Can Air Purifiers save you and your dental practice from COVID-19?


As we all stay at home protecting our NHS and saving lives during the COVID-19 pandemic, others like dentists are seeking solutions that will allow them to re-open and limit unnecessary exposure to contaminated aerosols.


Professional Facebook groups and other dentistry forums are being swamped with questions about the use of Air Purifiers in dental surgeries and whether this is a solution worth looking at?

🦠 Size does matter…

Some Air purifiers with HEPA filtration may capture particles the size of (and far smaller than) the virus that causes COVID-19, and many readers have asked whether air purifiers can help protect against infection. The answer is yes, in theory… though it is not that simple.


It is known that virus that causes COVID-19 is approximately 0.125 micron (125 nanometers) in diameter. It falls squarely within the particle-size range of some HEPA filters with extraordinary efficiency: 0.01 micron (10 nanometers) and above. But many air purifiers sold on UK market are not capable of filtering particles below 0.3 micron and therefore could not capture airborne coronaviruses.


In order for the filtration to have any impact on the transmission of infectious diseases, these have to be correctly installed and maintained to treat recirculated air efficiently. Filters have to be appropriately designed for the building in which they are used. More importantly, in most buildings and most situations, filters may be considerably less effective than other infection control measures, use of correct PPE, social distancing, isolation of known cases, and hand-washing.

So should you use high efficiency filters in your practice? And what filters should you use?

Correctly installed higher efficiency filters can remove particles of a relevant size depending on their installed capture efficiency. However, High-efficiency filters may be appropriate for your building, but they can also be counterproductive. A high-efficiency filter may load with dust and particles very quickly, therefore requiring more frequent change. If filters are not replaced when needed, this may result in contaminated air bypassing the filter and diminish the amount of air supplied into the environment, making the filters less effective.

I know that hospitals have good filtration, why don’t we all just use systems like these?

Hospitals (and many other healthcare facilities) have specially designed mechanical systems that can accommodate the required levels of filtration. They often incorporate other systems and control strategies (e.g., UV lamps, humidifiers) to maximise the benefit from filtration. Most importantly, they have dedicated competent staff to operate and maintain this equipment.

Ventilation in hospital settings (especially operating theatres) needs to meet strict design and performance specifications in line with HTM - 03-01.

Principles of ventilation in healthcare settings during COVID-19 :

  • Establishing a clean airflow path (a desired airflow path is from a clean to a less clean area). This is not a new thing, and many of you will be familiar with this requirement from the infection prevention point of view.

  • It is recommended that any ventilation or air conditioning system that normally runs with a recirculation mode should now be set up to run on full outside air where this is possible (working as an extract). For example, special isolation rooms in hospitals are required to have – a ventilation system that prevents the uncontrolled escape of infectious aerosols from the room to adjacent areas. It can also provide a degree of dilution of infectious aerosols in the room for the safety of staff and visitors.

  • Recirculation of air between spaces, rooms or zones occupied by different people or used for different purposes (waiting rooms, staff rooms) should be avoided. 

Is there any additional risk associated with air purifiers?

All ventilation systems should conform to the principles set out in the Health and Safety Commission’s Approved Code of Practice and guidance document ‘Legionnaires’ disease: the control of Legionella bacteria in water systems’ (commonly known as L8), and Health Technical Memorandum 04-01 – ‘The control of Legionella, hygiene, “safe” hot water, cold water and drinking water systems.’


Design provision must be made for the subsequent safe handling of contaminated HEPA filters by staff. Filters fitted to remove hazardous substances from the recirculated room air are classed as hazardous waste and should be handled and disposed of accordingly (see also Health Technical Memorandum 07-01 – ‘Safe management of healthcare waste’).

Validation of the performance of the filter should be in place when installing the units and subsequently and at regular frequency.

Summary

Suitably designed, sufficiently sized and well placed an air purifier, will help dilute indoor contaminants including virus particles.


  • Air purifiers will capture viruses, but won’t destroy them. The virus may remain alive inside the filter for a considerable amount of time.

  • Air purifiers should be well maintained and filters regularly replaced. The efficacy of these units is directly related to their cleanliness. In this respect, the manufacturer’s instructions regarding service/maintenance and UV lamp (if fitted) and filter replacement should be closely followed.

  • Records of inspection and maintenance activities should be kept for at least five years.

  • Units that have been used in isolation rooms or areas containing infective patients will need to be fumigated before being used in other locations or returned to store.

  • Air quality sampling that includes microbiological testing may help you validate the efficiency of the device

  • If you do decide to buy an Air Purifier, make sure that it comes from a reputable source (avoid Amazon or eBay, comes with good maintenance instructions (in English).


IMPORTANT


HTM03-01 “If the ventilation plant has been installed to dilute or contain harmful substances, its failure may expose people to unacceptable levels of contamination. Proven breaches of the statutory requirements can result in prosecution and may also give rise to a civil suit against the operators.”

Regards

Sylwia Leszkiewicz MWSOC

Director & Independent Consultant

E: sylwia.le@thefirstprinciple.co.uk

Reference:

Chartered Institution Of Building Services Engineers - CIBSE Journal

Chartered Institution Of Building Services Engineers - CIBSE Guide A & B

Health Technical Memorandum 03-01

Health Technical Memorandum 04-01

Critical Care Units Planing and Design HBN04-02

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