Protect yourself from unhealthy air in wildfire zones

As this is written, the US west coast is under a “Siege” from hundreds of wildfires triggered by unusually hot weather. Millions of acres of wildfires have burned over the last month in California alone, with millions more acres burning in Oregon and Washington State. If Climate Scientists are correct, this sort of scenario will repeat itself more frequently over the coming years. That means we as individuals must learn how to handle protecting ourselves when (not if, but when) the outside air becomes unhealthy due to a nearby wildfire.

Currently the CalFire (California’s fire protection agency) website notes this: “Since the beginning of the year, wildfires have burned over 3.1 million acres in California. This year’s acres burned is 26 times higher than the acres burned in 2019 for the same time period.” That was written in early September 2020, so in that time period the 3.1 million acres burned so far is 26x the amount burned by California wildfires in 2019 before early September 2019.

The image at the top shows the result of the 2020 wildfire season not just in California but the rest of the West Coast. There are dozens of wildfires, including one covering over 800,000 acres that is largely uncontained. The natural terrain of the Western USA naturally involves occasional wildfires. The ecosystem of the West is generally dry, making occasional wildfires a natural occurrence. But given the overall warming of the global climate, areas like the Western USA that were already dry are becoming ever more dry every year.

This results in more frequent wildfires of greater intensity. The 2020 wildfire season has caused unhealthy air for most of the residents of California, Oregon and Washington State. In the image above the grey zone represents the smoke generated by the millions of acres of wildfires over the last month. Widespread evacuations have been ordered for folks in the path of wildfires. It’s reported that over 500,000 have been ordered to evacuate in Oregon alone — is there that many hotel rooms in Oregon?

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At a personal level it should raise the question of how to stay safe when the air outside is extremely unhealthy. It is known that air full of soot and smoke is dangerous for everyone, especially those with cardiovascular issues.

To demonstrate by way of example, let me explain what we have done in our house. This house does not have a central HVAC system, and therefore no opportunity to filter the air at the whole-house level. But we have implemented a system where one zone in the house has very healthy air, while the air outside is downright unhealthy.

Air quality index

US EPA air quality index – From Wikipedia

We first need to understand how to reliably measure the air quality. An Air Quality Index (Wikipedia) is a computed value representing how healthy or unhealthy the air is. Different governments have differing air quality index computations, but generally it is a numeric value based on measuring pollutants, and categorizes risk factors. The US EPA has a web page describing the health impacts of AQI ranges in more detail, and the general health impacts of each AQI category. Basically when the air is in the unhealthy, very unhealthy, or hazardous zones, your life is at greater levels of risk.

AQI readings during the 2020 California wildfire season – from

These are AQI measurements in a portion of California and Nevada in the middle of a time of bad air quality. The current weather does not have enough wind to dissipate the smoke, and we see readings up to 624 near the North Complex fire (Plumas and Butte Counties), and as high as 688 near the Creek Fire (Fresno area). Within the SF Bay Area the AQI readings are nearly 200 with some places reading well above. That means a large part of this area has air quality in the unhealthy, very unhealthy, or hazardous ranges.

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Two non-government resources are and Both websites have crowd-sourced air quality measurements from around the world presented on a map. The US EPA operates, which includes a map showing air quality around the USA. There may be other air quality monitoring websites, for example performs this service in the Bucharest area.

Another resource is a portable air quality monitor like this:

This portable air quality monitor shows that Bucharest air quality, measured in December 2018 at the center of a very busy intersection, borders on the unhealthy range.

This meter does not show AQI numbers, but instead shows a raw measurement of PM2.5 (particulate matter 2.5 microns), PM10, HCHO (formaldehyde) and TVOC (volatile organic compounds). It is useful for a rough estimate of air quality, and the color coding does match the US EPA AQI color coding. To explore such products click on this affiliate link.

Having learned some basics about how to measure air quality, let’s get back to the issue of protecting yourself and your family if the outside air goes bad. The rest of this post will describe how we created a green zone of clean air inside our house despite the unhealthy air outside.

My first time doing this was in November 2018, during the time the town of Paradise CA was destroyed in another wildfire. Despite that city being 150 miles from our house, the smoke plume reached us causing horrid air quality for a few days. I learned from a friend that one can attach the sort of air filter used in HVAC systems to a regular household fan, and have a DIY air filtering system.

Let’s start with an outdoors reading:

Outside air quality measurement, September 12, 2020, in Santa Clara

This is what we measure outside our house. The air had a definite smokey smell, and the meter shows it being unhealthy.

It was informative to test in different zones around the house. For example in one area we have a number of trees and bushes and the PM2.5 number dropped significantly near those bushes.

That gives us a hint that perhaps plants have a beneficial impact on air quality. Put on your TODO list a task to learn whether indoor plants will help manage indoor air quality.

Air quality inside the living room

Immediately inside the front door we measure this. It is outside the green zone we created inside the house, but it is still much better than the outside air. The difference is the fact of being inside the house, rather than outside. The windows in this house seal very well, as do the two doors that go outside. While this is a great improvement over the outside air, it is borderline unhealthy.

That means the first level of defense is your house or apartment, and its doors and windows. Make sure the windows and doors seal fairly tightly.

Air quality measurement in the kitchen

This was measured in the kitchen area of the house, still outside the green zone. We haven’t cooked anything all day, and we notice that the act of cooking will cause the PM2.5 and PM10 measurements to shoot into the 200’s. Think about that the next time you cook something like a steak dinner, that the smell of cooking is actually a form of air pollution.

What is this green zone I mention? We used some boxes to block the entry into the back hallway, limiting air flow in the area of the bedrooms and bathroom. Within that zone we set up some fans to which we’ve attached filters, so that the air within that zone is fully filtered and cleaned.

Inside the green zone we have clean air

This is our green zone. In the foreground you see the meter, and relatively good air quality readings. In the background you see one of the fans, as well as the entries blocked using boxes.

There is better air quality further inside the green zone

This is inside the bedroom I use as an office, and the air quality is that much better. In the background is a second fan that provides additional filtering beyond the fan shown earlier.

The implementation of the green zone requires multiple fans, each with air filters attached, and blocking the entrance to the green zone to preserve the bubble of clean air.

Our green zone is literally that simple. The filter attached to this fan is simply the sort of filter that’s used in an HVAC system. What’s required is to buy a filter rated for the highest grade of filtration.

For the fan in the foreground I cut a 16×25 inch filter in half and attached it using bungee cords. The fan in the background is a typical cheap “box fan”, and it has a 20×20 filter taped to the back. In the bedroom we have two more fans, also with portions of HVAC-style air filters attached.

I’ve posted further instructions on building such DIY air filters on my other blog.

In this area of the house we have ultra clean air despite the air quality emergency going on around us. With a few more fans we could have implemented a green zone covering the entire house. In the meantime, the weather service promises a change in weather patterns that will dissipate the smoke in a couple days. But we’re not out of the woods, since it was recently announced that the newly formed La Nina climate pattern should lengthen the wildfire season maybe to December.

If more wildfires do erupt in our area this year, we’re ready with the tools and knowledge to navigate the difficult times.

About David Herron

David Herron is a writer and software engineer living in Silicon Valley. He primarily writes about electric vehicles, clean energy systems, climate change, peak oil and related issues. When not writing he indulges in software projects and is sometimes employed as a software engineer. David has written for sites like PlugInCars and TorqueNews, and worked for companies like Sun Microsystems and Yahoo.

About David Herron

David Herron is a writer and software engineer living in Silicon Valley. He primarily writes about electric vehicles, clean energy systems, climate change, peak oil and related issues. When not writing he indulges in software projects and is sometimes employed as a software engineer. David has written for sites like PlugInCars and TorqueNews, and worked for companies like Sun Microsystems and Yahoo.

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