ASHRAE Releases New Planning Framework for Protecting Commercial Building Occupants from Wildfire Smoke

As we saw earlier this summer, smoke from Western U.S. and Canadian wildfires impacted not just nearby states, but traveled across the country as far south and east as Boston, Washington DC and New York, prompting air quality alerts with some cities logging their worst air quality in 15 years. As the drought rages on in the West and peak wildfire season is still a month away, it is timely to review recent guidance published by ASHRAE: Planning Framework for Protecting Commercial Building Occupants from Smoke During Wildfire Events.

The Framework was developed in collaboration with the EPA and NIST to protect people in schools, commercial buildings and other public buildings from wildfire smoke exposure. The document is the first of its kind to provide information to help building owners and managers prepare for wildfire smoke in their communities and better protect their occupants. Final guidance is being developed by the committee and is expected to be completed in 2022. This ASHRAE Framework is well aligned with our recommendation to clean as much indoor air as possible, replacing only the amount needed to deliver good IAQ and maintain building pressure. Here is an overview of the ASHRAE planning framework.

Before a Wildfire:

With a primary focus on minimizing exposure to PM_2.5, the document recommends that building managers develop a “Smoke Readiness Plan” to respond to state and local smoke advisories. To develop the plan, prior to wildfire season building managers should determine an outdoor air intake level that controls odor, temperature, and CO₂ levels while maintaining a positive building pressure consistent with the building and HVAC system design.

During a Wildfire:

During a wildfire event, reduced ventilation may be acceptable for short periods to protect vulnerable populations, but care must be taken to not create a negative building pressure that draws smoke into the building. Similarly, economizer damper operation should be limited during wildfires.

In most commercial buildings, schools, multi-unit residential, and similar buildings, particularly those that use air handling units (AHUs), ASHRAE recommends MERV13 or higher efficiency filters. The document notes that if a building’s HVAC system is not able to reduce PM_2.5 concentrations sufficiently throughout the building, a cleaner air space can be created using one or more in-room air cleaners with a HEPA filter (or other high efficiency filter) in a closed room. It is important that air cleaners are correctly sized for the space, and multiple devices may be needed for larger rooms.

Other recommendations include adding a port or pressure gauge to measure filter drop in at least one AHU, weatherizing the building envelope, doors, and windows to reduce infiltration by sealing and caulking cracks, and installing one or more PM_2.5 monitors. Once the Smoke Readiness Plan is implemented, building managers should use the data from the indoor PM_2.5 monitor to determine whether the actions taken have reduced PM_2.5 levels. Building managers are also cautioned to beware of other sources of PM_2.5: cooking, vacuum cleaning, printers, copy machines, and smoking.

COVID & Wildfires:

HVAC filtration and air cleaning recommendations for smoke and SARS-CoV-2 are similar due to the similarity of their respirable particle sizes. The difference is the outdoor air ventilation rate: a low rate is desirable for smoke control and a higher rate is desirable for removal of SARS-CoV-2 virus particles unless exposure reduction goals can be achieved with high efficiency filters*. Additionally, improved HVAC filtration must clean the recirculation air to mitigate risk from SARS-CoV-2.

Building managers’ current challenge is monitoring system components and indoor conditions and changing system settings as outdoor air quality changes to balance potential tradeoffs between smoke and SARS-CoV-2 exposure. In-room air cleaners with HEPA filters (or other high efficiency filters) may be helpful in removing virus particles as well as smoke particles without increasing the amount of outside air.

This new guidance comes at a time when many buildings have opted to increase ventilation rates to address indoor contaminants, necessitating costly heating and cooling of outside air. While it is tempting to view outside air as “fresh”, the widespread air quality alerts from wildfire smoke, and the recent American Lung Association 2021 State of the Air Reports’ findings that 40% of our population – over 135 million people – live in polluted air tell a different and alarming story.

As a changing climate continues to amplify drought conditions that rapidly spark wildfires in the western United States, the damaging smoke from these long-burning fires is not contained to one portion of the country. Huge swaths of the population are impacted, and we are grateful to ASHRAE for their important and timely guidance.

It is clear that we must plan ahead for a new normal, and to be prepared with durable solutions that address indoor air quality and don’t further contribute to the rise of carbon emissions that are spurring these extreme weather conditions. We commend ASHRAE for helping all of us prepare for this new reality.

^{*See the ASHRAE Epidemic Task Force Core Recommendations for Reducing Airborne Infectious Aerosol Exposure, section 2}

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