THE BRIEFING
An enlightening conversation UV expert Dr Normand Brais recently met with AIRAH’s Infection Control and Operating Theatre Practices STG. AIRAH’s special technical groups (STGs) bring together experts in specific areas of HVAC&R to develop technically accurate, unbiased information that can then be disseminated to other AIRAH members and the wider industry. As part of the Institute’s response to the pandemic, the Infection Control and Operating Theatre Practices STG is developing advice for operating theatres. To inform this work, the STG invited Dr Normand Brais to give a virtual presentation on UV-C and how it can prevent the spread of COVID-19. Dr Brais holds a mechanical engineering degree and a PhD in nuclear engineering from Polytechnique, University of Montreal. After graduating he was appointed professor at the Energy Institute of Polytechnique, and in 1995 he founded Sanuvox Technologies, which is now a worldwide UV disinfection specialist.
WHERE UV FITS IN Dr Brais began the presentation by outlining the high-level approaches to creating a safe indoor environment: enhanced filtration, dilution ventilation, air and surface conditioning (including UV-C), and occupancy management. Focusing on UV-C, Dr Brais noted that, before COVID, UV light was mainly used for disinfecting water. But since the pandemic began – and especially since aerosols were acknowledged as a primary pathway for the virus – people have been looking at how it could be used on air. The typical droplet size for SARS-CoV-2 loaded aerosols is 5–10μm, and the naked virus on average measures just 0.08–0.12μm. “A droplet of one micron can contain sufficient load to contaminate a person,” said Dr Brais. “If you look at droplets of that size, they will stay airborne almost all day long.” Next, Dr Brais looked at different levels of filters and how these prevent the spread of the virus. He proposed that 18 J U N E –J U LY 2021 • ECO L I B R I U M
using a combination of MERV-13 filters and UV-C would offer the best “bang for buck” – restricting the spread of pathogens without inordinately increasing operating costs.
TRICKS OF THE LIGHT UV light damages the DNA/ RNA of microorganisms, so they cannot reproduce. And because UV-C has been applied to water for more than 50 years, there is a large amount of data on how effective it is in inactivating microorganisms. Among bio‑contaminants, SARS-CoV-2 is relatively susceptible to UV light, but as Dr Brais said, “the question is how to apply it”. Various approaches were discussed, including in-duct UV-C, coil disinfection, automated and manual surface disinfection, and upper air UVGI. Dr Brais explained that on some surfaces, such as metal, plastic and wood, UV light is very effective; on others, such as fabrics and textured surfaces, nooks, crannies and micro-canyons offer places for microorganisms to hide. Obviously, when installing in-duct UV, air velocity must also be considered using specially developed software. When it comes to operating theatres, where higher efficiency HEPA filters are generally installed, Dr Brais recognised that the benefits of installing UV-C may not justify the cost. But he also shared his experiences with some specific applications, such as in vitro fertilisation, where UV-C did make a difference on top of HEPA filters.
NEXT STEPS One issue the STG flagged is the lack of independent third-party verification for technologies being marketed around COVID-19.
Dr Normand Brais.
The Centers for Disease Control and Prevention (CDC) recommends using UVGI “as a supplemental treatment to inactivate SARS-CoV-2 when options for increasing room ventilation and filtration are limited”, and ASHRAE has also published material acknowledging its uses. But there is still a gap when it comes to standards. Although standards exist for UV disinfection of water, they have not yet been established for air disinfection, so designers and end-users must often rely on manufacturers’ claims. Nor is there a body or organisation that certifies UV installations. As Dr Brais pointed out, these things are very much needed – and the pandemic may offer the perfect conditions for highlighting this gap and developing such a standard and establishing a certifying body. With the valuable input of Dr Brais, the STG is refining its advice for release. ❚
Need to know For more information on AIRAH’s Infection Control and Operating Theatre Practices STG and other STGs, go to www.airah.org.au/stgs
