The U.S. Chemical Safety and Hazard Investigation Board (CSB) has released an update on its investigation into the September 29 BioLab fire in Conyers, Georgia, that shrouded neighborhoods in chemical smoke for days and forced thousands of residents to shelter in place or evacuate.
BioLab officials told the investigators they had established a permanent fire watch two or three months prior to the incident after strong odors from oxidizers in two storage buildings were detected, according to the CSB report. BioLab also told CSB two employees were on duty for fire watch on September 29.
Around 5 a.m., the CSB report said, one of the employees assigned to a storage warehouse – plant 12 – reported “hearing a popping sound,” and “recognized that the product was wet,” so called the other employee on duty.
The warehouse that caught fire contained 99% trichloroisocyanuric acid (TCCA) – used to make chlorinated tablets to control bacteria and algae – and 99% dichloroisocyanuric acid (DCCA), which is used to make swimming pool shock – a treatment used to help break down contaminants.
When TCCA touches a small amount of water and doesn’t dissolve, “it can experience a chemical reaction, generating heat and causing the decomposition of the chemical, which in turn produces toxic chlorine gas and can produce explosive nitrogen trichloride,” a 2023 report by the CSB said.
According to the CSB report, BioLab employees were unable to get control of the situation by isolating the product that was reacting, and with “large toxic vapor plumes” growing inside the building, they called 911 at about 5:10 a.m.
“By 6:30 a.m., flames were visible through the roof above the area where the employees had first observed the chemical reaction and off-gassing. The first shelter-in-place order was issued at approximately 7:40 a.m.,” the report said.
The fire was put out by around 8:10 a.m. by the Rockdale County Fire Rescue. But around noon, another fire erupted, according to the CSB.
The second fire produced thick black smoke and multicolored clouds of smoke, prompting evacuations of the area just before 12:30 p.m. Nearby Interstate 20 shut down just before 1 p.m., according to the report. It remained closed until the next morning.
View this interactive content on CNN.com“While this major interstate was reopened, smaller roads near the facility remained closed, and the Rockdale County Emergency Management Agency continued to issue nightly shelter-in-place warnings to the surrounding community within a 2-mile radius for several weeks after the incident,” the CSB said.
The Rockdale County Fire Chief said the fire was extinguished at about 4 p.m. But off-gassing of the chemicals at the plant continued because reacting TCCA product was still beneath the collapsed walls and debris of the warehouse building, requiring the use of heavy equipment to access and remove the material for treatment.
“BioLab has a strong track record of working constructively with regulatory agencies and will continue to cooperate with the CSB’s investigation,” the company said in a statement to CNN. “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 CSB said the investigation is ongoing and will release a final report when it is ready.
For days, shifting winds swept the chemical haze back and forth in multiple cities, including parts of Atlanta – about 30 miles away. Rockdale County issued a shelter-in-place advisory for 90,000 residents, and about 17,000 residents had to evacuate, CNN previously reported.
CNN spoke recently with several Conyers residents who said they still have blurry vision, shortness of breath, throat irritation or chronic headaches since the chemical plant fire.
Chlorine and hydrogen chloride were detected at high concentrations for several days based on the U.S. Environmental Protection Agency air monitoring results, according to the report.
The EPA discontinued its air monitoring on October 17, and the Georgia Environmental Protection Division assumed oversight of the plant’s remediation and cleanup.
Last month, Rockdale County officials announced plans to file a federal lawsuit seeking compensation for the county and impacted residents, and said they will work to have BioLab “permanently shut down” in the county.
CNN’s Holly Yan contributed to this report