How do you protect your lungs from wildfire smoke?

Short answer. The most effective protection is to limit your time outdoors when smoke is in the air, according to the U.S. EPA ¹. Indoors, close one room off from outside air and run a portable air cleaner that does not produce ozone ⁹³. If you must go out, wear a well-fitted NIOSH-approved N95 or P100 respirator ¹; it filters fine particles but not the gases in smoke ⁶.

Why is wildfire smoke hard on the lungs?

Wildfire smoke can make anyone sick ⁵. The U.S. CDC lists coughing, trouble breathing, wheezing, asthma attacks, eye and throat irritation, headaches, tiredness, chest pain and a fast heartbeat among the effects of breathing it ⁵.

Some people face higher risk: people with asthma, COPD, heart disease, diabetes or chronic kidney disease, pregnant people, children and responders ⁵. Canada's Air Quality Health Index also treats children, adults over 65 and people with health conditions as at-risk groups ⁸. Plan for these people first.

How do you know when the air is dangerous?

Check your local index before deciding to go out. The United States and Canada use different scales, so a number from one country cannot be read on the other's scale.

United States: Air Quality Index (AQI), on AirNow ⁴

Canada: Air Quality Health Index (AQHI) ⁸

A practical reading of both tables: at-risk people should start acting at the middle of the scale (AQI above 100 in the U.S. ⁴, AQHI 4–6 in Canada ⁸), and everyone should be acting by the upper categories.

How do you set up a clean-air room?

The EPA describes a "clean room" as the place to wait out heavy smoke ⁹. Its steps ⁹:

• Pick a room that is comfortable and big enough for everyone; a bedroom with an attached bathroom works well.
• Close all windows and doors in the room, without making it hard to get out.
• Stay cool with fans or air conditioning; if the system brings in fresh air, set it to recirculate or close the intake.
• Run a portable air cleaner that does not produce ozone, continuously and on the highest fan setting if you can.
• Do not create smoke or particles inside: no smoking, vaping, candles, incense, frying or broiling.
• Spend as much time as possible in that room.

Which portable air cleaner actually helps?

Size matters more than brand. The EPA says to choose a unit whose clean air delivery rate (CADR) is large enough for the room ³. Its sizing chart gives minimum CADRs, in cubic feet per minute, for rooms with an 8-foot ceiling ³:

Health Canada gives a similar rule of thumb: the tobacco-smoke CADR should be at least two-thirds of the room's area, and higher ceilings need more ⁷. Health Canada advises choosing the highest tobacco-smoke CADR your budget allows, because higher values remove more fine particles ⁷.

Both agencies note that portable cleaners often reach a high CADR by using a HEPA filter ³⁷. Both say to avoid devices that produce ozone ³⁷, which the EPA describes as a lung irritant ³. The EPA lists some devices using ionizers, electrostatic precipitators, uncoated UV lamps or plasma technology as devices that may emit ozone, and states that no federal agency has approved ozone generators for occupied spaces ³.

Place the unit where people spend the most time and run it as often as possible on the highest fan speed ². Health Canada adds that higher fan speeds and longer run times filter more air ⁷.

If you cannot buy a rated unit. The EPA describes a do-it-yourself cleaner made by attaching one or more furnace filters to a box fan, but says commercial cleaners with a known CADR are typically preferred ².

If you have central air. Use a high-efficiency filter such as MERV 13, or the highest rating your system can take; make sure it fits snugly without bending it, set the fan to "On" rather than "Auto", and change filters more often during heavy smoke ². For changes to ducts or the system itself, ask a qualified HVAC technician.

What should you stop doing indoors during smoke?

The EPA's list of things to avoid indoors during a smoke event ²:

• smoking or vaping;
• gas, propane or wood-burning stoves and furnaces;
• aerosol sprays;
• frying or broiling food;
• candles or incense;
• vacuuming, unless the vacuum has a HEPA filter;
• strenuous activity, which makes you inhale more smoke;
• a window air conditioner whose outdoor air damper cannot be closed.

After the smoke clears, do not dry-sweep ash: mist hard surfaces with water first, then wet-mop ².

How do you wear a respirator correctly?

A respirator only works if it seals. The EPA says to pick a NIOSH-approved particulate respirator labelled N95 or P100, sized to fit over the nose and under the chin and seal tightly, and to check the seal using the package instructions ¹. The skin must be clean-shaven where the respirator touches the face, because a good seal is not possible with facial hair ¹. The Public Health Agency of Canada also says facial hair prevents a tight fit ⁶.

The Public Health Agency of Canada accepts NIOSH-certified N95 respirators or equivalents such as KN95 and KF94 ⁶. It says cloth, medical and surgical masks do not fit the face well and their materials may not be effective filters against wildfire smoke ⁶.

Replace the respirator when it is dirty, damp or damaged, and do not wear one while sleeping ⁶. People with heart, lung or other health conditions may find respirators hard to tolerate; the agency's advice is to listen to your body ⁶.

What a respirator does not do. It reduces exposure to fine particles but does not protect against the gases in smoke ⁶. The EPA ranks limiting time outdoors as the most effective protection and presents the respirator for when you have to go out ¹.

What official agencies recommend

• United States (EPA, AirNow, CDC). Limit time outdoors first; reduce physical activity and use portable air cleaners indoors ¹. Use a fitted N95 or P100 if you must be exposed ¹. Follow the AQI categories on AirNow ⁴.
• Canada (Public Health Agency of Canada, Health Canada, Environment and Climate Change Canada). Use a well-fitting N95 or equivalent (KN95, KF94) if you must spend time outdoors ⁶. Size air cleaners by tobacco-smoke CADR, at least two-thirds of the room area ⁷. Follow AQHI messages, which differ for at-risk people and the general population ⁸.

Where they differ:

• Scale. The U.S. AQI runs from 0 to over 300 with six categories ⁴; Canada's AQHI runs from 1 to 10+ with four risk levels ⁸.
• Ear loops. The EPA warns against respirators with a single strap or two straps that go around the ears ¹; the Public Health Agency of Canada tells users to adjust "the bands or ear loops" for a snug fit ⁶. A head-strap model meets both.
• Young children. The EPA and the Public Health Agency of Canada both set the floor at age 2 ¹⁶. The EPA adds that NIOSH-approved respirators do not come in sizes suitable for young children, and that adults should watch children wearing one ¹. A clean-air room does not depend on fit, so it suits small children best.

Frequently asked questions

Does a surgical or cloth mask protect against wildfire smoke?

Not reliably. The Public Health Agency of Canada says these masks do not fit the face well and their materials may not filter wildfire smoke effectively ⁶. The EPA recommends a NIOSH-approved N95 or P100 particulate respirator instead ¹.

Can children wear an N95?

From age 2, according to the EPA and the Public Health Agency of Canada ¹⁶. The EPA notes that approved respirators are not made in sizes for young children, so a proper fit may be hard to get ¹. A clean-air room protects them without depending on fit ⁹.

How big an air purifier do I need?

For a room with an 8-foot ceiling, the EPA chart calls for a CADR of about 65 cfm per 100 square feet, for example 195 cfm for 300 square feet ³. Health Canada expresses it as a tobacco-smoke CADR of at least two-thirds of the room's area ⁷.

Should I open windows once it cools down?

Not while smoke is outside: the EPA's clean-room steps include closing windows and doors ⁹. The EPA does suggest using times when outdoor air quality improves, even briefly, to open windows and air out the house ².

At what AQI should I stay inside?

Sensitive groups may have health effects from AQI 101 ⁴, and at 201 and above the risk is increased for everyone ⁴. In Canada, at-risk people should avoid strenuous outdoor activity at AQHI 10+ ⁸. Check your local index each day during a smoke event.

Have the gear before the smoke arrives

The EPA's first advice is to limit time outdoors when there is smoke ¹. A clean room is quicker to set up when the air cleaner, spare filters and respirators are already at home; compare any kit you buy with the agency guidance above.

Sources

1. U.S. Environmental Protection Agency (EPA) — Protect Yourself From Wildfire Smoke and Ash — https://www.epa.gov/wildfires/protect-yourself-wildfire-smoke-and-ash (accessed 2026-10-20)
2. U.S. Environmental Protection Agency (EPA) — Wildfires and Indoor Air Quality (IAQ) — https://www.epa.gov/indoor-air-quality-iaq/wildfires-and-indoor-air-quality-iaq (accessed 2026-10-20)
3. U.S. Environmental Protection Agency (EPA) — Guide to Air Cleaners in the Home — https://www.epa.gov/indoor-air-quality-iaq/guide-air-cleaners-home (accessed 2026-10-20)
4. AirNow (U.S. EPA and partner agencies) — AQI Basics — https://www.airnow.gov/aqi/aqi-basics/ (accessed 2026-10-20)
5. Centers for Disease Control and Prevention (CDC) — How Wildfire Smoke Affects Your Body — https://www.cdc.gov/wildfires/risk-factors/index.html (accessed 2026-10-20)
6. Public Health Agency of Canada — Using a respirator mask during wildfire smoke events — https://www.canada.ca/en/public-health/services/publications/healthy-living/using-respirator-mask-during-wildfire-smoke-events.html (accessed 2026-10-20)
7. Health Canada — Using a portable air cleaner to improve indoor air — https://www.canada.ca/en/health-canada/services/publications/healthy-living/using-portable-air-cleaner-wildfire-smoke.html (accessed 2026-10-20)
8. Environment and Climate Change Canada — About the Air Quality Health Index — https://www.canada.ca/en/environment-climate-change/services/air-quality-health-index/about.html (accessed 2026-10-20)
9. U.S. Environmental Protection Agency (EPA) — Create a Clean Room to Protect Indoor Air Quality During a Wildfire — https://www.epa.gov/indoor-air-quality-iaq/create-clean-room-protect-indoor-air-quality-during-wildfire (accessed 2026-10-20)