Managing Wildfire Smoke Indoors


| Indoor Air Quality, Smoke Wave, Wildfire

Strategies for Mitigating Air Quality Impact

The recent excessive wildfires raging across Canada have led to a “smoke wave” across the Northeast which encompassed the Lehigh Valley. Yet, situations like the one that played out in the beginning of June are not an on-off event. According to the Canadian Government’s National Wildfire Situation Report, as of June 20, 2023, 385 fires are burning across Canada; 130 are considered uncontrolled, and at this point in 2023, over 5.8 million hectares have burned. Projected weather patterns and the resulting movement of the wildfire smoke indicate there is potential for the Lehigh Valley to be repeatedly impacted throughout the summer by "smoke waves".

Loretta Mickley, a wildfire expert and senior research fellow at the John A. Paulson School of Engineering and Applied Sciences, co-authored a research article defining a “smoke wave” as two or more consecutive days of extreme levels of fine particles called PM2.5, emitted specifically by wildfires. Fine particles are considered especially dangerous because they’re tiny enough to penetrate the lungs and even cross into the bloodstream.

Mitigating the impacts

As a result of the ongoing distribution of smoke particles caused by the enduring wildfires, mitigation measures must be enacted. The continual wildfire expansion and subsequent smoke infiltration in the ozone caused the Pennsylvania Department of Environmental Protection on Monday, June 19, 2023, to declare a Code Orange Air Quality Action Day for the Lehigh Valley. The Air Quality Index rates air quality from green for good to maroon for hazardous, is particularly helpful because it simplifies complex variables that change from pollutant to pollutant and links them to physiological impacts.

The solution for avoiding the fine particulate matter caused by wildfires seems simple, stay inside. Yet, in response to the COVID-19 pandemic, many internal HVAC systems were upgraded to higher efficiency filters while bringing in additional outside air for ventilation. 

COVID-19 protocols for Indoor Air Quality (IAQ) suggested filtration and dilution by bringing in as much outdoor air as possible. As a result of the smoke, the guidance is to minimize outdoor air. For HVAC systems, this translates to keeping windows closed, minimizing outdoor air dampers by removing economizer sequences, manually closing dampers and windows, and raising demand control CO2 setting. The particulate matter sensors installed during COVID-19 are not sensitive enough to measure smoke particles, but the CO2 sensors will be effective tools for measuring resultant changes in HVAC sequences of operations.

Filtering out smoke waves

What is smoke particulate matter and how does it differ from COVID-19 particulate matter?

  • Smoke particles range from 0.4 microns to 0.7 microns. COVID-19 particles are attached to water molecules and range from 5-10 microns. This means that smoke particles are smaller, thus more capable of impacting those with health conditions such as asthma, chronic obstructive pulmonary disease, and heart disease. 

Are there air filters that can remove smoke particles from the air?

  • Yes. MERV 13 filters are the most frequently used type of air filter for central systems. The MERV 13 air filter is designed to remove particles from the air that are larger than 0.30 microns. Meaning the MERV 13 air filter is capable of minimizing and removing smoke particulate matter. Portable filter units with HEPA filters are more effective and can be used in individual spaces. 

Are there masks that can filter smoke particles?

  • Yes. N95 masks - assuming they fit snugly - are tested by NIOSH to be 95% effective for filtering particles down to 0.3 microns.

What adjustments should be made to HVAC systems?

  • Minimize the introduction of outdoor air and filtration via HVAC systems to limit the re-circulation of potentially contaminated outdoor air. 
  • HVAC units with MERV-13 filtration should be set to run continuously to maximize filtration passes.  Many units will cycle on and off if the temperature is satisfied, but they can be set to keep air constantly moving.  

To learn more about HVAC, MERV filters, and their ability to limit particulate matter, click here

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