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UV air purification solutions should not be considered a “magic solution” for improved air quality, even with research showing their effectiveness to inactivate microorganisms such as viruses in certain situations

A leading IAQ expert has warned that while Germicidal UV (GUV) light technologies can provide an effective solution to manage airborne pathogens, they are not a direct replacement for effective ventilation.

Professor Catherine Noakes, a member of the government’s Scientific Advisory Group for Emergencies (SAGE), made the comments during a recent BESA webinar looking at air cleaning systems such as those using UV light.  Professor Catherine Noakes said GUV was shown in some testing to be an effective tool for managing exposure risks to microorganisms such as viruses in certain situations. However, UV systems were not a ‘magical’ solution for ensuring good IAQ on their own.

Effective management of the virus would therefore require a range of factors and user behaviours to be considered when introducing GUV or air management systems. This would ideally involve combining a range of technologies such as ventilation and air cleaners with non-mechanical measures such as using face coverings and cleaning regimes to mitigate risks.

Professor Noakes, who is also deputy director of the Leeds Institute for Fluid Dynamics, said, “Ventilation is part of mitigation and GUV is part of that answer. But it can’t solve a fundamentally unventilated space.  If you have a poorly ventilated space, GUV might reduce your risk of pathogen exposure, but it won’t deal with poorly ventilated spaces.”

Ventilation vs air cleaning

As opposed to focusing on debates pitting the effectiveness of UV solutions directly against ventilation systems, Professor Noakes said it was important to improve public and industry awareness that these technologies served very different purposes.

She added that ventilation has multiple purposes, such as diluting and removing contaminants that include exhaled CO2.

High levels of CO2 have been linked to negatively impacting concentration and productivity in building occupants, as well as being used as an indicator of poor airflow that might increase infection risks from a virus such as Covid-19. Ventilation systems that have been properly installed can address build-up of CO2 levels, while also having a direct impact thermal comfort and humidity, the webinar heard.

Professor Noakes said, “So there are a lot of reasons why we need ventilation regardless of Covid.”

“Air cleaning is only about contaminants.  Some will only remove certain contaminants and UVC systems is one of those.  It is only a biological mechanism.”

Professor Noakes said that UV air cleaning solutions were believed to be effective at addressing the spread of pathogens such as Covid-19 at longer ranges as the virus is carried in aerosols.  However, their impact was expected to be more limited at reducing the risk of closer range infection.

She said, “Particularly when you get within about a metre of somebody, your exposure is really dominated by the physics of the airflow in that range and unless you have an air scrubber that is right next to you.  You are unlikely to have an impact on that transmission through the air cleaner.”

Air cleaners should therefore be seen as one potential route for mitigating the spread of a virus, Professor Noakes added.

She said, “It’s not a case of, ‘we have put this in and we are now safe’. It’s about reducing risk rather than removing risk.”

‘Hierarchy of controls’

The BESA webinar heard that any effective strategy of using UV solutions for air cleaning should consider the principle of the ‘hierarchy of controls’ that considers a range of engineering and wider safety measures to limit infection risk.  Professor Noakes said engineering controls such as GUV systems or ventilation were placed in the middle of this pyramid of measures to manage different infection risk levels.

She said, “They are not as effective as lockdowns [at the top of the pyramid], but they are potentially more effective than some of the administrative controls we can use. This is because they do not rely quite so much on human behaviour, so if engineering solutions are designed well, they are there as background.”

Administrative controls can include cleaning regimes and signage to encourage behaviours such as social distancing and mask use.

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