Wildfire smoke: keeping it out of the house

EPA's six steps for a clean room¹

"Choose a room.
It should be big enough to fit everyone in your household and comfortable to spend time in."
"Prevent smoke from entering the room.
Close all windows and doors in the room, but don't do anything that makes it hard to get out."
"Stay cool.
Run fans, window air conditioners, or central air conditioning."
"Filter the air in the room.
Use a portable air cleaner that is the right size for the room"
5
"Avoid activities that create smoke or other particles indoors, including:
- Smoking and vaping.
- Using gas, propane or wood-burning stoves and furnaces.
- Spraying aerosol products, such as cleaners or air fresheners.
- Frying or broiling food.
- Burning candles or incense.
- Vacuuming, unless you use a vacuum with a HEPA filter."
"Spend as much time as possible in the clean room to get the most benefit from it."

The rest of the house

EPA: "Keep windows and doors closed"²
EPA: "Choose a high-efficiency HVAC filter, such as one with a Minimum Efficiency Reporting Value (MERV) 13 rating, or as high a rating as your system fan and filter slot can accommodate."²

A box fan and a filter

EPA: "DIY air cleaners are made by attaching an air filter to a box fan with tape, brackets/clamps, or a bungee cord."³ What its research found:

"DIY air cleaners can effectively reduce smoke concentrations in a laboratory setting."
"DIY air cleaners were almost completely ineffective with dirty filters, highlighting the need for frequent filter replacement during smoke events; the duration of filter lifespan will vary with use and conditions."
"When building a DIY air cleaner, it is recommended to use only NEWER box fans (since 2012), which have the added safety features of fused plugs and thermal cutoffs."

On its fan safety tests, EPA adds: "There is a wide range of variability in the types of fans and filters used, and how these DIY air cleaners can be built or operated. Therefore, EPA cannot assure these results are representative of all scenarios."³

Filtering what is left

EPA: "Choose a portable air cleaner that is the right size for the room in which you will use it."²

Airthings Renew

Airthings says:⁴

"HEPA 13 filter removes 99.97% of all particles as small as 0.3 microns."
"Activated charcoal filter. Captures and holds gases (VOCs) and odors."

CARB's list of certified air cleaning devices includes one Airthings air purifier: model number AP-1, Executive Order G-24-049. Checked October 4, 2026.

See Airthings air purifiers

The small commission from purchases made through this link helps keep this free public directory open, at no extra cost to you.

EPA: "EPA neither certifies nor recommends particular brands of air filters or home air-cleaning devices including portable air cleaners or purifiers."⁵

If you work outdoors

California, Oregon, and Washington have their own wildfire smoke rules for outdoor work. Here is what each says.

California

Title 8, section 5141.1, Protection from Wildfire Smoke⁶

AQI 151 or more: "This section applies to workplaces where: (A) The current Air Quality Index (current AQI) for PM2.5 is 151 or greater, regardless of the AQI for other pollutants; and (B) The employer should reasonably anticipate that employees may be exposed to wildfire smoke."
AQI Over 500: "Where the current AQI for PM2.5 exceeds 500, respirator use is required."

Oregon

OAR 437-002-1081, Protection from Wildfire Smoke (PDF)⁷

The rule's scope, then two rows of its table of requirements by AQI.

AQI 101 or more: "This standard applies to public and private sector employers whose employees are or will be exposed to wildfire smoke where the ambient air concentration for fine particulate matter (PM2.5) is at or above 35.5 µg/m3 (Air Quality Index value of 101 for PM2.5)."
AQI 251 to 500: "Provide NIOSH-approved filtering facepiece respirators for mandatory use by implementing a Wildfire Smoke Respiratory Protection Program in accordance with Appendix A."
AQI 501 and above: "Provide NIOSH-approved respirators for mandatory use by implementing a Respiratory Protection Program in accordance with 29 CFR 1910.134."

Oregon OSHA's note: "The AQI values for mandatory respirator use referenced in this rule have not been revised to account for the EPA's AQI update."

Same PM2.5 levels, EPA's 2024 AQI numbers⁸

"Previous AQI values"	"New AQI values (effective May 2024)"
"101 - 250"	"101 - 276"
"251 - 500"	"277 - 848"
"501 and above"	"849 and above"

Oregon OSHA's fact sheet: "In May 2024, the U.S. Environmental Protection Agency (EPA) updated how it calculates and reports Air Quality Index (AQI) values. The requirements based on PM2.5 concentrations in the Oregon OSHA wildfire smoke rules are not changing."⁸

Washington

Wildfire Smoke, Department of Labor & Industries⁹

From L&I's summary table of its rule (Chapter 296-820 WAC), by NowCast AQI for PM2.5. Each level adds to the levels before it; the table lists more at some levels.

AQI 0 to 71: "Prepare a written wildfire smoke response plan." "Provide wildfire smoke training to employees."
AQI 72 to 100: "Ensure only trained employees work outdoors."
AQI 101 to 350: "Implement exposure controls." "Make N95 respirators available for voluntary use."
AQI 351 to 848: "Directly distribute N95 respirators to employees for voluntary use."
AQI 849 to 956: "Implement a complete required use respiratory protection program, including fit-testing, medical evaluations, requiring employees to be clean-shaven, and requiring the use of particulate respirators."
AQI 957 or more: "Require respirators with an assigned protection factor (APF) of 25 or more."

Help in your state

California: Clean Air Centers map, California Air Resources Board. "Clean Air Centers provide a safe place for Californians to go during periods of intense wildfire smoke or poor air quality." Checked October 4, 2026.
Colorado: HEPA Air Purifier Program (Lafayette), City of Lafayette. "When summer brings high ozone days and wildfire smoke, clean indoor air matters. That’s why the City is proud to bring back the HEPA Air Purifier Program, helping neighbors breathe easier when outdoor air quality declines." Checked October 4, 2026.
Minnesota: Free N95 and N99 masks (Cook County), Cook County Public Health and Human Services. "Free N95/N99 masks are available to community members in limited quantity at the front desk of Cook County Public Health and Human Services while supplies last." Checked October 4, 2026.
Montana: Clean air centers for the 2026 smoke season, Montana Department of Public Health and Human Services. "In 2026, MT DPHHS is working with local partners in Flathead County, Lincoln County, Blackfeet Reservation, and the Flathead Reservation." Checked October 4, 2026.
Oregon: Cleaner air shelters, Oregon Department of Human Services. "Cleaner air shelters during wildfire smoke and other poor air quality events" Checked October 4, 2026.
Oregon: Free air purifiers for high-risk wildfire zones, Oregon Health Authority. "With $4.7 million, Oregon has purchased 5,000 new home air purifiers." Checked October 4, 2026.

A monitor for the air inside

Airthings View Plus: $329.99
Price checked October 1, 2026

Airthings says:¹⁰

"PM2.5 is fine particulate matter small enough to reach deep into the lungs."
"Typical sources include wildfire smoke, gas cooking, and candles."

Check price at Airthings