The Bay Area Air Quality Management District has issued a Spare the Air Alert for the entire Bay Area for Saturday.
Burning wood or any other solid fuel, such as manufactured fire logs, is prohibited for 24 hours both indoors and outdoors, air district officials said.
"Air pollution from wood smoke is one of the greatest health threats to Bay Area residents during the winter months," BAAQMD Executive Officer Jack Broadbent said in a statement. "Just one burning fireplace can create unhealthy air for an entire neighborhood."
Using fireplaces, wood stoves, pellet stoves, outdoor fire pits or any other device that burns wood is illegal when a Spare the Air Alert is issued, air district officials said.
First-time violators will be fined $100, or they must take a wood smoke awareness class. A second violation results in a $500 fine and the fines for subsequent violations are more.
Homes with wood stoves or fireplaces as the only source of heat are exempt until Nov. 1, when the wood-burning device must be Environmental Protection Agency-certified and registered with the air district, according to air district officials.
Residents can also check by signing up for AirAlerts at sparetheair.org or for phone alerts at (800) 430-1515.
Residents can also check on apps for iPhone and Android phones.