Wildfire Smoke: A Practical Survival Guide

On September 9, 2020, the skies over San Francisco turned orange. By noon, AQI readings across the Bay Area were above 200. Hospitals reported spikes in emergency visits. Sales of N95 respirators sold out within hours.

It wasn't a freak event. It was a preview.

Wildfire smoke is now a recurring public health emergency across the American West — and increasingly the Midwest, South, and Northeast as fire seasons lengthen and intensify. For the 130 million Americans who live in areas with regular smoke exposure, understanding what's actually in that haze, and how to protect yourself from it, has become a basic life skill.

What makes wildfire smoke different from ordinary air pollution is its intensity and chemistry. Urban PM2.5 — from traffic and industry — is bad enough. Wildfire smoke is a concentrated cocktail of fine particles, carbon monoxide, nitrogen oxides, volatile organic compounds, and dozens of toxic compounds released from burning vegetation, homes, and everything in them. A 2016 critical review in Environmental Health Perspectives found evidence that wildfire PM2.5 may be more toxic per microgram than urban PM2.5 — meaning the same AQI number from smoke is potentially more damaging than the same number from traffic.

The people most at risk are the ones you'd expect: those with asthma, heart disease, COPD, or compromised immune systems. But healthy adults are not immune. Repeated smoke exposures accumulate, and the evidence from wildland firefighters — who face the most concentrated occupational smoke exposure — shows elevated rates of lung cancer and cardiovascular mortality over careers.

When smoke moves in, the outdoors becomes an exposure source. The goal is to make your indoor environment meaningfully cleaner than outside — which is achievable even without expensive equipment.

Seal what you can. Close windows and doors. Turn off fans that pull outdoor air in. If you have a forced-air HVAC system, switch it to recirculate mode — this prevents it from drawing smoky outdoor air inside while still filtering and moving interior air.

Filter aggressively. • A HEPA air purifier in your main living space and bedroom is the single most effective indoor protection. Run it on high during smoke events. • If you don't have a purifier, a DIY box fan filter — a furnace filter (MERV 13 or higher) taped to the back of a box fan — can reduce indoor PM2.5 significantly for under $30. • Replace HVAC filters after a major smoke event; they become saturated quickly.

Reduce indoor sources during smoke events. Cooking, candles, vacuuming, and anything that generates particles indoors adds to your exposure when air exchange with outdoors is cut off. Keep indoor sources minimal when you're managing a smoke event.

Create a clean room. If you can't filter your whole home, pick one room — ideally a bedroom — and concentrate your filtration there. Spending your sleeping hours in cleaner air provides significant recovery time for your lungs.

Not all masks are created equal, and the wrong mask during a smoke event provides a false sense of security without meaningful protection.

What works: • N95 respirators filter at least 95% of airborne particles, including the fine particles in wildfire smoke. They must be fitted properly — pressed against the face with no gaps — to work. Beards prevent an adequate seal. • KN95 masks (the Chinese equivalent standard) offer similar filtration when properly fitted, though quality varies more by manufacturer. • P100 respirators (the half-face or full-face industrial type) offer even higher protection, appropriate for extended outdoor work during heavy smoke.

What doesn't work: • Surgical masks and cloth masks are not rated for fine particle filtration. They stop large droplets but don't protect against wildfire smoke particles, which are in the PM2.5 range. • Single-layer gaiters and bandanas provide essentially no protection against PM2.5.

Fit matters more than rating. An N95 with a poor seal performs worse than the package suggests. When putting on an N95, press the metal nose strip firmly against your nose bridge and perform a quick seal check — breathe in sharply and the mask should collapse slightly against your face. If air leaks around the edges, adjust.

For most smoke events, an N95 worn outdoors for short periods — walking to a car, brief errands — is appropriate. For extended outdoor activity during heavy smoke, stay inside.

One of the hardest judgment calls during wildfire season is when the situation has moved beyond air quality management into safety territory.

AQI thresholds as a guide: • Under 150: Most healthy adults can be outside briefly. Sensitive groups should limit time outdoors. • 150–200 (Red): Limit all outdoor activity. Keep windows closed. Run filtration. • 200–300 (Purple): Stay indoors. This is not a "take a short walk" situation. Outdoor exercise is not advisable for anyone. • Above 300 (Maroon): Treat it as a health emergency. If you have respiratory or cardiac conditions, consider whether staying in the area makes sense.

When to consider leaving: Air quality alone rarely justifies evacuation — that decision is made by emergency managers based on fire proximity and spread. But if you have severe asthma, heart failure, or another condition that makes even indoor smoke exposure dangerous, and you have somewhere to go, going is a legitimate choice.

Watch for symptoms. Chest tightness, shortness of breath, headache, and eye irritation are common with moderate smoke exposure and typically resolve when you get to clean air. Worsening symptoms — difficulty breathing, chest pain, or symptoms that don't improve indoors — warrant medical attention.

After the smoke clears: Open windows and ventilate thoroughly. Replace HVAC filters. Wipe down surfaces where ash has settled. Smoke particles can linger on surfaces and in dust long after the air has cleared.