By Michael Tobias
There are still many unanswered questions about COVID-19 particularly on how it emerged, how it can be prevented, and how it can be cured. But studies carried out in recent months show there is evidence that transmission is airborne via saliva droplets and aerosol particles.
So where do engineers fit in?
The Environmental Health Committee (EHC) of the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) has considered the implications of airborne transmission of the COVID-19 pandemic very carefully, particularly in terms of engineering interventions that can be implemented to minimize the spread of the disease and how effective these are likely to be.
ASHRAE’s technical council has also reaffirmed the Society’s position on airborne infectious diseases in general.
ASHRAE & the Role of Engineers in Reducing the Risks of COVID-19
Having created an Epidemic Task Force to deal with issues relating to COVID-19, on April 17, 2020, ASHRAE’s EHC issued an Emerging Issue Brief about the airborne transmission of the pandemic SARS-CoV-2.
This brief outlined various issues, including the fact that both the World Health Organisation (WHO) and the US Centers for Disease Control and Prevention (CDC) had initially assumed that transmission would be similar to that identified when the genetically similar severe acute respiratory syndrome (SARS) emerged in 2003, with droplet transmission at close range. Even though SARS-CoV-2 has turned out to be a much more widespread and deadly disease, there is enough evidence to show that transmission through the air is probable and that exposure to any airborne virus particles should be controlled.
Because filtration and ventilation provided by heating, ventilating, and air-conditioning (HVAC) systems can reduce the airborne particles that spread certain diseases including SARS, ASHRAE has concluded that they can also reduce the airborne concentration of SARS-CoV-2 and in this way minimize the risk of airborne transmission.
In the brief, ASHRAE also warned that spaces that are “unconditioned” can be life-threatening because they can cause thermal stress to occupants. This condition can also lower a person’s resistance to infection.
Additionally, the Society also advised that HVAC systems should not be disabled in an attempt to reduce the transmission of the virus. Instead, HVAC systems should be reconfigured to help prevent COVID-19 by upgrading air filters, adding UV disinfection, and by finding other ways to make buildings less vulnerable to the coronavirus.
ASHRAE’s guidance on how to prevent the airborne transmission of coronavirus includes:
- Reducing recirculation of indoor air.
- Increasing the use of outdoor air for ventilation.
- Complementing air filtration with ultraviolet germicidal irradiation (UVGI).
- Keeping relative humidity at a range that will minimize the transmission of bacteria and viruses, between about 40% and 60%.
- Ensuring HVAC systems work properly and are inspected regularly, particularly before buildings that have been shut down during the pandemic are reopened.
This can be done by having an HVAC engineering firm identify vulnerabilities in buildings and detecting related health hazards that can be eliminated by reconfiguring HVAC systems.
Position of ASHRAE on Airborne Infectious Diseases
There are many diseases including the common cold, influenza, and tuberculosis (TB) that are known to be spread through the air. It is also an accepted fact that the spread of disease can be controlled or even accelerated by HVAC systems. Specific techniques employed via HVAC systems that are used to control the transmission of airborne infectious diseases include:
- Regimes relating to airflow
- Ventilation rates that are utilized
- Filtration
- Ultraviolet germicidal irradiation
ASHRAE has developed standards and guidelines that should be used for the manufacture, installation, operation, and maintenance of HVAC systems and all their elements. ASHRAE also has an Indoor Air Quality Guide which was prepared in 2009 in an endeavor to ensure airborne infectious diseases, including a future pandemic like the one we are currently experiencing, could be controlled.
Additionally, ASHRAE recognizes that engineers play a key role when it comes to the reduction of disease transmission in buildings.
Some of the recommendations ASHRAE makes include ensuring that:
- All facility designs follow the relevant ASHRAE standards including ventilation and thermal conditions.
- Systems designed to control airborne infectious diseases are commissioned, operated, and maintained in the correct manner.
- HVAC systems are enhanced and improved with supplemental filtration, UVGI, and possibly additional ventilation in the breathing zone, especially in new buildings where the additional costs will be moderate.
- There are infection control strategies that incorporate multiple interventions that are not only related to ventilation.
- Multidisciplinary teams including engineers, scientists, epidemiologists, infection prevention specialists, and building operators collaborate when it comes to identifying and implementing interventions that will mitigate the risks of airborne infectious diseases.
ASHRAE also believes that engineers and building operators have an important role to play in planning for emergencies that may result from the transmission of infectious diseases.
There are also issues relating to ongoing research including the need for those focusing on infectious disease to get input on various elements including methodology from discipline experts such as those mentioned in the last point above. This would provide a better picture of how disease transmission and building systems interplay.
The Society strongly believes that controlled intervention studies should be conducted so that the performance and cost-effectiveness of airborne infection control can be quantified. There should also be studies in high-risk environments including homeless shelters, nursing homes, health-care facilities, schools, and jails.
On a more technical level, there should also be research that quantifies the rate of airborne removal of microorganisms by filtration as well as inactivation by UVGI strategies so that we know more reliably how effective these interventions are.
Ultimately, we know that there is enormous potential for the airborne transmission of diseases of all kinds from common colds to COVID-19, and we know that airflow and ventilation are an effective means of controlling the transmission of some diseases. These engineering controls will certainly mitigate the risks of COVID-19.
Two results both of which relate to the ASHRAE statement that I quote, but not directly. It would be difficult to change, but if required I will.
