concern one of the cars would explode in a “catastrophic” blast, according to Ohio Gov. Mike DeWine (R), as the temperature in the car rose.

Authorities ordered the evacuation of about 1,500 residents and initiated a controlled release of vinyl chloride from five train cars to avert an explosion, sending a toxic plume into the air.

Measuring the impact

In the following days, fears about a broader environmental disaster in East Palestine and neighboring areas began to mount.

Ohio Department of Natural Resources Director Mary Mertz said that about 3,500 fish died as local waterways including the Ohio River became contaminated. State officials said they had not collected any evidence of animals other than fish suffering from the spill, though residents have shared suspicions about chickens, rabbits, foxes and other animals falling ill.

Low levels of a chemical called butyl acrylate have been detected at multiple sampling sites along the Ohio River. State EPA officials have said that the concentrations detected pose no risk for drinking water supplies in the area.

Meanwhile, a pungent odor remains in the air in East Palestine, and some residents have complained of rashes, runny eyes and other symptoms.

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Once cleanup of the derailment site is completed, state and federal environmental officials said a wider effort will begin to uncover and address any contamination that may have spread into soil and groundwater. Anne Vogel, director of the Ohio EPA, said that process will take “as long as it takes.”

There are concerns the pollution could be pervasive, and questions about how widely contamination may have spread through the plume of smoke during the controlled chemical release. For now, authorities say the air is safe to breathe and the municipal water supply safe to drink.

Naema Ahmed and Scott Dance contributed to this report. Editing by Monica Ulmanu, Juliet Eilperin and John Farrell.