The best time to create a cleaner-air room is before smoke appears in the forecast, according to an updated federal guide that treats wildfire preparation as part of community health infrastructure rather than a last-minute household purchase.
The 2026 Wildfire Smoke Guide for Public Health Officials, released by the Environmental Protection Agency in June, provides a 136-page plan for limiting exposure in homes, schools, workplaces and public shelters.
The manual was developed by an interagency team that included specialists from the EPA, California Air Resources Board, Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, U.S. Forest Service and California health agencies. EPA senior environmental health scientist Susan Lyon Stone is listed as the project’s lead team member.
Fine particulate matter, or PM2.5, remains the principal pollutant used to manage smoke exposure. These particles can travel deep into the lungs and have been linked to effects ranging from irritation and asthma exacerbations to heart failure and premature death.
The new edition gives greater attention to prolonged smoke events, repeated exposure and emergencies in which smoke and high heat occur together. Closing windows may reduce particle entry, for example, but can create a dangerous indoor temperature in a home without adequate cooling.
For households, the guide recommends identifying one room that can be kept cooler and cleaner than the rest of the home. Doors and windows should remain closed when smoke is present, and activities that generate particles—such as smoking, burning candles or frying food—should be limited.
Air-conditioning systems with outdoor-air and recirculation settings should generally be placed on recirculation during a smoke event. Evaporative coolers can introduce large quantities of outdoor air, while single-hose portable air conditioners, range hoods and bathroom exhaust fans can create pressure differences that pull unfiltered smoke through openings elsewhere in a building.
Filtration must match the building. A central system can use the highest-efficiency filter it can safely accommodate, while a portable air cleaner should be sized for the room in which it operates. The guide advises against devices that intentionally generate ozone.
Where commercial cleaners are unavailable or unaffordable, the EPA identifies a well-built DIY unit using a newer box fan and furnace filters as a lower-cost alternative. Multiple-filter designs, thicker filters and a cardboard shroud can improve performance. Fans should have been manufactured since 2012 and carry an appropriate UL or ETL safety marking.
Preparation is important because filters and portable cleaners may become difficult to find after a smoke warning has been issued. Knowing how a ventilation system works is also considerably easier before residents are trying to interpret controls while outdoor particle levels are rising.
Monitoring is another part of the plan. The guide explains how regulatory stations, temporary monitors, lower-cost sensors, satellite observations and the Air Quality Index provide different views of an event. A dramatic satellite plume does not necessarily reveal the particle concentration at ground level, while an individual low-cost sensor may require correction and appropriate averaging.
Public agencies are encouraged to identify cleaner-air facilities in advance. The guide distinguishes shelters, where displaced residents may remain overnight or for days, from cleaner-air spaces that provide several hours of relief. Potential daytime locations include libraries, museums, malls, theaters, indoor sports facilities and senior centers.
Those buildings need sufficient filtration, temperature control and capacity for the people expected to use them. Communities with unhoused residents or households lacking air conditioning and filtration may benefit particularly from reliable public spaces.
Respirators can reduce exposure for people who must be outside, but they are not the first or only control. A NIOSH-approved N95 or P100 must fit closely to the face, and masks do not compensate for prolonged exertion in heavily polluted air. Children and some adults may also have difficulty obtaining an effective fit.
During an active fire, evacuation instructions take priority over sheltering indoors. Buildings can reduce exposure to transported smoke; they cannot provide protection from flames, rapidly approaching fire or other immediate hazards.
The guide’s central message is therefore larger than any single filter or room. Smoke readiness depends on buildings that can be adjusted, public spaces that have already been evaluated, air-quality information people trust and plans that account for both smoke and heat. Once the sky changes color, the most valuable preparations are the ones already in place.
