ATLANTA (AP) — Federal authorities have released an update on the investigation into fires at the BioLab chemical plant near Atlanta that produced a toxic chemical cloud and forced nearby residents to shelter in place.

The fires broke out Sept. 29 at the BioLab plant in Conyers, sending a huge plume of orange and black smoke into the sky. The U.S. Chemical Safety and Hazard Investigation Board on Friday released an investigation update.

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.

The company said in a statement that it has a “strong track record of working constructively” with regulators and will continue cooperating with federal authorities who are investigating.

"We remain firmly committed to understanding the causes of the incident and to making things right for impacted area residents and business owners,” the statement says.

A BioLab employee on fire watch at the Plant 12 storage warehouse reported hearing a “popping sound” as they left a breakroom 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.

Parts of the building where the initial reaction happened collapsed during the fire and the building was destroyed. The Plant 12 building covered an area larger than five football fields and remained an “active emergency response scene” for nearly four weeks, the report says.

The Plant 12 warehouse was a bulk storage area separated from the main warehouse by a firewall and fire shutters, the report says. BioLab told federal investigators they had established a permanent fire watch two or three months before the event “after detecting strong odors from oxidizers in two storage buildings,” including Plant 12.

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.

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