The extinguishing of the fire was initially problematic because once the asphalt ignited it produced smoke so thick and hot that the firefighters could not come near enough the fire to start putting it out.
"Anybody breathing that stuff should be very concerned about what's getting into deep tissue, into the bloodstream", Carman said. "So I suspect that product will still be holding heat for another 24 hours".
In all, 21 people sought hospital care as a result of the fire, and all but one has been released. The person was listed in good condition.
The EPA said it eventually shifted resources in the evening to monitor the community.
The EPA is monitoring air quality in the area, according to federal on-scene coordinator David Morrison.
"While yesterday was a very scary day, it had the potential to be absolutely catastrophic". Thursday, April 26, 2018.
"In one of the largest disasters this community has ever seen, everybody is going home", he said.
Most of Superior was covered by the order.
A five-kilometre radius around the refinery, and 16-kilometre swath south of the plant was under an evacuation order, due to concerns about the smoke.
"Right now we have confirmation that that unit was not compromised whatsoever", he said.
"Once we understood the full response plan, yes, I think it was our responsibility", he said, adding that he and his team meant to publicly lay out the potentially unsafe situation at a 7 p.m. press conference Thursday.
Investigators searched for the cause of the massive Thursday morning explosion at the refinery, capable of processing up to 38,000 barrels of oil a day, which shook the city of Superior, Wisconsin, home to about 27,000 people. It began, said refinery manager Schade, as a typical day.
"That was the nature of the evacuation", Paine said. "We've got to be pretty proud of our little city of Superior", Hale said. "We needed that process to happen as smoothly as possible while we prepared for any eventuality at all".
"So while we were trying to be transparent, we were trying to truly protect the public as well". Fires reignited several times on Thursday, sending plumes of heavy smoke into the area. No deaths were reported, and officials said all workers had been accounted for.
"The emergency situation at the refinery is now over, and our focus in the days ahead will turn to the investigation and understanding the root cause of the incident", Husky Energy CEO Rob Peabody said in a statement. In more extreme cases, liver damage and cancer can occur if the exposure is more prolonged and extreme, the U.S. Environmental Protection Agency said.