The Clayton Fire Department, with support from the Johnston County Fire Marshal's Office, said it has completed the investigation into the commercial fire alarm incident at 853 Shotwell Road.
Because of the extent of the damage and limited indoor camera angles, the exact cause of the fire could not be determined.
On Tuesday, Johnston County Emergency Services told ABC11 that the Clayton Fire Department, Raleigh Hazmat unit, North Carolina Emergency Management, and Johnston County Emergency Services were all at the scene "of an incident" at Bay State Pool Supply in Clayton.
Firefighters were working to identify the source of a plume in the area.
On Wednesday, investigators confirmed that the fire activated the building's sprinkler system, and water from the sprinklers came into contact with sodium hypochlorite inside the Baystate Pool Supplies suite. This produced hypochlorous acid and led to the chlorine-like odor observed during the initial response.
An industrial facility northwest of the incident was evacuated as a caution. There is an apartment complex nearby.
Clayton Police Chief David Ranes said it all started with a fire sprinkler activation at Baystate Pool Supplies, but when they arrived, they couldn't confirm a fire, and quickly realized that toxic pool chemicals were the primary concern.
"This product, you typically put it in a pool. So this product and a lot of water is great. A little water on this product, it reacts differently," Ranes said.
Emergency personnel had to call in Raleigh Hazmat to help, determining that sodium hypochlorite - or chlorine-based bleach - was released into the air after those fire sprinklers went off. Ranes said there appeared to be smoke coming from the business, but they still haven't been able to confirm the source, or whether there was even a fire to begin with.
"Raleigh Hazmat says there are multiple pails in there that are melted down. They're not sure the reason for the meltdown was a chemical reaction, was it a fire," Ranes said.
An hours-long cleanup was still in progress late Tuesday night as the Hazmat teams worked to neutralize the chemical release. Emergency officials say they're monitoring the air quality and tracking wind direction, but that there's no danger to the public and no further evacuations are planned.
"We've been monitoring some plume models at projects where the plume is going to go based off the wind directions. So we've been monitoring that, been in contact with a local now one center and just getting that information out to the public," said Ryan Parker with Johnston County Emergency Services.
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