ASHRAE Standard 241 – Control of Infectious Aerosols

Published by Sumayyah Theron

Over the past century, indoor air quality (IAQ) standards have largely overlooked explicit requirements for managing airborne infection risks, except for those tailored to healthcare facilities and laboratories. In 1895, the American Society of Heating and Ventilating Engineers (ASHVE), later becoming ASHRAE, introduced ventilation recommendations to curb disease transmission. These recommendations were integrated into proposed laws in 1914, and by 1922, they had been adopted by numerous U.S. states. However, IAQ standards from the 1930s onwards shifted focus primarily to perceived air quality, control of chemical and particulate contaminants, and minimized ventilation rates. Only in recent years has there been an increased recognition of the pivotal role that indoor environments play in disease transmission. ASHRAE’s contributions to this field include position documents in 2009 and 2022, addressing airborne infectious diseases and aerosols specifically. Despite sporadic concerns stemming from smaller epidemics, substantial changes to standards and codes have been lacking, even though the likelihood of a major infectious event akin to the 1918 influenza pandemic has remained high.

This year ASHRAE Standard 241, titled “Control of Infectious Aerosols”, was released. It acknowledges the crucial role of maintaining good indoor air quality (IAQ) in preventing the spread of infectious diseases. Its primary objective is to establish minimum requirements that mitigate the risk of disease transmission through infectious aerosols in various indoor spaces. The standard applies to new buildings, existing buildings, and major renovations, encompassing the design, installation, commissioning, operation, and maintenance of outdoor air systems and air cleaning systems.

Key areas covered by this standard include:

1. Ventilation: Stipulating the necessity of effective ventilation to dilute and eliminate airborne contaminants, with detailed guidance on ventilation rates, outdoor air intake, and air distribution to optimize IAQ.
2. Filtration: Advocating the use of high-efficiency air filters capable of capturing minuscule particles, including infectious aerosols. The standard meticulously outlines practices for filter selection, installation, and maintenance to ensure their utmost efficiency.
3. Air Cleaning: Encouraging the incorporation of air cleaning technologies within HVAC systems and individual rooms to complement filtration efforts. These innovative technologies, such as ultraviolet germicidal irradiation (UVGI) and photocatalytic oxidation, play a pivotal role in deactivating or removing infectious particles, thereby elevating overall IAQ.
4. HVAC System Operation and Maintenance: Signifying the importance of appropriate HVAC system operation and consistent maintenance to ensure optimal IAQ. The standard provides guidelines for monitoring, cleaning, and disinfecting system components, thereby minimizing the potential risk of contamination.
5. Commissioning: Very critical as it verifies that the specifications pertaining to controlling infectious aerosols and sustaining optimal indoor air quality (IAQ) are adhered to. This process involves confirming the proper design, installation, and functionality of ventilation systems, air cleaning technologies, filtration systems, and other outlined components. Commissioning serves as a quality assurance protocol, identifying and rectifying deviations or issues during the setup and operation of HVAC systems and air cleaning technologies. It assures the correct calibration of systems, ensuring they provide the desired levels of ventilation and contaminant control, effectively countering the dispersion of infectious aerosols. The inclusion of commissioning as a vital step in these guidelines ensures that IAQ services and building operators rigorously adhere to a process that guarantees the faithful execution of recommended measures. Consequently, this contributes to the standard’s objectives in generating healthier indoor environments and diminishing the risk of disease transmission.
6. Building Occupancy: The standard recognizes two distinct occupancy modes that influence IAQ-Normal Occupancy mode and Occupancy anticipated during Infection Risk Management Mode (IRMM). These modes impact ventilation and air cleaning requirements, allowing for effective IAQ management across diverse scenarios.

In conclusion, Standard 241 is poised to profoundly affect IAQ services, as it firmly prioritizes optimal IAQ and effectively tackles the dispersion of infectious aerosols, thereby fostering an environment that prioritizes safety and well-being. At Cyclone Energy Group, we are dedicated to offering comprehensive services in Commissioning (Cx) and Indoor Air Quality (IAQ). If you’re seeking expert assistance in implementing these crucial standards and creating healthier indoor environments, we invite you to reach out to us. Let us help you ensure that your spaces are optimized for comfort, health, and safety.