The U.S. Chemical Safety and Hazard Investigation Board issued an investigation update Friday indicating fires at a BioLab facility near Atlanta that produced a toxic chemical cloud were caused by reactive chemicals being exposed to moisture.

The fires broke out Sept. 29 at the BioLab plant in Conyers, sending a huge plume of orange and black smoke into the sky.

BioLab makes chemicals that kill algae and bacteria in water, primarily for swimming pools and hot tubs, the report says. The company is a subsidiary of Lawrenceville, Georgia-based KIK Consumer Products.

A BioLab employee on fire watch at the Plant 12 storage warehouse reported hearing a "popping sound" upon leaving a break room to do a 5 a.m. check and immediately saw that a product reactive to water was wet, the report says. The employee called the only other BioLab employee on site.

Though no flames were initially observed, the employee on fire watch tried unsuccessfully to isolate the product and called 911 at about 5:10 a.m. as "large toxic vapor plumes" formed inside the building.

By 6:30 a.m., flames could be seen through the roof of the area where employees first noticed the chemical reaction. An initial shelter-in-place order was issued around 7:40 a.m., and the fire was put out by Rockdale County firefighters about 30 minutes later.

A second fire broke out around noon, producing "thick black smoke, followed by multicolor plumes," the report says. Evacuations of the surrounding area began around 12:30 p.m., and the county fire chief said the fire was extinguished by 4 p.m.

Interstate 20, which runs parallel to the facility, was shut down shortly after the building collapsed just before 1 p.m. and was closed until about 7 a.m. the next day. Smaller roads near the facility remained closed, and the Rockdale County Emergency Management Agency issued shelter-in-place warnings within a two-mile radius that lasted for several weeks. The final order expired Oct. 17.

Smoke drifted toward Atlanta, causing a smog or haze that smelled of chlorine in parts of the city and surrounding area.

"BioLab has a strong track record of working constructively with regulatory agencies and will continue to cooperate with the CSB's investigation, which still remains ongoing," a spokesperson from BioLab said in a statement emailed to Newsweek on Sunday.

"Our top priority is and has always been the health and safety of the communities within which we operate, and we worked collaboratively with first responders and local, state, and federal authorities to successfully remediate the situation at our Conyers warehouse storing chemicals that treat swimming pools and spas," the statement continued. "We remain firmly committed to understanding the causes of the incident and to making things right for impacted area residents and business owners."

More than a dozen lawsuits have been filed in connection with the fire.

Information from The Associated Press was used in this report.

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