Wildfire smoke — when your AQI hits 150, what you should do in the next hour and the next 48 hours
Western US wildfire smoke now affects households 500-1500 miles from the fire itself. Air Quality Index numbers translate into specific household actions at four escalating thresholds. Most households reach for an N95 only at AQI 200+; they should be acting at 100.
The AQI scale that matters for households
The US Environmental Protection Agency Air Quality Index (AQI) translates particulate-matter pollution into a numerical scale. For wildfire smoke (PM2.5 dominated), the breakpoints that matter for households are:
- 0-50 (Green) — Good: No action needed.
- 51-100 (Yellow) — Moderate: Sensitive groups (asthma, heart conditions, elderly, infants) reduce prolonged outdoor exertion. No action for healthy adults.
- 101-150 (Orange) — Unhealthy for Sensitive Groups: This is the threshold most households underestimate. Sensitive groups should stay indoors with windows closed. Healthy adults reduce prolonged outdoor exertion. N95 masks become useful if going outside.
- 151-200 (Red) — Unhealthy: Everyone reduces outdoor activity. N95 masks for any outdoor time. Indoor air filtration becomes meaningful.
- 201-300 (Purple) — Very Unhealthy: Avoid outdoor activity entirely. N95 mandatory if must go outside. Windows sealed; HVAC on recirculate.
- 301+ (Maroon) — Hazardous: All groups stay indoors. Skin contact with outdoor air becomes a real health risk for sensitive groups.
The Western US during August now routinely sees AQI 100-200 days across multiple states simultaneously. Smoke from California and Oregon fires regularly reaches Colorado, Utah, and even the Midwest at concentrations meaningful for sensitive groups.
What to do in the next hour when AQI hits 150
- Close every window and door. Even cracks matter — wildfire smoke particulate is small (PM2.5 = 2.5 micrometers or less). Seal weatherstripping gaps with damp towels if you have them.
- Set HVAC to recirculate mode. Most thermostats have an "indoor recirculation" or "fan-only recirculate" mode. Switch to it; this prevents drawing outdoor smoke through your AC system. If your HVAC has a MERV 13 or higher filter, leave it running. If MERV 8 or lower, change it now (HEPA equivalent) or run a separate air purifier in the room you spend most time in.
- Identify your "clean room." One room in your home, typically smaller with fewer doors and windows. Close the door, run an air purifier (HEPA filter, CADR rating above 200 for an average bedroom). This is where sensitive household members spend the next 24-48 hours.
- Verify your N95 supply. Surgical masks do NOT filter wildfire smoke effectively. You need actual N95 or KN95 respirators. Most US households should have a box of 10-20 N95s for situations like this; if you don't, buy them today (most pharmacies + Amazon next-day).
- Check on the most vulnerable person in your household. Asthma sufferer, heart condition, elderly, infant. Their breathing should be unaffected at this level if they stayed indoors. If breathing has noticeably changed, prepare for medical contact.
What to do in the next 48 hours
- Monitor AQI on the EPA AirNow.gov dashboard. Updated hourly. Bookmark your specific monitoring station. Note the trend — improving, stable, worsening. Decision to shelter or leave the region depends on trajectory, not single-hour reading.
- Limit time outdoors to essential trips only. Quick grocery run: yes, with N95. Walking the dog: yes, short loops, with N95 if AQI > 150. Outdoor exercise: postpone.
- Stay hydrated. Air pollution stress on the body increases water requirements. Drink more than feels necessary.
- Avoid creating indoor pollution. No candles, no fireplaces, no aerosols. Frying / sauteing: postpone if possible. Vacuum cleaning stirs up settled particulate.
- Monitor your symptoms and family symptoms. Persistent cough that wasn't there before, headache that lingers, eye irritation, breathing difficulty — these are real responses to smoke exposure, not panic. Note them; tell your doctor if persistent.
- Plan for potential extended exposure. If AQI stays above 150 for 5+ days, your "clean room" plan becomes a 7-day plan. Stock food, medications, water for that duration without leaving.
Indoor air purifier guidance
If you do not own one and are buying one this week:
- HEPA filter rated H13 or higher
- CADR (Clean Air Delivery Rate) of at least 200 cfm for a typical bedroom
- Brand reliability matters: Coway, Levoit, Honeywell, Winix are reliable; off-brand units often underperform their ratings
- Cost: $80-300 for a unit appropriate for a 200 sq ft bedroom
A single air purifier in your designated clean room reduces PM2.5 by 70-85% within 30-60 minutes. Most homes can survive a multi-day smoke event in good health with one purifier and disciplined room-use.
What this is not
This is not a panic about wildfire smoke. The vast majority of smoke events end with mild discomfort and resume normal life within 1-3 days. The point of the AQI thresholds above is that the household that acts at 150 lives through it without medical incident. The household that waits to act until AQI 250 may not.
The single highest-leverage action is the clean room + air purifier setup. Total cost: $100-300 one-time. Pays off across every smoke event in coming years.
One thing this week: check current AQI for your area at AirNow.gov. Note today's reading. Bookmark for future monitoring.
— Systems Fail Lab