(CNN)Five train cars that contained vinyl chloride, a potentially explosive chemical, are no longer burning after a train derailment in Ohio, a Norfolk Southern official said Tuesday.
The burning stopped after a controlled release of the unstable, toxic chemical Monday at the train derailment site in East Palestine, near the Pennsylvania border.
Four of those five cars have been cleared from the wreckage, and crews are working to remove the fifth car, Norfolk Southern official Scott Deutsch said Tuesday.
The train, which partially derailed Friday, had more than 100 cars. About 20 of those cars were carrying hazardous materials, said the National Transportation Safety Board, which is investigating the incident.
"There have been no reports of significant injuries -- either in the initial derailment or in the controlled detonation last night," Ohio Department of Public Safety Director Andy Wilson said Tuesday.
But it's not yet clear when residents who were ordered to evacuate can return home, East Palestine Fire Chief Keith Drabick said Tuesday.
"Once the Ohio Department of Health, the United States Environmental Protection Agency in conjunction with the East Palestine Fire Department and Norfolk Southern Railroad have determined that this is safe for East Palestine residents to return to their homes -- and, quite frankly, once I feel safe for my family to return -- we will lift that evacuation order and start returning people home," Drabick said.
'The detonation went perfect'
A black plume rises after the controlled detonation Monday in East Palestine, Ohio
Three days of anxiety about a potentially deadly explosion culminated in a loud boom Monday, when crews started the controlled release of vinyl chloride into a pit to burn it away.
A large plume of black smoke shot up toward the sky and the operation went as planned.
"The detonation went perfect," Deutsch said. "We're already to the point where the cars became safe. They were not safe prior to this."
Vinyl chloride is a man-made chemical used to make PVC and it burns easily at room temperature.
It can cause dizziness, sleepiness and headaches; and has been linked to an increased risk of cancer in the liver, brain, lungs and blood.
Breathing high levels of vinyl chloride can make someone pass out or die if they don't get fresh air, the Ohio Department of Health said.
The train derailment Friday led to a massive inferno and increased pressure inside the hot steel.
By Sunday evening, the burning wreckage threatened a catastrophic explosion capable of spewing toxic fumes and firing shrapnel up to a mile away, officials said.
Mandatory evacuations were ordered over several square miles straddling the Ohio-Pennsylvania border.
After the breach, officials detected "slightly elevated" readings of the phosgene and hydrogen chloride in the burn area and "only one minor hit for the hydrogen chloride downwind of the burn area" within the exclusion zone, the EPA's James Justice said Monday evening.
Such readings were expected after the controlled release, Justice said.
As for East Palestine's water supply, no impacts to the waterway were detected as of Monday evening, an Ohio Environmental Protection Agency official said.
A team will continue to monitor the air and water quality in the area, officials said.
Pennsylvania Gov. Josh Shapiro, who had also called for evacuations, said Monday evening that air and water quality is being monitored closely and no concerning readings had been detected so far.
But he told Pennsylvanians who live within 2 miles of the East Palestine derailment to keep sheltering in place with their windows and doors closed Monday evening.