More than 90,000 residents in a county east of Atlanta were told to keep sheltering in place Monday and businesses were told to stay closed a day after a chemical plant fire sent a massive plume of dark smoke high into the sky that could been seen from miles away.

Air quality surveys done by the Environmental Protection Agency and the state Environmental Protection Division “revealed the harmful irritant chlorine” detected in the air from the fire at the BioLab plant in Conyers, Georgia, the Rockdale County Government said in statement early Monday.

“For everyone sheltering in place, the best practice is to turn the air conditioning off and keep windows and doors shut,” the statement said of the accident that has affected the entire county.

The fire was brought under control around 4 p.m. Sunday, officials said.

Interstate 20, which was shut down in both directions in the area on Sunday, was reopened Monday morning, officials said.

People in the northern part of Rockdale County, north of Interstate 20, were ordered to evacuate on Sunday and others were told to shelter in place..

Sheriff’s office spokesperson Christine Nesbitt did not know the number of people evacuated, although it covered a large portion of the community of Conyers. Media reports said the number was 17,000.

The fire ignited when a sprinkler head malfunctioned around 5 a.m. Sunday at the BioLab plant in Conyers, Rockdale County Fire Chief Marian McDaniel told reporters. The malfunction caused water to mix with a water-reactive chemical, producing a plume of chemicals.

McDaniel said there were employees inside the plant but no injuries have been reported at this time, The Atlanta Journal-Constitution reported.

BioLab’s website says it is the swimming pool and spa water care division of Lawrenceville, Georgia-based KIK Consumer Products. Automated messages at two phone numbers for the company said to call back during business hours. An email was sent to the company Monday.

“We are actively responding to an occurrence at our facility in Conyers, Georgia,” a BioLab representative said in a statement provided to the Journal-Constitution. “Our employees are accounted for with no injuries reported. Our team is on the scene, working with first responders and local authorities to assess and contain the situation.”

A small fire on the plant’s roof was initially contained but reignited Sunday afternoon, authorities said.

(AP)