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Smoky air lingered over a large swath of Southern California Thursday as firefighters aided by calmer weather increased containment of two large blazes that forced widespread evacuations.

A smoke advisory was in effect following the two fires that broke out in brushy hillsides of Orange County Monday amid fierce winds and extremely dry weather conditions.

A thick haze blanketed much of the area and officials urged people to stay indoors if they smelled smoke or saw falling ash.

The air quality was unhealthy for sensitive groups across much of heavily-populated Orange and southern Los Angeles counties on Thursday, the South Coast Air Quality Management District said.

Wind shifts expected later Thursday could push the smoke toward the northeast and out of Los Angeles County, the district said.

The two fires prompted the evacuation of about 100,000 Orange County residents. As firefighters beat back the blazes amid subsiding wind speeds, most people on Wednesday were allowed to return home.

The Silverado Fire was 40% contained Thursday after burning 21 square miles (54 square kilometers) of brush about 35 miles (56 kilometers) south of Los Angeles.

No homes were lost but two firefighters remained hospitalized after suffering second- and third-degree burns over large parts of their bodies, Orange County Fire Authority Chief Brian Fennessy said.

Just to the north, the 22-square-mile (54-square-kilometer) Blue Ridge Fire near Yorba Linda was 30% contained on Thursday. It destroyed one building and damaged seven others.

The fierce winds that fanned the fires subsided Tuesday night and calmer breezes were expected into the weekend.

But continued warm and dry weather that make for potentially dangerous wildfire conditions were forecast into November, with no rain expected.