NAPA COUNTY, Calif. – Investigators are looking at the cause of an early morning fire on Sunday that destroyed a structure that a witness said was a drug lab.

At 4:42 a.m. Sunday Napa County, Calistoga and St. Helena City fire departments were dispatched to a fire in the 100 block of Petrified Forest Road in unincorporated Napa County, according to Pete Muñoa, Cal Fire battalion chief and Napa County fire marshal.

He said the 911 caller reported a fire with explosions in the backyard of a residence.

Fire department units arrived to find a well involved structure approximately 400 square feet in size, according to Muñoa.

Muñoa said a witness stated to fire personnel at scene that they believed the structure to be a drug lab.

This statement accompanied with the earlier report of explosions forced crews to take a defensive attack on the fire to limit their exposure to possible hazardous materials, he said.

Investigators from the Napa County Fire Marshal’s Office in conjunction with the Napa County Sheriff’s Office are investigating the blaze, Muñoa said.

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