The scale of the wildfires burning across the West Coast is unprecedented. To date, more than 3 million acres have burned in California and 12 people have died… and wildfire season has just begun. The smoke in San Francisco is so thick that it blocked out the sun, creating apocalyptic landscapes.

While hundreds of thousands of people have been ordered to evacuate, those who remain in their homes have been told to stay indoors as much as possible. But, is staying indoors enough to keep people safe from the smoke?

Why Wildfire Smoke Is Dangerous

While all smoke can cause health problems, wildfire smoke is particularly dangerous because of the toxic mix of pollutants it carries.  What exactly is in the smoke depends on a few things:

  • what’s burning
  • the temperature
  • the distance between the person breathing the smoke and the fire producing it.

As the fires tear through towns, homes, and forests, they pick up a variety of pollutants including carbon monoxide, volatile organic compounds (VOCs), carbon dioxide, hydrocarbons, and nitrogen oxides. It’s the tiniest of these particles, known as PM2.5, that are the most dangerous.

How far can smoke travel?

While the bigger particles often fall to the ground near the site of the wildfire in the form of ash, those tiny PM2.5 particles travel much farther, sometimes even reaching across continents. Because the smallest particles are the most dangerous, it’s important for people even hundreds of miles away to know how to protect themselves from the dangers of wildfire smoke.

Am I safe indoors? 

While staying indoors is definitely the best option during a wildfire (unless you’re in an evacuation area), wildfire smoke can enter your home in several ways:

  • through open windows and doors, which is known as natural ventilation.
  • through mechanical ventilation devices such as bathroom or kitchen fans that vent to the outdoors, or heating, ventilation, and air conditioning (HVAC) systems with a fresh air intake.
  • through small openings, joints, cracks, and around closed windows and doors through a process called infiltration.

What can I do to keep my indoor air clean?

Monitor Local Smoke Warnings

Even if you think that your home is far enough away from the wildfires to be of concern, it’s always important to check your local air quality and pay attention to any smoke warnings on the local news.  provides free air quality monitoring each day.

Keep windows and doors closed

Most of the time indoor air actually contains two to five times more pollutants than outdoor air.  But, during a wildfire, the situation changes. Keeping windows and doors shut tightly can minimize the smoke that enters your home. It also helps to limit the number of times you enter and exit your home.

Use the right air conditioner

Unfortunately, the wildfires have coincided with a blistering heatwave.  AC’s can be useful in both keeping your home cool and lowering indoor smoke.  When running an AC, make sure the filter is clean and that any “fresh air” settings that bring in air from the outdoors are disabled. Don’t use ACs that rely on outdoor air.

Avoid activities that cause more indoor pollution including:

  • Smoking cigarettes.
  • Using gas, propane, or wood-burning stoves and furnaces.
  • Spraying aerosol products.
  • Frying or broiling food.
  • Burning candles or incense.
  • Vacuuming, unless you use a vacuum with a HEPA filter.

Purchase an air purifier with a True HEPA filter.

The particles in wildfire smoke are generally between 0.4 and 0.7 microns. True-HEPA air filters are exceptionally good at removing particles of that size from the air. In fact, the EPA recommends that residents in areas vulnerable to wildfires purchase an air purifier before a fire emergency occurs. Because wildfire smoke is made up of many different hazardous pollutants, be sure to look for high-quality air purifiers that are equipped to deal with gasses and volatile organic compounds (VOCs).

Use caution when cleaning up after the fire.

While you may be anxious to get your home back together after a fire, keep in mind that debris can continue to smolder and release airborne pollutants days after the fire. Wait until the debris has fully died down and then be sure to wear protective clothing and masks when cleaning up.