The U.S. Chemical Safety and Hazard Investigation Board has released an update on its investigation into the BioLab fire, the September 29 inferno that engulfed a BioLab industrial building, shrouding neighborhoods in chemical smoke for days and forcing thousands of Georgia residents to shelter in place in each night or evacuate altogether.

The U.S. Chemical Safety and Hazard Investigation Board released an update into the investigation of the chemical reaction and toxic gas release that caused a massive fire at the Bio-Lab facility in Conyers on Sept.

The safety board said the primary substances involved in the Sept. 29 chemical release and fires were water disinfectants often used as a source of chlorine.