Q. Can HVAC systems play a role in transmission of the virus within a workplace? And is there direction on cleaning protocols or maintenance standards for workplace HVAC systems – either with respect to enhancing current maintenance practices for workplaces where employees continue to deliver critical services; or in circumstances where enhanced cleaning is conducted?

A. We performed a rapid search of the literature on HVAC systems and COVID-19 transmission, as well as cleaning and maintenance standards. Overall, we found some evidence of viral detection in air, but no reports on the viability of airborne virus or detection within HVAC systems in real world settings. Knowledge on COVID-19 continues to evolve, however the current evidence does not suggest a risk of transmission from airborne virus in HVAC systems. Some details on this:

Current evidence indicates that the virus causing COVID-19 is largely transmitted during close contact and by respiratory droplets that can be propelled for up to 2 m. Further details on routes of transmission can be found in this PHO summary.

The virus would have to become airborne and transported over longer distances, and maintain viability if it is to facilitate transmission through an HVAC system.

A recent study found that virus in experimentally generated and maintained fine aerosol droplets (versus aerosols produced by a cough, sneeze or other physiological process) remained viable for at least 3 hours after they were generated, however this does not mean that airborne transmission does occur (van Doremalen et al).

A non-peer-reviewed paper reported widespread presence of COVID-19 viral RNA in the air of negative pressure isolation rooms in samplers more than 6 feet from where COVID-19 patients were being treated; however, the presence of RNA does not necessarily indicate viable virus. No samples were collected from within the HVAC system, however viral RNA was found on the air handling grates leaving the room (Santarpia et al)

Others have found undetectable or low concentrations of viral RNA in air (Liu et al, Ong et al).

A report of a COVID-19 outbreak in a restaurant concluded that transmission could not be explained by droplet transmission alone, but that the strong airflow from the air conditioner may have moved droplets further than might be expected (Lu et al).

Yu et al. described an outbreak of SARS (not COVID-19) in a housing complex in Hong Kong where the hypothesis for spread was aerosolization of wastewater containing the virus.

With respect to cleaning protocols or maintenance standards for workplace HVAC systems:

• There is a joint standard from the American National Standards Institute (ANSI), the American Society of Heating, Refrigerating, and Air-conditioning Engineers (ASHRAE) and Air Conditioning Contractors of America (ACCA) for HVAC inspection and maintenance. This standard should be considered by facility operators in order to optimize HVAC system operation on a routine basis.
   
• ANSI/ASHRAE/ACCA standard 180-2018 (Standard Practice for Inspection and Maintenance of Commercial Building HVAC Systems) details procedures and establishes minimum HVAC inspection and maintenance requirements that preserve a system’s ability to achieve acceptable thermal comfort, energy efficiency, and indoor air quality in commercial buildings (ANSI/ASHRAE/ACCA,2018).
   
• ASHRAE also released guidance for building operations during the COVID-19 pandemic (Schoen). In addition to measures such as increased disinfection and enabling hand hygiene in buildings, suggestions for HVAC operations are provided:
  • Increase outdoor air ventilation (use caution in highly polluted areas); with a lower population in the building, this increases effective dilution ventilation per person
  • Improve central air filtration to MERV-13 filters or the highest compatible with the filter rack and seal edges of the filter to limit bypass
  • Keep systems running longer hours, if possible 24/7, to enhance the two actions above
  • Consider portable room air cleaners with HEPA filters
  • Consider UVGI (ultraviolet germicidal irradiation), protecting occupants from radiation, particularly in high-risk spaces such as waiting rooms, prisons, and shelters
  • Usual precautions when dealing with potential infectious diseases (e.g., in a hospital HVAC system), should be followed by HVAC technicians if COVID-19 is a concern in the building

References:

van Doremalen N, Bushmaker T, Morris DH, Holbrook MG, Gamble A, Williamson BN, Tamin A, Harcourt JL, Thornburg NJ, Gerber SI, Lloyd-Smith JO. Aerosol and surface stability of SARS-CoV-2 as compared with SARS-CoV-1. New England Journal of Medicine. 2020 Mar 17.

Santarpia JL, Rivera DN, Herrera V, Morwitzer MJ, Creager H, Santarpia GW, Crown KK, Brett-Major D, Schnaubelt E, Broadhurst MJ, Lawler JV. Transmission Potential of SARS-CoV-2 in Viral Shedding Observed at the University of Nebraska Medical Center. medRxiv. 2020 Jan 1. (not peer-reviewed)

Liu Y, Ning Z, Chen Y, Guo M, Liu Y, Gali NK, et al. Aerodynamic Characteristics and RNA Concentration of SARS-CoV-2 Aerosol in Wuhan Hospitals during COVID-19 Outbreak. bioRxiv. March 10, 2020. (accessed April 6, 2020, not peer-reviewed) 

Ong SW, Tan YK, Chia PY, Lee TH, Ng OT, Wong MS, et al. Air, surface environmental, and personal protective equipment contamination by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) from a symptomatic patient. JAMA. 2020 Mar 4

Lu J, Gu J, Li K, Xu C, Su W, et al. COVID-19 Outbreak Associated with Air Conditioning in Restaurant, Guangzhou, China, 2020. Emerging Infectious Diseases. 2020 July. (accessed April 6, 2020)  

Yu IT, Li Y, Wong TW, Tam W, Chan AT, Lee JH, Leung DY, Ho T. Evidence of airborne transmission of the severe acute respiratory syndrome virus. New England Journal of Medicine. 2004 Apr 22;350(17):1731-9.

ANSI; ASHRAE; ACCA. ANSI/ASHRAE/ACCA Standard 180-2018 -- Standard Practice for Inspection and Maintenance of Commercial Building HVAC Systems, 2018. Accessed April 6, 2020. 

Shoen, L.J. Guidance for Building Operations During the COVID-19 Pandemic. March 24, 2020. ASHRAE Journal Newsletter. Accessed April 6, 2020.   “