While the worst of the Northern California wildfires are almost extinguished—the Nuns, Pocket, and Tubbs fires are now 99 percent contained—danger may not be over even after the flames subside.
As Wired reports, huge urban fires poses particular hazards after clean up, as toxic substances from destroyed buildings may linger in the ashes.
Says the magazine:
“For how many structures that were burned in fairly small areas in these fires, I think that's a first-of-its-kind event,” says Geoffrey Plumlee, associate director of environmental health for the U.S. Geological Survey. “The concern is, can they get it cleaned up before the heavy rains come?”
[...] Depending on how combusted the ash is, it’ll have different chemical compositions. And that’ll mean the ash will mix either better or worse with underlying soil. Water won’t stick to more hydrophobic ash, so rainfall might run off faster, carrying away the surrounding soil as sediment. More hydrophilic ash might mix into the water and wash into nearby streams.
The ash running into those waterways could carry deadly lead or asbestos with it, or the fire remains could do even stranger things, like turn to vast fields of limestone or generate huge algae blooms that strip oxygen from rivers.
Being a singular event, it’s difficult to tell which of the frightening scenarios is truly plausible. But the toxic aftershocks of an inferno are commonly cited hazards for survivors even in the short term.
“There can be chemicals and asbestos and lead, plus plastic particles” and other dangerous substances loose at the sites of burned homes, Christine Sosko, Sonoma County director of environmental health, warned returning evacuees.
The California Air Resource Board says that those cleaning up burn areas should cover bare skin, wear a mask, and “avoid getting ash into the air as much as possible” by sweeping gently, wet mopping regularly, and avoiding operating machinery like vacuum cleaners or leaf blowers.
“If ash is wet down, use as little water as possible,” cautions the board.
Montana State University’s Department of Earth Sciences warns, “Over 90% of emissions from fires are small enough to enter the respiratory system” and that “particles in the air are able to travel deep into the respiratory tract,” principally a caution about smoke but also applicable to floating ash.
The pending cleanup will probably be the largest fire recovery drive in California history, calling on an a virtual alphabet soup of government agencies, including FEMA, the EPA, and California’s Office of Emergency Services (COES).
In Santa Rosa, ABC7 reports that COES has offered to haul away all materials from destroyed homes, but some families insist on handling the matter themselves for insurance purposes.