Are you using CEN ISO tested air filters as the best tested solution for the removal of infectious airborne viruses and bacterial particles from air inside buildings?

When you walk into the room, how do you know that you are not breathing in viruses, bacteria, or other chemical and toxic particles that are indoors or come in unfiltered from outside air? It may seem as though you are powerless in such a situation. After all, to what extent can you control the indoor air quality at home, in school or at offices? But by being educated, you can be empowered. Learn about what makes the difference between being healthy and productive or tired and even sick so you can be one step closer to stop breathing contaminated air.

The air we breathe into our lungs is loaded with airborne particles of all shapes, sizes and compositions. While some are biological, such as pollen, spores, bacteria and virus, Others are chemical, such as toxic fine combustion particles found in city traffic air pollution.

The COVID-19 pandemic has focused attention on using air filtration to clean air inside buildings by removing airborne bio-particles, thus reducing the risk of infection.

Small airborne particles in the size 1 micron and below (called PM1), tend to be of concern because they can penetrate deeply into our bodies. Bio-particles like bacteria and viruses can deposit in our nose, and sinus and even reach deep into the lungs, where they cause deadly infections.

Figure 1: ©Peter Dyment, Camfil

Air filtration is the only air-cleaning technology that can protect people against infectious airborne particles by removing them from the air stream. General ventilation air filters are tested for particle removal efficiency by the current European and global test standard EN ISO 16890:2016. For higher filtration efficiencies needed in critical applications, HEPA filters can be used and are tested to EN1822:2019.

In life science laboratories HEPA filters are used to contain viruses and bacteria, H14 class filters with 99,995% efficiency at maximum penetrating particle size (MPPS) would generally be used. Similarly tested H14 class filters can be found in standalone high specification air cleaners and air purifiers.

Many other new technologies have the potential to treat air or rather the airborne infectious particles, but for most, their efficacy has yet to be properly tested. Any proposed new technology should be performance tested by an approved and peer-reviewed CEN or ISO technical standard so the resulting test data can be reproduced in controlled conditions.

There are many technologies such as UV light, photocatalytic oxidation, pulsed light, ionisation, ozone, thermal, microwaves, plasma, corona discharge, ultrasonification, chemical disinfection, free radicals, or plant biology based technology.

Using these emerging technologies, airborne bio-particles are usually subjected to varying doses of radiation or chemical agent depending on the technology employed. If particles are not removed, care must be taken to ensure they have the required deactivation dose for each particle.

It is not possible to ‘kill’ a virus because it is not alive in the true sense of the word. A virus is a bundle of genetic material that can propagate by penetrating and infecting living host cells.

A virus such as COVID-19 is very small (typically about 0,12 to 0,16 micron in diameter) and usually is enclosed in a liquid envelope when it is projected as an aerosol droplet by an infected person into the indoor air space. Larger particles up to 5 microns can stay airborne for hours and, unless removed from the air by air filtration, will continue to pose a risk in the breathing zone.

A recent study at Addenbrookes NHS hospital in the United Kingdom1 in a fully occupied COVID-19 ward indicates that the airborne infection is principally transported in the particles size 1 micron and above. This would indicate an increased role for PM1 rated ISO16890 tested HVAC filters, and that a greater use of clean filtered recirculation air would be beneficial to building occupant health.

Without a suitable air filter to remove clouds of particles in the air they can remain suspended and thus inhaled. In a world where the threat of air pollution and COVID-19 infection is now a daily challenge and a worry for most people then probably they would not be comfortable breathing unfiltered air inside our occupied offices or many busy public buildings.

Indoor spaces found in schools, hospitals and crowded offices are places where this concern over breathing in airborne viruses and bacteria is now brought into sharp focus.

Figure 2: ©Peter Dyment, Camfil

Airborne particles unless filtered out are free to drop to a surface where deposited bio-particles on surfaces may facilitate contact infection when touched by people. This is why regular surface cleaning can be important.

One way to be reassured about breathing in air inside buildings is to use an air monitor to measure the concentrations of PM1 and PM2.5 size particles and how they vary over time. Air monitoring technology has significantly reduced in cost and are effective to check the concentration of PM2.5 for example and see whether it is much above or below the World Health Organization concentration guidance of 5mg/m3 (annual mean WHO 2021).

Air sampling and analysis can confirm the presence of specific viruses and bacteria in the particles at different sizes. They should be used more frequently in places where there is a high risk of infection.

Carbon dioxide (CO2) can also be monitored to indicate indoor space occupancy and areas of poor ventilation. Where peaking CO2 and PM2.5 coincide, that could indicate raised levels of bio-particles, some of which could be infectious. Over time and with experience it is possible to learn to characterise the sources of particles and match them to activities in and around the indoor space.

Bio-sampling of the air and particle size/composition analysis is a better approach to a particle-based infection problem.

Where appropriate, the main system air handling unit air filtration can be supplemented by standalone air cleaners. This combination gives full building clean air capability.

Air monitors can be used to prove delivery of the clean air and in some cases control the operation of the ventilation plant itself.

Building occupants have had to learn a lot over the last year and a half about washing hands, maintaining social distance, cleaning surfaces, wearing face masks (air filters for your face) PPE, and now they are learning about the benefits of air filtration for clean healthy indoor air.

We are all still learning you cannot take clean air for granted if you want to be comfortable and safe with minimum risk, in your indoor environment, at home, at work or in any other buildings.





Mr Peter Dyment

Technical Manager, Air Quality and Building Energy Consultant