The recent release of the above-mentioned standard by ASHRAE (www.ashrae.org) represents a significant development on the role of infectious agents in indoor air quality (IAQ) in the built environment. Notably, and with the exception of its position paper (2022) on infectious agents in indoor air, it is the first standard of its kind from ASHRAE, a large and highly respected standards-setting organization. ASHRAE, which has been around for well over a century now, recently recognized that its rosters lacked explicit requirements on risk management from airborne infectious agents.
The co-incidental pandemic of COVID-19, with its unprecedented and on-going impact on human health and economics and closure of public buildings, catalyzed the urgency for a suitable standard to mitigate the role of indoor air as a vehicle for infectious agents. Therefore, in December 2022, ASHRAE’s Board of Directors authorized the development of a new standard with the primary focus on the potential of indoor air to spread infectious agents and approaches to risk reduction. The draft standard was subjected to public comments and was approved for publication in June 2023.
The standard applies to a wide variety of buildings and space types with the objective to establish minimum requirements for control of infectious aerosols to reduce risk of disease transmission in the occupiable space in new buildings, existing buildings, and renovations to existing buildings. Notably, it addresses only indoor long-range transmission due to inhalation of infectious ‘aerosols emitted by an infector who is not in close proximity to a susceptible occupant’.
ASHRAE standard’s Appendix A (normative) further specifies the following requirements for the testing:
The aerobiology chamber design
Biosafety Requirements and Microbiological Procedures
- The testing to be conducted at a third-party independent laboratory and not by the device manufacturer’s facility.
- The aerobiology test chamber shall have a volume of at least 800 ft3 (22.7 m3). Its surfaces shall be smooth, nonporous, produce minimal emissions, and react minimally with the test system; surfaces shall be electrically grounded.
- The chamber shall be airtight and have fans to provide sufficient mixing of the air inside it; it shall also have means of flushing the chamber or cleaning it between tests.
- It shall be capable of maintaining the air temperature throughout the duration of testing at 23°C ± 3°C and the relative humidity at 50% ±10%.
- Air-handling systems of the chamber ventilation shall be powered off during testing to minimize recirculation.
Biosafety Requirements and Microbiological Procedures
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- All bioaerosol testing and microbial procedures shall comply with the current version of the CDC/NIH Biosafety in Microbiological and Biomedical Laboratories.
- All effective testing shall be performed using the non-enveloped coliphage MS2 (host Escherichia coli). Informative Note: MS2 has been chosen because of its established properties as a relatively safe and conservative viral surrogate. Air cleaner device makers are encouraged to test with specific infectious agents and/or their appropriate surrogates to determine more specific performance claims against known pathogens that are outside the scope of this standard.
- The test microbe shall be aerosolized by nebulizing its suspension to produce discrete aerosols.
- The samples of bioaerosols shall be collected between 123 and 127 cm above the floor and >0.6 m from walls or equipment using impingers, impactors, or other acceptable sampling methods as determined by the third-party testing laboratory.
- The test microorganism samples shall be collected, handled, and analyzed in the same manner for all test iterations. Each collected sample shall be plated in triplicate.