As cities have become more expensive, these areas have become increasingly attractive places to settle, and more than 12 million homes were built in this liminal space between 1990 and 2010. With more people in the woods, there are more structures to defend.

More than 80 people died in the Camp fire near Paradise last year; most lived in areas that were basically wilderness. Firefighters now have to contend with protecting people who live in areas that some consider uninhabitable and the fallout of homes burning in these isolated locations.

At base camp in Sonoma, many said they were aware of these expanding chemical dangers. Cal Fire has a research and development team that is working to develop better gear for firefighters, said Eric Castellanos, a captain with the department.

But there is division among firefighters about exactly what should be done to protect them. Mr. Alba, the firefighter who was in Paradise, is calling on fire agencies to remove PFAS from their uniforms, and for officials to come up with a solution that protects them from noxious threats.

But Scott Ross, a firefighter from Shasta County, said he worried that more restrictions — heavier gear, for example — would make it harder for them to do their work.

“This is not a safe job,” he said. “You can’t make it safe. And the more you try, the more you tie our hands.”

Tim Arango contributed reporting from Los Angeles, Nicholas Bogel-Burroughs from New York and Matt Richtel from San Francisco.