The source of a hazardous materials fire that prompted a 12-hour shelter in place advisory for some Ceres residents on Monday was determined to be a light bulb.
An employee at Stanislaus Farm Supply on East Service Road was changing a light bulb inside a 40,000-square-foot warehouse that contained a large amount of fertilizer-grade sulfur, said Dustin Bruley, supervisor of the Stanislaus Regional Fire Investigation Unit.
“In those warehouses they have a lot of dust floating in the air attributed to that product and when you change out a light bulb the simplest spark or static electricity can set off the particulate that floats in the air,” Burley said. In this case the particulate was flammable sulfur.
He said the spark caused flash fire, “The air around it has this matter floating so when it ignites, anything in that room has the potential to ignite as well.”
A 500-ton pile of fertilizer sulfur began smoldering. Employees tried to put it out but the fire grew larger than they could handle.
More than 50 personnel responded to the scene from fire agencies, law enforcement and the Department of Environmental Resources.
A precautionary shelter in place order was issued for a 1-mile radius of the incident. Residents were notified by reverse 911 calls and posts on social media.
Hazmat personnel monitored the air on the perimeter of the property as well as adjacent streets and neighborhoods, according to a Modesto Fire Department incident summery.
“Hazmat personnel confirmed normal atmospheric readings throughout the incident,” the summery said.
Firefighters put water on the fertilizer sulfur and front loaders were used to break it up.
Firefighters cleared the scene at 1:09 a.m. Tuesday.