The 10th "Winter Spare the Air" alert of the season has been issued for Saturday, according to the Bay Area Air Quality Management District.
The alert means that Bay Area residents will not be able to burn wood for 24 hours because a high-pressure weather system has caused an unhealthy level of wood smoke and particle pollution in the air.
"Wood smoke is the other 'second-hand smoke,'" air district executive officer Jack Broadbent said in a statement. "In the Bay Area, it's the single largest source of air pollution on still winter days."
Residents are not allowed to use fireplaces, woodstoves, fire pits or other wood-burning devices on Saturday.
Homes where those items are the only source of heat are exempt from the restriction, according to the air district.
First-time violators will be given the option of taking a wood smoke awareness class, but will be fined $500 for a second offense.
The Winter Spare the Air season runs from Nov. 1 through Feb. 28.
Residents can call (877) 4-NO-BURN to learn whether an alert has been issued each day. People can also sign up to receive alerts at www.sparetheair.org.
