Smoky air can range from a minor annoyance to a serious health problem. When you have to seek refuge indoors, improve the quality of your home's air with these ideas from Mark Fretz, assistant professor at the University of Oregon Department of Architecture.
Along with many diverse, innovative projects that connect architecture and public health, Fretz studies the air inside the buildings where we live and work. A former dentist and lieutenant officer with the U.S. Public Health Service Commissioned Corps, he combines various research disciplines to explore the great indoors.
Fretz is codirector of the UO Institute for Health in the Built Environment and Energy Studies in Buildings Laboratory, both based in the College of Design. In 2019, Fretz and a team of researchers released guidelines for reducing indoor transmission of COVID-19. Fretz and his UO colleagues have also published a guide for the Oregon Health Authority that helps residential healthcare facilities improve air quality to reduce disease transmission.
As wildfires burn across Oregon, we caught up with Fretz to talk about indoor air pollution. He outlined some essential steps you can take to stay healthy when smoke blankets the region.
10 tips for dealing with smoke
- Keep windows and doors closed
- Weatherize your home
- Use a strip of tissue to investigate areas of air leakage
- Use mechanical filtration, such as a portable High Efficiency Particulate Air, or HEPA air filter, or build a Corsi-Rosenthal Box
- Keep your central air system running in fan mode, even if it's not heating or cooling
- Make sure your vacuum cleaner has a HEPA filter
- Avoid other activities that affect indoor air quality, such as burning candles, frying food or smoking
- Stay inside as much as possible
- Wear a well-fitting N-95 respirator outside
- Keep your interior relative humidity within 40-60%
Q: What's the most important trick to keep smoke out of my home?
Close your doors and windows. You've probably heard that before, but it's sound advice. And you can take other steps related to basic weatherization. We call it "tightening the envelope" to create an enclosure around your home that prevents air infiltration.
Q: So how do I tighten my home's envelope?
Seal up all gaps and cracks where air can flow. That includes adding weather stripping or caulk around windows and doorways. Older homes may require installing storm windows or temporary shrink-to-fit plastic wrap over windows. Make sure your exhaust vents have working dampers that allow air out, but not back in.
Q: Are there additional benefits from a tighter envelope?
Yes. It will help keep your home warm in winter and cool in summer, reducing your energy bills.
Q: What about air filters?
Mechanical filtration that removes fine particles is the gold standard for clean air. If you have central air, add a High Efficiency Particulate Air, or HEPA, filter if you don't have one already. Keep your central air running in fan mode, even if you're not heating or cooling your home. It will still circulate and filter the indoor air.
Q: How do those filter ratings work?
If the filter says HEPA, you're set. It has been tested to remove 99.97% of particles for the worst-case particle size. You may also see a Minimum Efficiency Reporting Value, or MERV, rating. MERV is tested for a range of particle sizes and rates efficiency on a scale of 1 to 16, so that you can compare filter performance. The higher the MERV rating, the better; however, ideally use MERV 13 or higher.
Q: What if I don't have central air?
Use a portable HEPA air purifier, ideally one with a prefilter. Operate it in an open space that's not obstructed by furniture or behind a door. The key is to keep as much air as possible mixing and circulating. The more air you move through the filter - and the higher its efficiency rating - the better. You should choose an air purifier that is rated to meet or exceed your room size and run it at the highest speed for best results. Also, run your air purifier where you spend the most time, such as your bedroom.
Q: Is there an alternative to portable HEPA filters?
Yes, if you can't access a HEPA filter, build a Corsi-Rosenthal Box with four square air filters for a central air system, plus a box fan and duct tape. You can find the materials at most hardware stores.
Q: Should I keep my AC running when it's smoky?
Yes. Central air systems have filters that can help remove indoor particulates while running. Window and portable air conditioners and ductless heat pumps all circulate indoor air but generally offer no filtration. They are still important on those hot days with closed windows, though should be paired with a portable filter. Observe how your AC operates, and you'll notice it does not pull in air from outside but recirculates indoor air. Anyone can investigate their home's air flow and pressurization to understand where particulates might be moving.
Q: What's pressurization?
Buildings often have pressures that build up between rooms or between the outside and inside. When wind blows against the house, one side has positive pressure while the opposite side has negative pressure, like a vacuum. Exhaust fans for bathrooms or kitchens can also create negative pressures inside because they're pushing air outside that gets replaced by air drawn back in. These pressures move air through small cracks in walls or other openings bringing fine particulates from outdoor smoke. Therefore, avoid using kitchen or bathroom vents continuously when outdoor air quality is poor.
Q: How can I figure out my pressurization?
Tear a strip off a tissue. Hold it up to windows, doors, corners, outlets or anywhere you suspect air is moving. The strip's motion will indicate air flow direction, so you know whether air is coming in or going out.
Q: Does humidity matter?
Absolutely. Keep relative humidity between 40-60% so particulates cling to water droplets and fall. If the air is too dry, particulates stay suspended more readily and our respiratory system has less protection. But relative humidity above 60% encourages microbial growth
Q: Any other tips?
For good indoor air quality, avoid burning candles, frying food, smoking and using a vacuum cleaner that doesn't have a HEPA filter. All of those add unhealthy particulates to your indoor air in addition to wildfire smoke.
Q: How are UO researchers working on indoor smoke issues?
One solution we're studying is passive cooling. The simplest form of passive cooling is opening your windows at night, but that's not a good idea when it's smoky. Having to keep windows closed during hot weather can also put people under increased heat stress, which is another public health issue.
Instead, we're looking at how to make passive cooling possible even when the outdoor air quality is bad, such as design strategies that keep the air you breathe separate from air that's circulating outside and cooling the home. As an added bonus, passive cooling still works when the power goes out.
