Up to this time, there is no evidence of COVID-19 transmitting through the ductwork of an HVAC system to infect individuals in other rooms or other areas in a building. In cases where ventilation has played a role in outbreaks, the ventilation failure affected individuals in the same room and precisely at the same time as the index patient is there.
This contrasts with other airborne diseases such as chickenpox or measles, which can travel meters or transmit to others even after the index case has left the supposed site of infection (for example, pediatric waiting room). Being close to the index case appears to have a severe role in COVID-19 transmission.
Possibly the most closely examined (and most publicized) example of possible short-range aerosol transmission happened in a restaurant in the early days of the pandemic. At first, transmission from the index patient to nine other people happened because of a small split air conditioner pushing large droplets farther than anticipated. However, additional studies using tracer gas measurements and airflow simulations unveiled that the room also had minimum fresh air input (<1 L/s per person), and also the exhaust grilles were sealed.
The only ventilation was provided by people who regularly opened the fire door. This lack of airflow, in addition to local air conditioning, might have formed a small pocket of air at one location of the room in which droplets from the index patient could have accumulated and circulated, which resulted in short-range aerosol transmission to those who also spent enough time in the pocket (more than 4 m away). No staff or patrons outside that district were infected, which might have resulted from this pocket influence or the dilution of particles as they diffused away from the source.
Thus, spaces with insufficient fresh air supply and/or unbalanced supply and return airflows may create the opportunity for COVID-19 particles to build up and transmit more efficiently past 2 m. Therefore, HVAC systems’ most likely role in the pandemic is alleviating close-range transmission between people sharing the same space rather than spreading the disease to distant locations.
Another sample in which we might wait to see advanced disease transmission is when turbulent or profoundly directional airflow either hinders particles from settling or directly conducts particles from one person’s breathing area into another’s. An example of this concept may have occurred during a bus trip, in which the index patient spread the virus to 22 other passengers dispersed throughout the bus. Remarkably, passengers sitting near the only open window did not contract the virus. The authors attributed the diffusion throughout the bus to recirculation through the air conditioning system; however, dispersion could also have been achieved by the strong drafts from the open window.
As a result of these incidents, a great deal of concern has been raised regarding employing fans and air conditioners. Guidance documents regularly recommend against blowing air across several people but rather to direct the airflow upward or at a wall to cool the location without creating drafts. In addition, because fans and air conditioners recirculate the air in the room without filtration, they should only be used in rooms with satisfactory ventilation. It should also be mentioned that extreme heat can be dangerous. In communities where the COVID-19 case rates are low, the risk of death resulted from heat intensity may be higher than that of COVID-19. In such cases, air conditioners and fans may be life-saving devices, which can and should be used with the precautions aforementioned above.
Fewer faces resulted from bigger spaces
In concept of ventilation and COVID-19, several other incidents have been largely or uncritically attributed to insufficient ventilation, such as an outbreak in a Healthline fitness class or call center. This assumes that sufficient or even improved ventilation could have inhibited or restricted the outbreak.
About the case of the Healthline class, participants were involved in high-intensity activities which generating lots of droplets for 50 minutes. On the other hand, the participants danced back and forth through the turbulent plumes of droplets produced by their classmates’ inhalation and exhalation. Moreover, in the case of the call center, outbreaks included crowding, constant vocalization (talking, warbling), and regular mixing/interaction.
Since all of these events presented an adequate opportunity for exposure to those larger and higher-risk droplets, it is unclear whether improved ventilation would have had a notable effect on minimizing transmission. This does not mean that ventilation cannot effectively diminish droplet numbers. Some researchers recently demonstrated that opening a window in a well-ventilated room lowered the half-life of 5 micrometers droplets to 30 sec compared to about 5 min in an unventilated apartment. However, the most practical means of reducing transmission when bodies congregate is to lessen the production of droplets (source control or more scattered people) and restrict the overlap of breathing zones (use of partitions and controlled crowding).
In ventilation and COVID-19, given the risks of under-ventilated spaces, duct air filters, and portable air cleaners came interest as a tool for lowering COVID-19 transmission. Although there is no clinical evidence to show that air filtration affects COVID-19 transmission, properly operating units with firmly sealed filters should reduce respiratory particles in the air, which may reduce the likelihood of transmission. However, as emphasized above, these devices should not be relied upon as a primary means of infection control, as poor placement or home maintenance of the device may render them less effective or create a false sense of security. The first and most important means of reducing transmission in any space is to diminish crowding For professional Air-conditional services contact us