ASHRAE Publishes “First of its Kind” Risk Mitigation of Infectious Aerosols
Walt Vernon, PE, LEED AP, EDAC, FASHE
Principal, Chief Executive Officer
Infectious Aerosols is a public interest issue and the magnitude of risk from aerosolized pathogens has become increasingly obvious, especially during the COVID crisis. These risks are particularly elevated in enclosed buildings. Public-health officials, policymakers, building owners, designers, and members of the public all need accurate, reliable guidance for appropriate ways to mitigate the risk from these pathogens.
I was honored to be selected to chair the re-write (with contributions from Mazzetti colleagues Jim Crabb and Troy Savage) of the critical document, “ASHRAE Positions on Infectious Aerosols” which succinctly summarizes the available evidence and sets forth the official positions of the organization for implementation. ASHRAE consensus standards and design guides provide the technical foundation for international building practices and energy codes that balance the need for energy efficiency with the need to keep the indoor environment healthy and comfortable for occupants. The design, installation, and operation of buildings’ mechanical systems can improve—or impede—the buildings’ ability to mitigate risk from infectious aerosols. Consequently, ASHRAE’s positions, standards, and design guidance can help avoid health risks associated with infectious aerosols.
Historically, ASHRAE documents have focused ONLY on the use of ventilation and its impacts, ignoring other available risk mitigation measures. The new document proposes new methodologies for use in this kind of work and the new Infectious Aerosols Position Document (IAPD) considers ventilation in the context of a wide range of potential interventions.
The IAPD used a form of Evidence Based Medicine (EBM) which looks at the amount of benefit from a particular intervention (in this case ventilation as a risk mitigation measure), the amount of evidence that supports that benefit, and the potential harmful side-effects of the particular intervention. This is one of the first times this kind of analysis has underpinned such an effort from ASHRAE, and it sets a needed precedent for future efforts.
In terms of potential harmful side-effects, this version of the IAPD looks at first cost, ongoing costs, and climate impacts, as directed by the ASHRAE Board. Again, this is one of the first times that harmful side-effects have been explicitly cited and considered in developing needed risk mitigation policy.
Last, the new IAPD considers changes of state. The risk from infectious aerosols is not constant. So, dictating a constant solution is unlikely to result in optimal results. The new IAPD considers different risk states, including velocity of change between risk states, an incredibly important factor in determining the optimal public policy response.