Residents in the area near a North Carolina fertilizer plant that caught fire Monday night are urged to stay away from their homes for an “undetermined” amount of time, as a massive amount of ammonium nitrate within the burning facility is at risk of an explosion, officials said Wednesday. 

“At the beginning of this incident there was enough ammonium nitrate on hand for this to be one of the worst explosions in U.S. history,” Winston-Salem fire chief William “Trey” Mayo said at a press conference Wednesday. 

The fire broke out at about 6:30 p.m. on Monday at the Winston Weaver Company Fertilizer plant in Winston-Salem, North Carolina. No injuries have been reported and all employees are accounted for, officials said. 

Aerial view of the fire burning at the Winston Weaver Company Fertilizer plant in Winston-Salem, North Carolina.

Winston Salem Fire Department

According to Mayo, there were nearly 600 tons of ammonium nitrate and 5,000 tons of finished fertilizer at the facility. 

At high temperatures, ammonium nitrate can create toxic nitrogen oxide and ammonia and can cause an explosion. It is the chemical compound behind the deadly 2020 Beirut port explosion and a 2013 blast at a fertilizer plant in Texas that killed 14 people and injured nearly 200 others. 

Mayo said the unpredictability and complex nature of the compound has led crews to err on the side of caution. On Tuesday, officials estimated a 36-hour window where firefighters would wait to see how the burning plant’s chemicals reacted and potentially decrease the fire’s danger zone radius for the near 6,500 people urged to evacuate. 

But Mayo said on Wednesday that even a 48-hour timeframe to let the fire burn wouldn’t be enough time to ensure conditions are safe. 

“We’re just not going to be there,” the fire chief said. “We’ve got too much product, too many unknowns.”

Air quality monitoring devices as well as drone operations have continued to be deployed to assess the fire, but the city’s division fire chief Bobby Wade said crews are “not having a lot of improvement on the scene.”

He urged those in the area with respiratory issues to continue to take precautions like shutting windows and staying indoors as smoke from the fire pollutes the city’s air. 

North Carolina Governor Roy Cooper pleaded with residents within the fire’s danger zone to evacuate if they haven’t already. 

“They put other people at risk when they refuse to evacuate,” he said.