A firefighter battling the explosive Kincade Fire near Geyserville was forced to deploy his personal fire shelter to prevent two residents from being overcome by flames as the blaze surged Friday evening, state officials said.

Fire shelters are used as a last resort, and the rescue, at about 6:20 p.m. Friday, prompted deep alarm among crews at the Sonoma County blaze.

Cal Fire said the firefighter and the two civilians were expected to survive. All three were taken by ground ambulance to a hospital “for evaluation,” Cal Fire said in a statement. “All injuries appear to be non-life-threatening.”

Fire shelters, which resemble blankets and deploy from shoebox-size waist packs, reflect heat while preserving a pocket of breathable air.

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“While working on an active portion of the fire, the firefighter came across two civilians who were attempting to evacuate from the fire when fire activity intensified,” officials said. “At that point the firefighter was forced to deploy his fire shelter, where he shielded them from fire.”

The three were not identified.

In June 2007, at the Angora Fire in and around South Lake Tahoe, a pair of Forest Service firefighters became trapped by flames while trying to save homes. Facing death, they ran to a meadow, ducked under their shelters and waited.

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They stayed under for 25 minutes, with no safe way to find out whether the danger had passed. Finally, a safety officer walked up and told them they were safe.

Lizzie Johnson is a San Francisco Chronicle staff writer. Email: ljohnson@sfchronicle.com Twitter: @lizziejohnsonnn