Residents and businesses were told to evacuate the area around the BioLab plant in Conyers, Georgia, after the blaze broke out early Sunday morning. A shelter-in-place advisory is ongoing for around 90,000 people in Rockdale County.
The plume from the chemical reaction that followed the outbreak of the fire could be seen for miles - and officials on Monday were cautioning those left in the area to stay indoors with their windows closed and air conditioners off.
Conyers is about 30 miles east of Atlanta.
Both sides of Interstate 20 reopened Monday after authorities shut down portions of the highway Sunday citing "unpredictable path and wind direction, which could change the direction of the irritants in the air."
County facilities in Rockdale County remained closed Monday. Some schools and daycares in neighboring Dekalb County canceled outdoor activities for the day. Residents in surrounding areas described a bleach or chemical smell in the air.
The fire broke out on the roof of the plant around 5 a.m. Water from what officials earlier described as a malfunctioning sprinkler head "came in contact with a water reactive chemical and produced a plume," county officials said in a statement.
Firefighters were able to contain the fire, but it reignited hours later, Rockdale County Sheriff Eric Levett said in a video message posted on Facebook.
The fire was extinguished around 4 p.m., Rockdale County Fire and Rescue Chief Marian McDaniel said, but the building's roof later collapsed.
Air quality surveys conducted by state and federal agencies "revealed the harmful irritant chlorine" coming from the facility, county officials said in a news release Monday morning.
Exposure to chlorine can cause burning of the eyes, nose and mouth, according to the Centers for Disease Control and Prevention. It can also lead to coughing, choking, nausea, vomiting, headache and dizziness.
CNN has reached out to BioLab, described as a manufacturer of pool and spa treatment products, for comment.
"This is not the time to do any type of sightseeing. We are strongly encouraging everyone, no matter where you're coming from, but especially Rockdale residents, to stay out of this area," Levett said.
About 17,000 people between Sigman Road and I-20 were asked to evacuate, according to Sharon Webb, director of the county's emergency management agency.
A nearby hospital began moving patients to other facilities as a precaution - and officials urged those having a medical emergency to go to another hospital or one in another county, Webb said.
It was "all hands on deck" situation, Rockdale County Chairman Oz Nesbitt told CNN's Jessica Dean. "All of our resources have been dispatched and deployed," Nesbitt said. "Every available agency, GEMA, FEMA, everyone is on deck here in Rockdale County, we're managing this situation as we try to get it under control."
The roof of the chemical plant building caved in after the blaze and Nesbitt described the damage as a "complete collapse."
Residents in neighboring Newton County on Sunday also received an alert about the situation in Conyers.
In September 2020, BioLab experienced a "thermal decomposition event" that also led to a fire that temporarily closed I-20.
In its final report on that incident, the US Chemical Safety Board found strong winds from Hurricane Laura damaged the lab's warehouse, allowing rainwater into the building. The water came in contact with a chemical and initiated a reaction that caused the fire.
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