Flames devoured swaths of brush and trees in Northern California on Wednesday amid unseasonably hot and dry weather. Officials said wind-whipped flames led two firefighters to deploy the emergency fire shelters they carry.

The firefighters were assigned to the Glass fire burning in wine country north of San Francisco Sunday when gusty off-shore winds fanned the fire, prompting them to deploy their fire shelters after flames overwhelmed them.

The firefighters covered themselves on the ground with the emergency shelters that look like space blankets if they are in imminent danger from flames. They were not injured, the California Department of Forestry and Fire Protection said.

It’s the third time that fire crews have had to deploy their fire shelters this fire season — a last-resort effort to save their lives that was once uncommon. On Sept. 8, 14 firefighters deployed emergency shelters as flames overtook them and destroyed the fire station they were defending in the Los Padres National Forest. Three firefighters were hospitalized and later released. A day later, a crew fighting a deadly blaze in Butte County was overrun by flames when winds shifted and its members escaped with only minor injuries after deploying emergency shelters.

Heavy winds that spread new fires this week in the Napa and Sonoma wine country and in a far northern area of the state were reduced to breezes. But vegetation remained ripe for burning in high temperatures amid very low humidity.

Numerous studies in recent years have linked bigger wildfires in America to global warming from the burning of coal, oil and gas, especially because climate change has made California much drier. A drier California means plants are more flammable.

The National Weather Service said the weather conditions would last for several days because of high pressure centered over the state. Heat advisories were in effect or pending along about three-quarters of the California coast, and many areas had poor air quality because of smoke.

About 70,000 people were under evacuation orders in the wine region north of San Francisco where the Glass Fire has incinerated at least 80 homes along with winery installations and other buildings.

The Napa County Sheriff’s Office posted photos and video of a hellish scene of fires raging on forested hillsides at midnight close to a highway in the western part of the county.

About 150 miles to the north, there was no containment reported for the Zogg Fire, which also erupted during Sunday’s high winds and grew quickly, killing four people.

A man evacuated with severe burns Sunday, the day the Zogg Fire started burning in Shasta County, died at a hospital of his injuries Tuesday, said Shasta County Sheriff Eric Magrini. He was the fourth person killed by the blaze that has spread to neighboring Tehama County.

The Glass and Zogg fires are among nearly 30 wildfires burning in California. Fire-related deaths total 30.