What to Do When Wildfire Smoke Makes the Air Unsafe

Residential street shrouded in thick orange wildfire smoke haze

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Quick answer: Check your local Air Quality Index (AQI) at airnow.gov, stay indoors with windows and doors closed once AQI passes 150 (“Unhealthy”), run a HEPA air purifier or a DIY box-fan filter, and wear a properly fitted N95 (not a cloth or surgical mask) if you must go outside.

Understand the AQI Scale

AQI Category What to do
0-50 Good No action needed
51-100 Moderate Sensitive groups reduce prolonged outdoor exertion
101-150 Unhealthy for Sensitive Groups Kids, elderly, asthma/heart patients limit outdoor time
151-200 Unhealthy Everyone limits outdoor exertion; close windows
201+ Very Unhealthy / Hazardous Stay indoors, run filtration, avoid all outdoor activity

Seal and Filter Your Indoor Air

  • Close all windows, doors, and the fireplace damper.
  • Set HVAC to recirculate (not fresh-air intake) and use a MERV 13+ filter if your system supports it.
  • Run a portable HEPA air purifier in the room(s) you spend the most time in — bedrooms first.
  • No purifier? Build a Corsi-Rosenthal box: a box fan taped to 4 MERV-13 furnace filters — a well-documented, effective low-cost DIY option.
Gear that helps here:

If You Must Go Outside

A properly fitted N95 or P100 respirator blocks the fine particulate matter (PM2.5) that makes wildfire smoke dangerous — cloth masks and surgical masks do not filter these particles effectively. Limit time outside, avoid exertion, and reschedule outdoor exercise entirely on Unhealthy+ days.

Common Mistakes

  • Relying on a cloth or surgical mask, which doesn’t filter PM2.5 smoke particles.
  • Opening windows to ‘air out’ the house during a smoke event — this brings in more particulates than it removes.
  • Running a fresh-air-intake HVAC setting instead of recirculate mode.
  • Ignoring symptoms like chest tightness, coughing, or headache and continuing normal outdoor activity.

    • Frequently Asked Questions

    Do regular window AC units filter out smoke?

    No — most window units aren’t designed to filter fine particulates and may pull in outdoor smoke. A dedicated HEPA purifier is needed for real filtration.

    How long does wildfire smoke typically linger in an area?

    It varies with wind and fire behavior — anywhere from a day to over a week during sustained fire activity, which is why checking AQI daily (not just once) matters.

    Are pets affected by wildfire smoke too?

    Yes — keep pets indoors during poor air quality days and watch for coughing, wheezing, or lethargy, especially in short-nosed breeds.

    Is it safe to exercise outside if AQI is ‘Moderate’?

    Generally yes for healthy adults, but sensitive groups (asthma, heart conditions, children, elderly) should still reduce prolonged exertion even at Moderate levels.