Crews successfully completed a controlled breach of five derailed train cars Monday to reduce an explosion threat near the Ohio-Pennsylvania border, authorities said.
The "controlled release" of vinyl chloride began Monday afternoon amid the threat of a possible major explosion from the wreckage of a train carrying hazardous materials that went off the tracks Friday night in East Palestine, Ohio.
A loud boom followed by flames and a plume of black smoke spreading into the sky were seen at the derailment site Monday afternoon. According to a news release from Norfolk Southern Railway, the breach of several rail cars was completed successfully.
Norfolk Southern said some of the hazardous material is now burning off and is expected to drain for a short number of hours.
Authorities said Monday night that the situation will be monitored overnight but so far environmental agencies have detected "nothing alarming" in the air and water quality. Out of an abundance of caution, officials have asked people within two miles of the evacuation zone to remain indoors and continue to shelter in place.
Scott Deutsch, Norfolk Southern's regional manager for hazardous materials, said the daytime release would lower the risk of rail cars exploding and allow the fumes to disperse faster.
The Ohio National Guard and law enforcement officials blocked off roads Monday into East Palestine as hundreds of residents were warned of the dangers.
Authorities in the community of 4,761 people were enforcing what had previously been a strongly recommended evacuation zone within a 1-mile radius of the site where 50 cars came off the tracks Friday night, according to the village of East Palestine.
Within a two-hour period Sunday night, Ohio Gov. Mike DeWine said "a drastic temperature change" posed the threat of a "catastrophic tanker failure" that could send potentially deadly shrapnel up to a mile away.
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While around 500 people in the area refused to leave their homes by Sunday, officials said Monday that most, if not all, residents had left. Authorities continued knocking on doors Monday to ensure people were gone.
"You need to leave, we're ordering you to leave," DeWine said at an afternoon news conference to any remaining residents. "This is a matter of life and death, you are in imminent danger."
Referencing an evacuation map, DeWine had a stern warning: "If you're in that red zone, you're likely a very possible death, and if you're in the yellow zone, certainly severe, long term injuries."
Here's what to know about the Ohio train derailment:
What caused the Ohio train derailment?
About 50 Norfolk Southern train cars carrying products ranging from wheat and malt liquor to hazardous materials derailed Friday night in a fiery crash near the Pennsylvania state line. The train with three crew members on board was traveling from Madison, Illinois, to Conway, Pennsylvania.
A mechanical problem with a rail car axle caused the crash, according to federal investigators. The crew received an alert about the defect shortly before the accident, National Transportation Safety Board board member Michael Graham said.
While investigators have identified the exact "point of derailment," the NTSB was still working to figure out which rail car experienced the axle issue, according to Graham. A preliminary investigative report was expected within the next month.
What is vinyl chloride?
Of the train's more than 100 cars, Norfolk Southern said 20 were classified as carrying hazardous materials - defined as cargo that could pose any kind of danger "including flammables, combustibles or environmental risks."
Five of the 10 derailed cars carrying hazardous materials contained vinyl chloride, according to the NTSB.
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Vinyl chloride is used to make the polyvinyl chloride hard plastic resin in a variety of plastic products and is associated with increased risk of liver cancer and other cancers, according to the federal government's National Cancer Institute. Officials stressed Saturday that they had not confirmed any vinyl chloride release other than from pressure-release devices that were operating as designed.
"Short-term exposure to low levels of substances associated with the derailment does not present a long-term health risk to residents," according to a "Frequently Asked Questions" post on the village Facebook page.
The train's cars also carried combustible liquids, butyl acrylate and residue of benzene from previous shipments, as well as nonhazardous materials such as wheat, plastic pellets, malt liquors and lube oil, officials said.
What will happen if residents refuse to evacuate?
The Columbiana County Sheriff's Office announced its enforcement of the 1-mile evacuation zone in East Palestine on Sunday night because of the "high probability of a toxic gas release and/or explosion," the department said in a statement.
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Businesses, schools and several roads had closed in East Palestine by Monday. The East Palestine Police Department evacuated its communication center Monday while promising via social media that 911 emergency services would not be affected.
People refusing to evacuate may be arrested and charged with a misdemeanor and possible child endangerment if children are in the household, according to the sheriff's office.
"Please, for your own safety, remove your families from danger," authorities shared via social media.
Contributing: Emily Mills, Akron Beacon Journal; The Associated Press
This article originally appeared on USA TODAY: Toxic chemicals successfully released from cars on derailed Ohio train