The most effective way to stay safe from wildfire smoke is to limit your exposure: stay indoors with filtered air, wear a proper respirator when you must go outside, and track air quality so you know when conditions are dangerous. Wildfire smoke contains fine particles small enough to pass through your lungs and into your bloodstream, where they can trigger heart attacks, strokes, and severe breathing problems within hours of exposure.
Why Wildfire Smoke Is Dangerous
Wildfire smoke is filled with fine particulate matter, tiny particles less than 2.5 micrometers across. For reference, that’s about 30 times smaller than the width of a human hair. These particles are small enough to reach the deepest parts of your lungs and cross into your bloodstream, which is what makes wildfire smoke more harmful than it might seem from the outside.
Short-term exposure over just a few hours to weeks can trigger heart attacks, arrhythmias, heart failure, and stroke, particularly in people with existing heart disease. Longer-term exposure during extended fire seasons is linked to increased cardiovascular death and decreased life expectancy. Even healthy people can develop coughing, throat irritation, headaches, and shortness of breath when air quality deteriorates.
Check Air Quality Before Going Outside
The EPA’s Air Quality Index (AQI) is the standard tool for knowing when smoke levels are dangerous. AQI is measured on a scale from 0 to 500, and the thresholds that matter most are:
- 101 to 150 (Orange): Unhealthy for sensitive groups. Children, older adults, pregnant women, and people with heart or lung conditions should reduce outdoor time.
- 151 to 200 (Red): Unhealthy for everyone. Some healthy adults will notice symptoms. Limit prolonged outdoor exertion.
- 201 to 300 (Purple): Very unhealthy. Health risks increase for the entire population. Avoid outdoor activity.
- 301+ (Maroon): Hazardous, emergency-level conditions. Everyone should stay indoors.
The best real-time resource is AirNow’s Fire and Smoke Map at fire.airnow.gov. It combines data from permanent government monitors, temporary monitors set up during fire events, and consumer-grade air sensors from networks like PurpleAir and Clarity. It also overlays NOAA satellite-detected smoke plumes so you can see where smoke is moving, though those plumes are most accurate in the afternoon and aren’t visible through clouds or at night. Bookmark this site before fire season starts. AQI can change rapidly as wind shifts, so check it multiple times a day during active fires.
Keep Indoor Air Clean
Staying indoors only helps if you’re actually keeping smoke out and filtering the air inside. Start by closing all windows and doors. Seal gaps under doors with towels, or better yet, install weatherstripping around doors and windows where you notice drafts. Even small cracks can let in enough smoke to raise indoor particle levels significantly. Tightening up your home this way also saves energy, so the investment pays off year-round.
If you have central air conditioning, run it on recirculate mode so it’s not pulling in outdoor air. Upgrade your HVAC filter to at least MERV 13, which is the minimum rating effective against wildfire smoke particles. The average particle size in wildfire smoke is 0.3 micrometers, which happens to be the hardest particle size for filters to capture, so lower-rated filters will let most of the harmful particles through.
A portable HEPA air purifier is one of the best investments you can make. Run it in the room where you spend the most time with the door closed to create a “clean room.” If you don’t have a purifier and can’t get one during a smoke event, you can build an effective DIY alternative called a Corsi-Rosenthal box. You need a standard 20-by-20-inch box fan, four 20-by-20-by-2-inch MERV 13 furnace filters, and duct tape. Tape the four filters into a cube shape with the airflow arrows pointing inward, attach the fan on top blowing outward, and seal the bottom with cardboard from the fan’s box. Testing at UC Davis found that on the lowest fan setting, these boxes perform comparably to commercial HEPA air cleaners.
One critical point: do not use regular vacuums or shop vacuums to clean up indoor dust during smoke events. They lack fine-particle filtration and will blow tiny particles back into the air through their exhaust. Only HEPA-filter vacuums are safe to use.
Wear the Right Mask Outdoors
When you need to go outside during a smoke event, a well-fitting N95 respirator filters out 95% of airborne particles. A P100 respirator filters at least 99.97%. The “P” designation also means it’s oil-resistant, which can matter when smoke contains oily compounds from burned structures, but for most people an N95 is effective and easier to find.
Fit matters as much as the filter rating. The mask should seal tightly around your nose and chin with no gaps at the edges. If air leaks in around the sides, the filtration rating is meaningless. Cloth masks, bandanas, and surgical masks do not filter wildfire smoke particles effectively. They may reduce some larger particles but will not stop the fine particulate matter that causes the most damage.
If you have facial hair, it will prevent a proper seal. Shaving the area where the mask contacts your skin is the only way to get reliable protection from a respirator.
Who Faces the Highest Risk
Certain groups need to take extra precautions and should start limiting exposure at lower AQI thresholds.
Children up to age 18 are especially vulnerable because their lungs are still developing. They also tend to spend more time outdoors and breathe more air per pound of body weight than adults, which increases the dose of smoke they actually take in. Symptoms in children include coughing, wheezing, chest tightness, and reduced lung function. Kids with asthma are at particular risk for attacks.
Pregnant women breathe at a higher rate, which increases smoke exposure. There is evidence linking smoke exposure during pregnancy to gestational diabetes, high blood pressure, low birth weight, and preterm birth. The fetus itself may be more sensitive to the effects of smoke.
People with asthma, COPD, or other lung diseases can experience severe breathing crises from smoke exposure, including emergency-level episodes of coughing, wheezing, and chest tightness. People with cardiovascular disease, diabetes, or obesity face elevated risk of heart attacks and strokes during smoke events. For all of these groups, the goal should be near-zero outdoor exposure when AQI rises above 100.
Cleaning Up Ash Safely
After a fire, ash settled on surfaces can be just as hazardous as airborne smoke if you disturb it incorrectly. The most important rule: never use a leaf blower, and never dry-sweep aggressively. Both actions launch fine particles back into the air where you’ll inhale them.
For most surfaces, gentle sweeping followed by wet mopping works best. Lightly dusted areas may only need a damp cloth. If you need to wet down heavier ash deposits, use as little water as possible to avoid creating runoff that carries contaminants into storm drains. Wear an N95 respirator during cleanup, and keep children away from the area entirely.
If you’re cleaning indoors, only use a vacuum with a HEPA filter. Standard vacuums and shop vacuums will recirculate the smallest, most dangerous particles right back into your living space.