GILBERT, Ariz. -- The massive fire that blanketed the East Valley with thick, black smoke Monday afternoon was started by a discarded cigarette, according to the Gilbert Fire Department.
The fire leveled a long-standing plumbing company and destroyed millions of dollars worth of supplies.
Jack Stapley, a co-owner of Farnsworth Plumbing Supply Company, estimated $8 million worth of supplies burned.
He said a warehouse was destroyed and an office building facility was also badly damaged.
The business has been in Gilbert near McQueen and Baseline roads for 18 years.
The fire started shortly after 3 p.m. Monday and burned intensely for nearly three hours. As of 10 p.m., crews were still working to put out hot spots and cool down the grounds.
Firefighters were still on the scene Tuesday morning to keep an eye some little fires that were still burning and make sure they didn't blow up into another conflagration.
With Monday's massive flames came a series of explosions as propane tanks on the property blew up.
Employees of nearby businesses reported hearing the explosions and feeling vibrations.
"It was not unlike a very sudden earthquake, you could feel it through your feet and through the windows, it was like a bomb went off," said Carson Meyers, who works at a neighboring company that was evacuated as a precaution.
Other witnesses reported seeing debris fly through the air.
"Big, industrial shipping pallets flying 100 feet in the air," Peter Wendt said.
Stapley said the other branches of the Farnsworth company, which include a waterworks and air conditioning business, were not impacted and will be open for business Tuesday.
Close to 200 firefighters were brought in from Mesa, Chandler and Tempe to help Gilbert crews battle the flames amid intense temperatures that reached 113 degrees.