What came in, and what it does to people
Wildfire smoke is mostly fine particulate matter — the fraction the EPA classifies as PM2.5, particles 2.5 micrometres and smaller — together with carbon monoxide and volatile organic compounds, and, when the fire was burning houses rather than brush, the metals and plastics of a neighbourhood. The EPA's wildfire indoor-air guidance identifies the fine particles as the biggest health threat in smoke: small enough to get deep into the lungs, where they aggravate heart and lung disease, and linked to premature death in people with those conditions. The American Lung Association's wildfire page lists the groups it hurts first — children, older adults, pregnant people, and anyone with asthma, COPD or heart disease — and the everyday symptoms: burning eyes, runny nose, scratchy throat, coughing, wheezing, headaches, and chest tightness or shortness of breath in the people who are already vulnerable.
The part most households miss is that the exposure does not end when the plume does. A house that sat inside the smoke for days took the particulate in through every gap and let it settle: on the floors and counters, inside cabinets, across the top of the attic insulation, and through the return grille into the ducts, which the furnace fan then redistributes every cycle. The smell on the third warm afternoon is those residues re-emitting. The California insurance regulator's task force on smoke claims, convened after the January 2025 Los Angeles fires, put it in a sentence that applies to the health question as much as to the claim: particulate-bound residues do not dissipate until physically removed, and where the fire was a wildland-urban interface fire the residue carries greater potential for lead, asbestos and heavy metals than a brush fire's would.
The first week: reading the numbers and lowering the dose
Outdoors, the number to watch is the AQI. AirNow's scale runs in six colour bands: from 101 (orange) members of sensitive groups may experience health effects; from 151 (red) everyone may; from 201 (purple) the health alert applies to everyone; and AirNow's fire and smoke map shows the monitors and the plume together. Indoors, there is no public number, which is exactly the problem: the outdoor reading tells you when to close up and when to open the windows, and nothing about what is on the surfaces once you do.
For the days the smoke is still present, the EPA's playbook is the one to follow: keep windows and doors closed, run the central system on recirculate with the highest-efficiency filter it tolerates, do not add to the indoor load (no candles, no frying, no vacuuming without a HEPA vacuum), and set up one clean room — a bedroom with the door shut and a portable HEPA air cleaner sized for it, chosen with the EPA's guide to air cleaners in the home — where the household's most vulnerable person spends the worst hours. Ventilate when the outdoor reading drops. In the heat that trade-off is real, which is why the clean room, not the whole house, is the practical unit of protection.
Two things belong on the first-week list that are not in any health guidance. Bag the furnace filter that ran during the plume and keep it; it is the best record of what the house breathed. And photograph every room, especially any visible ash, before anyone wipes. Both are for the test and the claim that come next, and both are lost the moment cleaning starts.
Who moves back in, and when
A healthy adult who ventilates, filters and cleans hard surfaces with soap and water is taking a modest risk in a house that smells of smoke. The calculus changes for the people the lung association lists, and it changes again if ash was visible indoors or the fire consumed structures. For those households the honest answer to "is it safe to sleep here" is a measurement, and the measurement is a Certified Industrial Hygienist's or environmental consultant's sampling of the surfaces and the air, compared with outdoor and unaffected reference samples so that the result is specific to the house rather than a comment on the season. United Policyholders, whose guidance is written for exactly this moment, tells families who must move back before they are sure to at a minimum use a certified air cleaner, to report health problems to their doctor, and to be prepared to advocate for thorough inspections, testing or second opinions.
The attic deserves its own paragraph, because it is where the residue concentrates, where nobody looks, and where the stack effect pulls air from into the living space every night. Smoke odor in decking and attic insulation explains the building science; the practical rule is that nobody from the household goes up there, the hygienist samples it, and a roofer or engineer looks at the deck if embers or heat reached the roof. Our page on the attic after a fire covers what is in the insulation and who is breathing it.
Then the claim, with the same report
Here is the piece of good news in a bad week: the test that answers the health question is the document that settles the insurance claim. Standard homeowner and renter policies, in the words of Washington's insurance regulator, typically cover sudden and accidental smoke damage, including ash, from wildfires, paying for cleaning, deodorising and repairs plus temporary living costs if the home is not safe to occupy — and the regulator tells claimants to request an inspection that includes attics, crawl spaces, insulation and HVAC, and to photograph before cleaning. The carrier's usual position in a house that did not burn is that the residue is dust and the odor will fade; the hygienist's report, with its laboratory table and its background comparison, is the answer the adjuster has to respond to in writing. The claim-side guide on our sister site walks through the deadlines and the sequence.
The order, then, is the same for the health question and the money question: measure, then clean to what the measurement found, then measure again before the family moves back in for good. A restoration crew that arrives before the hygienist is offering to remove the evidence for both.