Authorities shut down an illegal cannabis extraction lab southwest of Santa Rosa this week after finding large amounts of highly flammable and volatile chemicals chemicals stored inside a warehouse, Sonoma County officials said Friday.

The operation was inside a 17,000-square-foot building in an unincorporated industrial area outside city limits. County officials said the inspection effort began after the property owner declined to allow inspectors inside during a previous visit.

Officials said a strong cannabis odor, loud machinery, visible unpermitted construction and past violations raised concerns, and neighbors had also raised concerns about the site. Based on those observations, a Superior Court judge approved an inspection warrant.

Sonoma County sheriff’s deputies accompanied inspectors when they entered the warehouse Wednesday.

Inside, authorities said they found workers running what they described as a multimillion-dollar hydrocarbon extraction operation. Hydrocarbon extraction uses gases like butane or propane to separate cannabis oil from plant material — the oil is later used in vape cartridges, edibles and other cannabis products.

It’s a method that requires strict ventilation and fire-safety systems because the gases are highly flammable. Officials said the chemical quantities inside the building were greater than anything previously found in Sonoma County.

Officials said the lab also failed to meet basic safety requirements, including proper electrical systems, fire protection equipment and permitted building alterations.

Removing the hazardous chemicals required a coordinated cleanup involving Permit Sonoma, the Sonoma County Fire District and the state Department of Toxic Substances Control.

County officials called the setup “life-threatening,” both for workers inside the warehouse and the surrounding area.

Authorities did not say whether anyone was detained or arrested. A sheriff’s spokesperson and a county representative could not be reached Friday afternoon. The investigation remains ongoing.

Illegal extraction and unlicensed cannabis operations have surfaced repeatedly in Sonoma County in recent years. In 2019, officials shut down a Santa Rosa property where more than 9,000 illegal plants and an unlicensed hash-oil lab were found — part of a two-year crackdown that closed 863 unpermitted grow sites countywide.

In 2018, a hash-oil lab explosion near Sebastopol burned two people and damaged a home. Later that year, a blast inside a Santa Rosa house was tied to a clandestine cannabis-oil setup, where investigators found butane canisters and extraction equipment.

Another suspected butane lab near Sebastopol was linked to fires and explosions in 2020, prompting renewed warnings from fire officials about the dangers of unregulated extraction methods.