In a scientific debate, WHO has acknowledged that in the case of COVID-19, airborne transmission could not be ruled out in crowded, closed or poorly ventilated settings. Scientists across the world are looking for more evidence as it may affect many guidelines in the crowded indoor environment. Previously, WHO has recognized the studies and evidence detailing the transmission of COVID-19 from symptomatic people to others who are in close contact through respiratory droplets, either by direct contact with the infected person or by close contact with contaminated objects and surfaces.
The size of the particle that needs to be filtered in the indoor environment defines the choice or selection of the efficiency of the air filtration solution. For example, pollen or bacteria seems gigantic in size when compared with the COVID-19 virus, hence the protection that is good enough for seasonal allergies, may not be sufficient to fight against harmful pathogens like the COVID-19 virus. To compare it further with the human hair that is 60 to 120 microns in diameter will give a fair understanding of how small the COVID-19 virus is.
What can be done?
Improving the ventilation system, managing the airflow and air filtration is the key to reduce the spread of COVID-19 in the indoor environment.
1. Increase the flow of outside air
- supply clean outdoor air
- increase outdoor air ventilation rates
- minimise recirculating air
Where possible determine if the flow of outside air can be increased and turn off or reduce the recirculation air. Modifications in the HVAC system such as installing an airflow control system that will enable the fresh air supply to be maximized and the recirculation air to be minimized. If you need to use recirculation air, upgrade to high efficiency filters that are capable of capturing particles <1 micron in size (ISO ePM1 80% and above). Along with this ensure that your indoor fan motor in HVAC has sufficient power to handle the upgrade.
2. Use air filters with ISO ePM1 filter class
- high efficiency air filtration, subject to fan capacity limitations
- portable room air cleaners/purifiers
- follow regular maintenance protocol
- humidity control
The high efficiency air filter can trap the particles responsible for the spread of the virus and they become inactive while captured on the filter membrane. Upgrading to high efficiency filter depends on the pollution level in the air. Higher quality filter may require a pre-filter to ensure the reasonable operational life time and fans should be able to handle the increased pressure loss over the filter step.
Camfil recommends an ISO ePM1 filter class according to ISO 16890 (ePM1 80% or higher) for HVAC systems with air handling units (AHUs), however, due to increased resistance to airflow and space restrictions, this may not be practical for every commercial HVAC system. Consider using air cleaners for fast and easy retrofit in case of a sub-standard ventilation system for improvement in air filtration. It is also a way to rapidly boost the air quality of an already good functioning system when there is an increased risk that demands even better protection. An air filtration expert can do the proper analysis and suggest the solution based on the indoor enlivenment and existing HVAC system to minimize the impact of harmful pathogens such as COVID-19.
The efficiency of high performance air filters (HEPA filters) is measured at MPPS (most penetrating particle size) which means this is the lowest efficiency of the filter. For smaller or larger particles that filter will perform even better. MPPS is typically between 0,1-0,2 micrometers in size. Bacteria and viruses are often smaller than that but typically attach themselves to larger particles. It’s also important to understand that air filters do not actively kill living organisms. They capture and hold them within the matrix of the filter. Once the virus is captured it will stay in the air filter and eventually dry out and die (refers to as inactive). Studies on COVID-19 virus indicates that the virus does not survive longer than 3 days on open surfaces. The following diagrams will explain the efficiency of the selected air filtration in the fight against submicron particles such as vehicle emissions, bacteria, viruses, and other harmful pollutants.
Netherlands
