At noon Wednesday, the first Spare the Air period took effect, the San Jose Mercury News reported. The ban applies to fireplaces wood stoves and outside fire pits.

Violators face heavy fines if they are caught. Officials in the Bay Area Air Quality Management District say the law will be enforced, with inspectors roaming the area on Spare the Air Days looking for telltale signs of wood smoke drifting up from chimneys.

Kristine Roselius, a spokeswoman for the district, said about one in every seven residents of the region suffers from respiratory problems that could be aggravated by wood smoke.

"We take this very seriously," she said.

The district expects that 20 Spare the Air bans will be declared during the winter season.