Potential for ‘major explosion’ from derailed train, Ohio governor says.

Authorities warned Sunday night that a “major explosion” or toxic gas release could happen at the site of a train derailment in northeastern Ohio, ordering anyone within a mile to evacuate or face possible arrest.

A “drastic” temperature change on Sunday evening in one of the derailed cars — some of which were carrying hazardous materials when they went off the tracks Friday night — created the potential for an explosion that could cause “deadly shrapnel” to fly up to a mile, Ohio Gov. Mike DeWine (R) said in an 8:40 p.m. statement.

Teams were working to prevent an explosion at the site in East Palestine, Ohio, DeWine said. He ordered more than 500 people who were reported to have ignored evacuation orders to leave their homes. People who do not evacuate may be arrested, Columbiana County Sheriff Brian McLaughlin said on the agency’s Facebook page.

“There is a high probability of a toxic gas release and or explosion,” McLaughlin said. DeWine said he was sending the Ohio National Guard to the site.

The dire warning came nearly 48 hours after the crash occurred. Fifty cars of a 141-car Norfolk Southern train derailed about 9 p.m. Friday, igniting a large fire that still had flames burning Sunday and causing residents to evacuate.

Because some cars were carrying hazardous chemicals, including vinyl chloride and phosgene, firefighters could not safely put out the blaze. By Sunday afternoon, investigators said the area remained a hot zone.

DeWine’s statement did not indicate what had caused the temperature change that evening. It only said it had created the possibility for “a catastrophic tanker failure,” which would cause an explosion.

Earlier in the day, local authorities had urged people to stay away from the crash and the town, which is near the Pennsylvania border. Though exactly what, if any, chemicals were burning in the days-long fire — and whether it could cause any long-term effects for residents — remained unknown, investigators were beginning to piece together what had happened.

The derailment was likely caused by mechanical issues on one of the rail car axles, National Transportation Safety Board member Michael Graham said at a Sunday news briefing.

The Norfolk Southern train’s crew members, who were interviewed Sunday, got an alarm indicating a mechanical issue shortly before the train derailed; then, an emergency brake went on. Two videos also indicate there was a mechanical problem, Graham said.

Investigators don’t yet know how long it will take to clean up the site. Cleanup crews and investigators will have to wait until the site has been deemed safe to approach.

“We still have a hot zone,” Graham said. “When they say it’s safe to go in, then crews will be allowed in there to clean up the site.”

On Sunday, East Palestine Mayor Trent Conaway told people to avoid the one-mile radius of the crash, which had prompted him the day before to order about 1,500 residents to evacuate.

“Please stay away from East Palestine,” Conaway said at a news conference hours before the temperature change in one of the rail cars prompted the governor’s warning. “Please stay away from the wreck. I don’t want to say it’s a dangerous situation, but it is still a very volatile situation.”

A state of emergency will remain in the town until at least Monday evening, he said.

“As of right now, we are still not conducting any on-scene operations. … It’s still too volatile of an area,” East Palestine Fire Chief Keith Drabick said at the news conference. He added, “It’s just not safe to go in there and 100 percent identify which cars of that train … are actually burning.”

After workers get the all-clear, Graham said the cars carrying hazardous materials would be moved to a safe location where inspectors could analyze them. Meanwhile, the NTSB has gathered other evidence, including data from the train’s “black box” recorder, camera video and audio recordings. A drone also mapped the scene. The NTSB has requested inspection, maintenance and crew records from Norfolk Southern.

After the three crew members brought the train to a stop, the conductor detached the locomotives from the rail cars and moved to a safe location, Graham said. No injuries were reported. Authorities believe the crew “did exactly what they were expected to do,” Graham said.

Some of the rail cars contained hazardous materials, including carcinogenic vinyl chloride, according to officials. They said they were unable to answer whether vinyl chloride was burning.

The Environmental Protection Agency received a list from Norfolk Southern of chemicals the train was carrying, including phosgene — an industrial chemical used to make plastics and pesticides — which they are monitoring, said James Justice, who works with the agency’s Health and Ecological Criteria Division. That list will be released to the public, authorities said.

Justice said the EPA is also monitoring the presence of chemicals produced by the combustion, such as hydrochloric acid. As of Sunday afternoon, residents were told they did not need to wear face masks to protect them from potentially harmful pollutants, authorities said.

Authorities assured residents that their water was drinkable and that no dangerous emissions had been detected as of Sunday.

But some residents worried about what chemicals could be in the air and water as they sought a place to shelter until authorities say it’s safe enough for them to return.

East Palestine resident Eric Whitining evacuated the area Friday and returned Sunday afternoon.

“We are hardly smelling anything here,” Whitining, 42, who lives less than a mile from the derailed train, told The Washington Post, speaking hours before authorities warned of the potential for an explosion. “We are on the fence of whether we should leave or not.”

His family’s bags are still in the car, but he is unsure whether he should move to a hotel that will charge him about $300 a night for his family and his dog if workers at the scene, which he said he could see from his house, were not wearing masks.

“I don’t think their companies would allow them to work without masks if it were that dangerous,” Whitining told The Post. “It really gives the wrong signal.”

Authorities are testing the water quality, Kurt Kollar, a specialist with the Ohio Environmental Protection Agency emergency response unit, said at the news conference. Kollar said residents can continue to drink the water, which was not affected by the incident.

Thomas A. Crosson, a spokesman with Norfolk Southern, told The Post that potential well contamination was “improbable” because of where the train derailed.

The EPA is monitoring the area’s air quality, said Justice.

“We have not seen anything above established screening levels, but as the chief and the mayor have pointed out, it’s a dynamic situation,” Justice said. “Things can change at any moment.”

Conaway reiterated at Sunday’s news conference that the air in the town was safe, but he warned anyone traveling to the wreckage site — where one person had already been arrested on charges of misconduct in an emergency — “You’re breathing toxic fumes in.”