A question we’re hearing a lot is, “What distance from the burn area should you take extra precautions?” It’s a hard question because it isn’t possible to give a precise answer due to all of the uncertainty. However, we recognize that people need some guidance in the face of uncertainty, so we’re sharing how we think about it. You can use these three questions as a guide.
Did you see it?
If you saw – or still see – visible dust or ash, you should take the extra precautions. Here are 3 tips for your home: 3 Ways to Reduce Risk from Wildfire Smoke at Home – Healthy Buildings
Can you smell it?
If you are still smelling smoke and/or ash and/or ‘fire smell’, that is most likely the off-gassing of chemicals that have been absorbed into materials in your home or school. If you can smell it, you should take extra precautions.
Can you sense it?
Use a portable air quality sensor that measures airborne particles (PM2.5) and airborne gases (TVOC). If particles are sustained above 10 micrograms/m3 and TVOCs are sustained above 500ppb, you should consider taking extra precautions. For more information on these sensors, and how to interpret the data, you can read this article. The article is written for businesses, but the information on sensors and what they measure are relevant for homes and offices, too: Harvard Business Review: It’s Time for Companies to Monitor Workplace Air Quality “
These are general guides and imperfect, but are offered to help when people are trying to navigate uncertainty. Most importantly, people should refer to guidance from local, state, and national authorities, and err on the side of being more protective. For homes, offices, schools, or businesses with visible soot and ash, we would recommend professional testing and professional clean-up, and using extra precautions, including respiratory protection.
Resources:
https://www.nytimes.com/wirecutter/reviews/masking-after-wildfires