Frequently asked questions about viruses and air filtration

Yes. Studies have shown that person infected by respiratory viral infection such as Influenza can create droplets containing the virus by sneezing and coughing. These droplets can be both visible and invisible to the human eye. The droplets that are invisible can range from 0.5 to 15 micrometers. Studies on other common viruses suggest that a droplet of 1 micrometer can carry enough virus to cause an infection.

Yes. If you are recycling the air in your building to save energy, turn off the re-circulation and use 100% supply air. This will increase the ventilation supply rate. Viruses in the building are more likely to come from inside than outside. Fresh air dilutes the concentration and turning of the re-circulation prevents spread of virus throughout the building.

Yes. The effectiveness depends on the efficiency of the air filter. But as infectious droplets generally are larger than 1 micrometer the reduction of virus is significantly greater than the efficiency stated on an ePM1 or an EPA/HEPA air filter. The stated air filter efficiency on these filters is the minimum virus protection/reduction that you will get.

No. To prevent spread of airborne virus such as COVID-19, Camfil highly recommends ePM1 filters or higher. These filters will warrant 50% reduction of the virus over the filter and in most cases due to the size of droplet the reduction will be significantly higher. For some ePM2.5 filters the efficiency on 1-micron particles can be very limited.

It depends. Upgrading the filters to a higher filter class would increase the virus reduction over the filter step. However other considerations are important as well such as can the air handling unit handle the higher resistance over the air filter? Are seals and gaskets tight enough to justify the higher filter class? In general, one or two filter classes up will not cause a problem. Upgrading further than that requires correct measures.

No. Virus captured in the filter are strongly bound to the fibers in the filter media. 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 three days on open surfaces.

No, not necessarily. Stick to your regular maintenance protocol. Filters need to be changed regularly due to high pressure drop or other hygienic reasons. A virus outbreak does not affect your maintenance schedule.

Yes, apply use of air cleaners. If you have already turned off the re-circulation, increased the air flow and upgraded the filters to the maximum allowable filtration efficiency, then there is a possibility to use high quality re-circulation air cleaners. They are a very effective in improving overall air quality. The advantage of air cleaners and air purifiers is that a significantly higher filtration efficiency can be applied to rooms where it would otherwise be impossible. Through high air turnovers and high filtration efficiency it is possible to reduce the contamination in a room by 90% or more. It is a good idea to use room air cleaners in high risk areas and places where many people need to stay close together (such as waiting rooms, etc.)

With good hygienic protocol as recommended for used air filters. In general, there is very little chance for virus to stay active for an extended period in the air filter so the risk for infection when changing filters is low. However, general hygienic precautions should be taken when changing the filters to avoid exposure to harmful dust. Use full covered protective gear (long sleeves and full-length pants), gloves, respiratory face mask and protective glasses. Place the used filter in a plastic bag after taking it out of the air handler and seal the bag before moving the used filter. This is a general good practice and an important precaution for general air handling units. For special applications such as hospitals and laboratories special requirements may apply. Stick to any standard procedure that applies to your operation and only remove the full covered protective gear after leaving the ventilation room.

A good rule of thumb is, stick to your regular maintenance schedule. If you don’t want to upgrade your protection, there is no reason for changing your filters because of COVID-19. You should also not delay the planned filter change. Running too long on filters may cause your air flow to go down, energy cost to go up and other hygienic aspects of running the filters too long may come into play (like smell, mold growth etc.).

No. The protection level of the filtration system is determined based on the overall efficiency of all filter steps. A single-stage filtration can provide a higher efficiency than a dual-stage filtration if a higher filter class is used in this step. The purpose of dual-stage filtration is mainly to prolong the life of expensive high efficiency final filters.