A warmer climate and arid conditions have contributed to more frequent and intense wildfires across the U.S.
More than 32,000 wildfire incidents have been recorded through Aug. 27, with about 2 million acres burned in large fires, according to the National Interagency Fire Center.
In addition to the obvious threats wildfires pose to land, structures and people, they emit pollutants that can enter buildings. Such pollutants include formaldehyde and ozone, volatile organic compounds, toxins, airborne pathogens and particulate matter. In the U.S., wildfires are the biggest source of PM2.5 — particulate matter that’s 2.5 micrometers in diameter or smaller — accounting for 30% of total emissions across the continental U.S., Sissi Liu, CEO and co-founder of Metalmark Innovations, an indoor air quality startup, noted in a presentation at the 2024 ASHRAE annual conference.
Hazardous gas emissions from incinerating products and building materials can also contain harmful components like benzene, phenols, sulfur dioxide and hydrogen sulfide, David Schaaf, director of molecular filtration at Mann+Hummel, said in his presentation during the seminar.
“These contaminants are brought inside through infiltration, pressure differential, doors and windows, clothing, human and pet foot traffic and HVAC system intakes,” Schaaf said. “In some cases, the contaminant concentrations inside of buildings remain elevated after a wildfire event due to ineffective or inadequate filtration.”
Existing guidelines for wildfire smoke exposure, like ASHRAE 52.2 and many other standards, are based on previously established guidelines for non-smoke PM2.5 and do not account for the submicron size range of most particulate matter emitted from wildfires, according to Liu.
Despite the limitations of current guidance, Liu and other experts at the conference outlined the following ways owners and operators can prepare for wildfire events and protect against their harmful effects on indoor air quality.
1. Have a plan
Protection from the indoor air quality impacts of wildfires starts with planning and preparation, according to Michael Gallagher, president of mechanical systems contractor Western Allied Corp. and voting member of the subcommittee that created ASHRAE’s proposed Guideline 44, Protecting Building Occupants From Smoke.
Despite the increasing frequency of wildfires and their health impacts, many building owners, operators and facilities staff remain unprepared to address these risks effectively, Gallagher said during a presentation at the conference.
With most communities receiving only 24 to 48 hours’ notice of wildfires, it will be too late to mitigate the fires’ impacts on IAQ if there is no plan in place, he noted. “As you all know, nothing good happens at the last minute,” Gallagher said.
ASHRAE Guideline 44, expected to be published before the end of the year, can act as a reference point for planning, according to Gallagher. “You’re going to have to decide what needs to be done and who’s going to do it. ... And then, very importantly, you need site-specific research,” he said.
Gallagher emphasized that it may be impossible to get supplies of the core equipment wildfires require, such as personal protective equipment and air filters, during a fire event. “The first day the smoke goes, all the shelves will empty. This is the stuff that [needs] to be decided upon and secured well in advance,” he said.
Even if a building’s operations are disrupted or the facility shuts down, essential staff such as janitors, building engineers and facilities personnel will still need personal protective equipment, Gallagher said.
Gallagher provided questions to start the planning process:
- Will the building be occupied during a smoke event?
- Are you planning on the building being occupied for a day, or for the duration of the event?
- Will there be schedule changes in the building?
- Will there be a designated area of refuge within the building, or will the entire building be occupied?
- Does an accurate air filter list exist?
- What filters are you currently using, and what is the cost for each set?
- How will you adjust for the minimum outside air positions?
- How can you reduce or manage outside air intake and exhaust?
2. Upgrade your air filters
To better protect building occupants against smoke and the particles it can contain, Schaaf recommends that building operators use pre-filters or final filters with a minimum MERV-13 rating. Over 80% of PM2.5 particles can pass through MERV-8 filters and permeate occupied spaces, he said, whereas MERV-13 filters can block up to 80% of such particles. However, blocking 80% of these particles may not be sufficient because wildfires commonly produce PM2.5 concentrations as high as 300 to 500 micrograms per cubic meter, according to Schaaf’s presentation.
If an HVAC system does not provide sufficient fan pressure for that degree of filtration, operators should change the filters before they are fully loaded, he added.
Schaaf recommends replacing 2-inch to 4-inch pleat combination pre-filters with 12-inch combination final filters when retrofitting molecular filters into an HVAC system. Portable air cleaners with a HEPA filter may be helpful in removing smoke particles as well, according to a 2021 paper from the U.S. Environmental Protection Agency.
Air filtration needs have practical considerations as well, Gallagher said. If a building is ventilated at normal rates, without making any equipment changes, “you can’t stock that many filters,” he noted. “Based on prior experience, if you need to plan for at least a week or two of a smoke event, that’s probably a new set of filters every other day. If it’s intense, that’s a lot of storage space, but it’s also a lot of trash.”
3. Reduce outside air intake
“If you don’t take anything else away from this, other than the necessity of planning, what you need to do is figure out the least amount of outside air you can bring in and maintain positive pressure,” Gallagher said. “And you have to narrow it down to the least number of locations in which you are bringing it in. You have to have positive pressure, otherwise infiltration will kill you with wildfire smoke.”
While preparing for wildfire events takes time for research and planning, it also requires commitment on the part of the facilities department and resources from the facility owner. “Somebody’s going to have to take them through the process. … You’re going to have to get resources from that organization,” Gallagher said.
The silver lining of increased wildfire risk, he said, is that “a lot of North America has seen [wildfires] happen,” which should make it easier to get building owner support for mitigation planning and preparation. “There’s a solution. There are things to be done.”