Staying indoors is one of the best ways to protect yourself from the potentially harmful effects of wildfire smoke. Reduced exposure to smoke can protect your lungs, heart, eyes, nose, throat and immune system.
However, smoke can enter homes and contaminate indoor air. The impact on indoor air quality (IAQ) varies, depending on smoke density and how close your home is to the fire.
Why is smoke harmful?
Smoke from burning homes, commercial buildings, trucks, automobiles and gas stations contains harmful gases, chemicals and fine particulate matter. The risk increases when these substances merge with forest fire smoke.
Air-quality alerts, such as the Air Quality Index (AQI), focus on six main components: nitrogen dioxide, sulfur dioxide, ozone, carbon monoxide, lead and particulate matter (PM2.5 and PM10).
In a wildfire, the major contributor to smoke is fine particulate matter. Of particular concern are the smallest particles, known as PM2.5. These particles are invisible to the eye. Because they are so small, they can travel deeply into the lungs and be absorbed into the body.
Larger particles, called PM10, are trapped high up in the lungs and typically can be coughed out. However, they can still cause irritation.
Who is at risk?
At-risk populations sensitive to wildfire smoke exposure include:
- Children younger than 18
- Adults age 65 years or older
- Pregnant women
- People with chronic health conditions such as heart or lung disease, asthma or diabetes
- Anyone who is seriously ill
- Outdoor workers
- People of low socioeconomic status, including those who are homeless and those who have limited access to medical care
As the AQI rating increases, however, anyone can experience serious complications. Seek advice from a medical professional if conditions persist.
Respiratory symptoms such as dry cough, sore throat and difficulty breathing are common to both COVID-19 and wildfire smoke exposure. People with compromised immune systems and those currently or previously infected with COVID-19 are at increased risk from wildfire smoke.
How does smoke enter homes?
There are several ways outdoor air can enter your home. These include:
- Open windows and doors
- Devices such as bathroom or kitchen fans that vent to the outdoors
- Heating, ventilation and air conditioning (HVAC) systems with a fresh air intake
- Small openings, joints and cracks, as well as around closed windows and doors
Monitor fires and air quality
If there is an active fire in your area, follow recommendations from your local emergency manager. Emergency managers may make information available via local news outlets, web pages or automatic notification systems. Conditions can change quickly, so be prepared to evacuate if necessary.
Assume that homes in Level 3 Evacuation Zones are heavily contaminated. Follow local emergency management instructions before reentering. Personal protective equipment or commercial cleaning may be required.
Wear a mask
If you must leave the house, remember to practice 6-feet physical distancing and wear a mask. Cloth masks can provide some protection from COVID-19, but they won't protect you from wildfire smoke.
For protection from smoke, look for respirators (masks) marked NIOSH with N95 or P100. These can be found online or in drugstores, hardware or home repair stores. If the mask has vents, tape them shut or place a cloth mask over them.
Frontline health-care workers use these higher quality masks, so they may be in short supply during the pandemic.
Improve indoor air quality
When the Air Quality Index indicates that smoke levels are unhealthy, take steps to protect the indoor air quality in your home and stay inside.
Keep smoke out of your home
Close windows and doors, but don’t block or tamper with exits. Minimize use of exhaust fans or range hoods. If your window air conditioner or HVAC system has a fresh air option, turn it off or close the intake.
When someone returns home after prolonged exposure to wildfire smoke, they should consider wiping shoes or boots on a wet towel before entering the home. Set up a plan so they can carefully remove and bag all clothing and take a shower before dressing. Launder clothing immediately or as soon as practical.
Avoid activities that create smoke or other air-borne particles
- Smoking cigarettes, pipes and cigars
- 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 High Efficiency Particulate Air (HEPA) filter
Dust or mop surfaces with a damp cloth as needed to keep settled particles from getting back into the air.
Set up a clean room
Without a central HVAC system or multiple portable air cleaners, it can be hard to improve air quality in the entire house. In this case, focus on setting up a clean room. The clean room should be big enough that everyone in your household is comfortable spending time there.
Start with the simple no-cost steps outlined above. The following options will provide additional benefits:
- Purchasing a portable air cleaner with HEPA filter
- Upgrading your HVAC system with best-quality high-efficiency filters
- Making a low-cost portable air cleaner
Commercial air filters
During a wildfire smoke event, commercial portable air cleaners fitted with high-efficiency filters may reduce indoor particle concentrations by as much as 45%. Both people and pets will benefit from improved indoor air quality while you wait for wildfire smoke to clear.
Use an air cleaner that is the right size for the room. Use high-efficiency HEPA air-cleaning filters, if available. Avoid using an air cleaner that works by generating ozone, which will increase the pollution in your home.
Place the air cleaner where people spend the most time, such as a bedroom. This may be particularly helpful to a person with asthma or chronic obstructive pulmonary disease (COPD). For retired or homebound individuals, place the portable room air cleaner in the room that is used the most.
To maximize air cleaner effectiveness:
- Operate it continuously, or as often as possible.
- Use the highest fan speed and make sure the airflow to the air cleaner is not obstructed.
- Keep outside doors and windows closed to prevent additional particles from entering the room.
HVAC system upgrades
If you have central air conditioning, you can install or upgrade to a high-efficiency filter (MERV 13). Run the system’s fan as often as possible to get the most out of the filter.
Box fan filter systems
You can make a do-it-yourself (DIY) air cleaner by attaching a high-efficiency filter (MERV 13) to a box fan with a bungee cord or tape. There is some limited evidence that this type of air cleaner can be helpful.
Triangle-shaped versions may be more stable in a rambunctious household. However, they may not be as effective, since PM2.5 can travel through the cardboard used to bridge the gap between filters.
See the video How to make your own clean air fan from the Washington Department of Ecology. Be sure to place the filter so that the arrows point toward the box fan on the air intake side.
Use the device with caution. It's possible that the box fan motor could overheat when a filter is attached. Do not operate the device unattended or when sleeping.
- Minimize exercise: Reducing your activity level is the best way to reduce the amount of pollution you breathe into your lungs.
- Drink plenty of water: Water helps minimize a scratchy throat and coughing.
- Stay cool: Run fans, window air conditioners or central air conditioning.
- Keep calm: Learn more about how to stress less to improve your resilience in a disaster.
AirNow. Environmental Protection Agency (EPA) and partners.
Create a Clean Room to Protect Indoor Air Quality During a Wildfire. Environmental Protection Agency (EPA).
Frequently Asked Questions About Wildfire Smoke and Public Health. Oregon Health Authority.
Extremely High Levels of PM2.5: Steps to Reduce Your Exposure. AirNow, Environmental Protection Agency (EPA).
Health Tips for Wildfire Smoke. Deschutes County Health Services.
How to Make Your Own Clean Air Fan. Washington Department of Ecology.
National Ambient Air Quality Standards. Environmental Protection Agency (EPA).
Oregon Air Quality Map. Oregon Department of Environmental Quality.
Particulate Matter (PM) Pollution. Environmental Protection Agency (EPA).
Wildfire Smoke and COVID-19: FAQs. United States Department of Agriculture, Northwest Wildfire Coordinating Group.
Wildfire Smoke and Your Health. Oregon Health Authority.
Wildfire Smoke Guide in Sections—Chapters 1–3. AirNow.gov sponsored by the Environmental Protection Agency and partners.
Wildfires and Indoor Air Quality. Environmental Protection Agency (EPA).
Diana Rohlman, PhD. Assistant Professor (Sr. Res), College of Public Health and Human Sciences, Oregon State University.
Theresa C. Mayhew, MA, Family & Consumer Sciences Resource Educator, Cornell Cooperative Extension