(CNN)Residents of the Ohio village of East Palestine remain unable to return home after a controlled release Monday of a toxic chemical from cars that were part of a train derailment three days ago, Mayor Trent Conaway said during an evening news conference.
An operation to drain vinyl chloride -- a chemical that officials said was unstable and could explode -- from five Norfolk Southern rail cars began just after 4:30 p.m. ET.
Scott Deutsch of Norfolk Southern had earlier said small, shaped charges would be used to blow a small hole in each rail car. The vinyl chloride would then spill into a trench where flares would ignite and burn it away.
As of 7 p.m., the flames were reduced and a small fire continues in the pit, Deutsch said at the news conference.
It is "still an ongoing event so we just ask everybody to stay out," the mayor said. "We have to wait to the fires die down."
An evacuation zone of 1 mile around the train's crash site remains in place, Conaway said. Authorities will reassess the zone Tuesday morning, he added. "We really don't have a time frame right now" for the return of residents, he said.
A team from the Environmental Protection Agency will monitor the air and water quality in the area, officials said.
The remaining fires will go out on their own and won't be extinguished by crews, Deutsch said.
Prior to the controlled release Monday, officials worried the five derailed cars carrying vinyl chloride might hurl toxic fumes into the air and shoot "deadly shrapnel" as far as a mile away.
One rail car in particular had been a focus of concern because its malfunctioning safety valves had prevented the car from releasing the vinyl chloride inside, a Columbiana County Emergency Management Agency official and a Norfolk Southern spokesperson told CNN earlier Monday.
Ahead of the controlled release, the evacuation zone surrounding the fiery derailment site expanded to two states, Ohio Gov. Mike DeWine said.
DeWine and Pennsylvania Gov. Josh Shapiro had ordered evacuations for a 1-mile-by-2-mile area surrounding East Palestine, a village of about 5,000 people near the Pennsylvania border, DeWine said.
This followed evacuations that took place just after the massive inferno began Friday night.
According to East Palestine resident Eric Whiting, police knocked on his door about an hour after the derailment and asked the family to evacuate.
"They told me they didn't know anything yet, but they just needed us to evacuate," Whiting told CNN.
Officials begged residents for several days to leave the area as fears about air and water quality have mounted.
Mayor Conaway said Monday he was "proud of the citizens" as everyone cleared out when officials went door-to-door and there were no arrests.
Here's the latest on the ground:
• Police shift communications hub: The scene was so dangerous by Monday