WBI COVID-19 Response Series: Alternative Medical Facilities & Hospital Surge Considerations

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SARS-CoV-2: Patient surge consideration and control of hospital and healthcare facility airborne infectious disease transmission through HVAC systems

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Author: Matthew B. Sunday, MSME, Wright Brothers Institute - March 31st, 2020

Without defined best practices to manage hospital HVAC during the COVID-19 pandemic, implemented air quality strategies may result in heightened SARS-CoV- 2 exposure to occupants and residence in the surrounding community.

Hospital and healthcare facilities are at a much higher risk of accelerating airborne infectious disease spread when HVAC systems utilize recirculated air. Typical system operations and minimum standards, referenced by the Centers for Disease Control and Prevention (CDC), highlight airborne contaminate removal rates, ventilation requirements, and filtration efficiencies. The CDC indicates that airborne contaminate removal times will be longer than those stated in Table 1 when in the presence of an aerosol generating source. 

HVAC systems for health-care facilities, based on the AIA Guidelines for Design and Construction of Hospitals and Health-Care Facilities (2001), have minimum air changes per hour (ACH) by area designation, reference the abbreviated summary in Table 2. Recognize that the ACH necessary to maintain a hospital without SARS-CoV-2 concerns is already an engineering and maintenance challenge. When hospitals identify a patient with an airborne infectious disease, a negative-pressure isolation room is utilized to prevent cross-contamination. These rooms are limited in number and as the COVID-19 patient admissions increase, strategies must be developed to accommodate the isolation capacity needs of these facilities. Leveraging ventilation rates, airflow regimes, differential pressure control, ionization, filtration, and ultraviolet germicidal irradiation (UVGI) can reduce virus spread. However, no single solution can be universally employed due to the variability that exists between hospital designs, regional specific environmental factors, facility limitations, and scarcity of resources for modified solutions. These are not new technologies, but their effectiveness, specifically on SARS-CoV-2, requires characterization to assist engineers in determining best practices.

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Patient Surge Considerations

Transitioning hospital HVAC systems to 100% outside air, no recirculation, is limited to only units designed for this accommodation. Increasing the ACH to create additional negative pressure rooms, floors, or facilities is a viable alternative, but only within the performance limits of the existing systems’ design. Note that in both scenarios, the heating and cooling capacities of the units will fall short of temperature and humidity requirements because they are operating outside of their original design parameters. Increased exhaust rates will exceed filtration, ionization, and UVGI design parameters and the ability to scale up these components will most likely be limited by supply chain constraints. Effective mitigation of aerosolized virus spread from these facilities must be determined to ensure that the expelled air is not a hazard to the surrounding community. As referenced from The New England Journal of Medicine (17Mar2020), “results indicate that aerosol and fomite transmission of SARS-CoV-2 is plausible, since the virus can remain viable and infectious in aerosols for hours and on surfaces up to days.”

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Alternative Medical Facilities

As the number of COVID-19 patient admissions increases, the need to distance and safeguard uninfected patients from the virus is critical. Alternative facilities will need to be identified and converted for this purpose, i.e. hotels, arenas, assembly-type spaces, etc. The mechanical systems’ capabilities, site location, and facility layout are but a few considerations that are used to determine viability. Developing a standardized strategic plan and decision matrix will help communities expedite the facility downselection process and understand tradeoffs associated with each location. A collaborative effort between the civilian medical community, local government officials, engineers, and facilities groups coupled with Expeditionary Medical Support System (EMEDS) subject matter experts can quickly define this trade-space.

Resources

https://www.cdc.gov/infectioncontrol/guidelines/environmental/appendix/air.html

https://fgiguidelines.org/wp-content/uploads/2015/08/2001guidelines.pdf

https://www.nejm.org/doi/10.1056/NEJMc2004973

https://www.ashrae.org/file%20library/about/position%20documents/airborne-infectiousdiseases.pdf

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