Healthcare & Dental


Using Air Purifiers to reduce the risk of virus infection in Healthcare Facilities & Dental Practices (COVID-19 Update) 

Healthcare workers, dentists, patients and staff need protection from airborne bacteria and viruses, mercury and disinfectants and there is now heightened concern over the specific spread of the Coronavirus disease (COVID-19). We have therefore put together this summary to assist health professionals who may be in the process of choosing suitable air purifiers for their premises.   

There are two key factors to consider when choosing a suitable air purifier for your treatment rooms, offices and public areas. 

Firstly, it is imperative that the air purifier contains the correct type of filter to be able to trap the smallest of airborne particles, especially those that may be harbouring viruses.
Secondly, the purifier must be powerful enough to recirculate the air through those filters up to ten times an hour to ensure airborne particles and Aerosols are being removed as quickly as possible. This factor is dictated by the air purifier's official CADR rating (more about this at the end). 

Key Factor 1 - Which Filter Grade?

To understand what filter grade is required it is vital to know about the particle size and distribution of the virus itself, there are two main airborne exposure types. 

(A) Transmission through large respiratory droplets up to 10 microns in diameter. 
These droplets are released when an infected person sneezes or coughs. Droplets in this size range tend to fall out of the air fairly quickly landing on surfaces up to two metres away. It is possible to catch the infection by touching those contaminated surfaces and in turn rubbing your eyes or touching your nose or mouth area. It is also possible for the virus to be transmitted by directly breathing in the droplets exhaled by an infected person if they sneeze or cough whilst you are standing within two metres of them.

(B) Transmission through smaller respiratory droplets up to 5 microns in diameter.
These tiny particles can stay airborne for hours and can travel long distances. As above, these are also created by coughing, sneezing and even talking. The COVID-19 virus itself is very small, around 0.16 microns in diameter, and is contained within these droplets. Some droplets are large enough for us to see, but many are invisible and range from around 0.5 micron to 15 microns. Studies have shown that droplets as small as 1.0 micron are capable of carrying enough virus to cause infections.

From a filtration point of view, the droplet is the particle that must be removed from the air as this is what the virus attaches itself to. The droplets are between 0.5 to 15 microns in diameter. The minimum recommended filter efficiency is a Hepa Filter certified to EN1822 and ISO29463 which removes at least 99.97% of particles at 0.3 microns. All genuine Hepa filters in grades H12 to H14 meet this performance criteria.

At the 0.3 microns particle size there is virtually no real performance difference between an H12, H13 or H14 Hepa Filter. Don't automatically assume that the highest grade H14 hepa filters will work best. In fact it is worth noting that in some cases choosing a higher grade H13 or H14 Hepa filter may actually be less beneficial. Higher grade filters use more dense filter materials which in turn slow down airflow. A low airflow (CADR) means less air changes an hour which in turn means it will take longer to fully recirculate the air through the filters. This can be especially relevant in a dental treatment room when trying to clean the air as quickly as possible between patients.  

Should my air purifier contain UV light?

In short, no. If your air purifier contains the correctly certified filtration as already described above then it does not require the addition of UV light to be effective in dealing with airborne Viruses and Bacteria. There are no ISO or EN standards for UV and although it has traditionally worked in static water tanks where over time it can eradicate particulate this is not the same as using it in an air purifier where the air flow is much too quick for the UV to have any effect. Also UV light often emits ozone, which itself is something best avoided in an air purifier. For peace of mind it is a good idea to choose an air purifier which has been officially certified as Ozone Friendly by the Air Resources Board.  

Key Factor 2 - Fallow Time Reduction. Clean Air Delivery Rate (CADR) This is key to choosing the correct purifier/s to reduce Fallow time. 

Having the correct filter fitted into your air purifier is one thing, but the speed at which the purifier can recirculate the air through the filter is quite another. Faster removal of airborne contamination is imperative to lower the risk of cross infection and to minimise the time it takes to cleanse the air between patient sessions. The most recent recommendation is to choose an air purifier which can provide ten air changes an hour within the dimensions of your specific treatment room and this leaves the room ready to accept new patients within twenty minutes.

To calculate if an air purifier is powerful enough to provide the correct number of air changes in your own room size you first need to know what the purifier's official CADR rating is. CADR stands for Clean Air Delivery Rate and is an officially verified measurement of exactly how much filtered air a purifier delivers. The CADR figure is normally quoted in m³/hr or ft/m³.

Note: CADR is not the same as a unit's air volume. Air volume is only a measurement of fan power with no filter installed, and is therefore always a higher (irrelevant) figure.
All things being equal, the higher the official CADR figure the quicker your room air will be purified. For an air purifier's claimed CADR figure to be credible it must be officially verified by AHAM, always look for the AHAM verified Logo. 

What CADR figure does my air purifier need to have to provide me with 10 Air Changes Per Hour? 

It's easy to calculate the minimum CADR figure required to achieve any number of air changes. 
For example, let's assume you have a treatment room with a floor area of 15m² and a ceiling height of 2.7m². You simply multiply those two figures together (15 x 2.7) and you get your room volume, which in this case would be 40.5m³. 

Now assuming you would like to achieve at least ten complete air changes an hour in this room size all you have to do is multiply your rooms volume (40.5m³) by the number of air changes you desire (10) and you will come to the minimum CADR figure your new air purifier needs to have, which in this case would be 405m³/hr (40.5 x 10). Ten air changes an hour equates to all the air in your whole room being completely filtered once every six minutes.  

The CADR figure of all our air purifiers can be found under the specifications tab on every product page.

Update: New Dental Fallow Time Calculator Launched.

Since we wrote the above article, a new Dental Fallow Time Calculator portal has launched. Built by digital consent platform Flynotes, supported by Practice Plan and Wesleyan, and endorsed by the Chief Dental Officer for England, the new tool complements the COVID-19 guidance published by the Faculty of General Dental Practice UK (FGDP) and the College of General Dentistry (CGDent), the recent update of which incorporates the Scottish Dental Clinical Effectiveness Programme (SDCEP) recommendations on fallow time.

Public Health England guidance currently recommends a fallow period of 60 minutes in a treatment room with less than 10 air changes per hour from the point that an aerosol-generating procedure is completed. The FGDP-CGDent guidance recommends that practitioners justify any decision to stray from this, record factors which allow reduction of the time, and include details in the clinical record for each patient.

The new Fallow Time Calculator is designed to facilitate this process, and is based on SDCEP’s multifactorial approach to determining fallow time. Set out in its recent publication, Mitigation of Aerosol Generating Procedures in Dentistry - A Rapid Review, this sets a ‘benchmark’ time of 15-30 minutes, which will vary dependent on the type and length of procedure, the employment of procedural mitigations such as high-volume suction and rubber dam, and the availability of environmental mitigations such as air ventilation.

Available at, the Fallow Time Calculator also offers a full audit trail, updated regularly in accordance with the guidelines, which practices can use to aid diary planning, allowing efficient patient treatment flows whilst ensuring necessary fallow periods are implemented. Register at

This new Fallow Time Calculator deviates from our example calculation above in that it now only accepts 50% of an air purifiers overall CADR rating as contributing towards the number of air changes. Therefore, assuming the fallow time calculator is accepted as the new benchmark, dental practices will now require their chosen air purifiers to possess CADR ratings twice as high as previously accepted if they are to meet the requirements of the new guidance.         

Need more Help?

One the link below you will find a selection of air purifiers all of which have been carefully selected to meet or exceed the standards outlined in this article. Sometimes however there is no substitute for just picking up the telephone and having a chat so please give us a call on 01207 507444 if you would like some good old fashioned human assistance, we do love to talk to our customers!