As new information is revealed about COVID-19, we deemed It necessary to continue to provide HVAC strategies for keeping your environment safe from disease spread. Although COVID-19 has been shown to be predominantly transmitted via human contact and indirect contact from infected surfaces, it can still move through the air – especially during operations or treatments that involve the use of aerosols. Because of this, it is to your advantage to have continuous HVAC strategies in place to ensure your building is at a healthy baseline. Then, using PPE and other large droplet precautions, you can take a wholistic approach to containing infectious disease within your building.
Just because COVID-19 has not been proven to be “airborne”, does not mean that it cannot spread through the air.
In a study published in the Journal of Aerosol Science, Pyankov et all present their results on time-related inactivation of coronaviruses in the ambient air at a range of climatic conditions.
The virus was highly robust and maintained a high survival rate of 63.5% at room temperatures (25 C, or 77 F) with a normal relative humidity of 79%. These microorganisms remained infectious for one hour after aerosolization. The virus decay was much stronger for the typical Middle Eastern temperature – which is hot and dry. At a high temperature (38 C, or 100 F) and a lower relative humidity (24%) the virus survival rate was 4.7% after one hour. The MERS-CoV virus survives better at an average room temperature and a higher relative humidity.1
In another study published by the Infectious Disease Societies of America, researchers explored the possible contribution of contaminated hospital air to MERS transmission by collecting air in two hospitals treating MERS-CoV patients. The presence of MERS-CoV was confirmed in four of seven air samples from two patients’ rooms, one patient’s restroom, and one common corridor.2
This information is consistent with airborne HVAC strategies set forth by the World Health Organization, which states “airborne transmission may be possible in specific circumstances and settings in which procedures or support treatments that generate aerosols are performed, i.e., endotracheal intubation, bronchoscopy, open suctioning, administration of nebulized treatment…”
Recommendations for controlling indoor air with ventilation and filtration:
Humidity and temperature control: There are ways of managing your relative humidity and temperature to prepare your indoor environment for reducing the spread of infectious disease. Coronaviruses tend to survive longer at relative humidity ranges between 20-30 percent, with a recommended range of between 40 and 70 percent to reduce change of survival. Higher temperatures have also been suggested to reduce the survival rate of these viruses, and one study suggests that keeping the temperature at 60 degrees C for more than sixty minutes is effective in inactivating most viruses.3
Negative Pressure Rooms: Negative pressure rooms are an isolation technique used in hospitals and medical centers to prevent cross-contamination from room to room. It includes ventilation that generates negative pressure – pressure that is lower than the surrounding pressures – to allow air to flow into the isolation room but not escape from it. As air will naturally flow from areas with higher pressure to areas with lower pressure, the process prevents contaminated air from leaving the room. Negative pressure is generated and maintained by a ventilation system that removes more exhaust air from the room than air is allowed into the room.4
HEPA Filtration: In some studies, it is mentioned that PM2.5 can be used as a transport vehicle for the virus and it is recommended to expand monitoring to individual indoor spaces. HEPA filters remove Most Penetrating Particle Sizes (MPPS) whose diameter is equal to 0.3 um. HEPA filtration is recommended because it can remove these particles from the air with an efficiency of 99.97%. Further, recent ASHREA guidelines for building operations is to consider portable room air cleaners with HEPA filters.5
Air Exchange: Personalized ventilation systems that supply 100% outdoor air, highly filtered, or UV disinfected air directly to an infected occupant’s breathing zone may be protective as shown by CFD analysis. However, there are no known field studies that justify the efficacy. Personalized ventilation may be effective against aerosols that travel both long distances as well as short-range routes.
There are many precautions to consider when trying to control the spread of infectious diseases. Most experts recommend using Personal Protective Equipment (PPE) like masks and gloves, as well as general hygiene best practices like washing your hands and using your elbow to cover any coughs or sneezes. However, some ventilation and filtration strategies may be an added precaution your building can take to do its part in containing the disease. It is important to consult governing agencies like the Center of Disease Control (CDC) and World Health Organization (WHO) before making any significant adjustments to your disease control measures.
Disclaimer: Our team does not claim to be medical professionals, but simply experts in building operations and management as it applies to creating a safe indoor environment for all. Our updates are based on the latest research available to the public, and we are constantly looking to improve the relevancy the content we share.