One Take #2 - Experimental analysis to quantify inactivation of microorganisms by Far-UVC

Imagine a technology that could silently work in the background, destroying harmful microbes in the air we breathe without harming us. That's the promise of Far-UVC light at 222 nanometers, and groundbreaking room-scale research just brought this closer to reality.

Hospital-acquired infections alone cost the NHS £2.7 billion annually and affect hundreds of thousands of patients. While proper ventilation remains our first defense against airborne pathogens like TB, influenza, and COVID-19, the harsh truth is that many buildings struggle to meet modern ventilation standards. Retrofitting these structures often proves prohibitively expensive or physically impossible, creating an urgent need for complementary solutions.

Far-UVC technology stands out because, unlike traditional ultraviolet light, current evidence suggests it doesn't harm human skin or eyes when used properly. This means it could potentially operate in occupied rooms—a massive advantage over conventional UV systems. The University of Leeds study demonstrated remarkable results in a hospital room-sized chamber, with bacterial reductions of up to 97.8% using five Far-UVC lamps. Most impressively, the technology showed greatest benefit in poorly ventilated spaces, exactly where alternative solutions are most needed.

The research tested various scenarios, changing ventilation rates and airflow patterns while continuously introducing aerosolized bacteria to simulate a person shedding pathogens. Even at low ventilation rates of 1.5 air changes per hour, bacteria levels dropped to barely detectable amounts with five lamps. While further research is needed to test effectiveness against viruses in real-world settings, these results paint a promising picture of Far-UVC as a powerful new tool in our infection control arsenal. Could this technology transform how we protect vulnerable spaces like hospitals, schools, and nursing homes? The evidence suggests the future looks bright—or should we say, ultraviolet.

https://www.sciencedirect.com/science/article/abs/pii/S0360132325002161

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Chapters

• 0:00 Introduction to Air Quality Matters
• 0:24 Far-UVC Technology Basics
• 1:50 Experimental Chamber Setup
• 3:36 Key Results and Findings
• 7:15 Implications and Future Research
• 10:16 Conclusion and Takeaways

Transcript

Speaker 1: 0:00

Welcome back to Air Quality Matters and One Take One Take my take on a paper or report on air quality, ventilation or the built environment. It's one take in that it's well, in one take, hopefully and tries to summarise for you the scientific perspective on something in well, usually 10 minutes or less. Because who has the time to read all these amazing documents, right? Because who has the time to read all these amazing documents, right? This week I'm looking at a paper called Experimental Analysis to Quantify Inactivation of Microorganisms by Far UVC Irradiation in Indoor Environments. It's by Waseem Huar et al. This paper is all about a technology called Far-UVC for those that don't know it specifically at a 222 nanometer wavelength, and managing exposure to airborne microorganisms is pretty critical, especially in places like hospitals and other high-risk environments like schools, for example.

Speaker 1: 1:28

Hospital-acquired infections, for instance, cost the NHS in the UK a staggering amount over 2.7 billion a year back in 2016-2017, affecting hundreds of thousands of people, and COVID-19, as we all know, massively amplified this problem. We've known for ages that diseases like TB, measles, influenza and, yes, COVID-19, can spread through the air. Ventilation is, of course, our first line of defence. It's a cornerstone of control. But here's the rub Many buildings, even in healthcare, don't meet current ventilation standards, and upgrading them can be eye-wateringly expensive and just practically very difficult. So people are increasingly looking at air cleaning technologies to give an extra layer of protection without having to rip out and replace entire ventilation systems. Some of these, like HEPA filters or traditional UVC light, are well established, but far UVC is one of the newer kids on the block and it's showing a lot of promise. The really interesting thing about far UVC, particularly the 222 wavelength type we're talking about here, is that current evidence suggests it doesn't cause the same kind of harm to our skin and eyes as traditional UVC, as long as it's used within safety guidelines. This is a big deal because it means it could potentially be used in occupied rooms, which opens up a whole lot of possibilities. These krypton chloride lamps they use are filtered to cut out the more hazardous wavelengths. There's been a fair bit of lab work showing far UVC can inactivate a range of bugs, including SARS-CoV-2 and influenza, both in the air and on surfaces. But what this paper does and it builds on previous work by the same authors is take it to the full room scale, experimental chamber level. That's important because what happens in a small box in a lab doesn't always translate to a real room.

Speaker 1: 3:54

So what did these researchers actually do? They set up a controlled bioaerosol chamber at the University of Leeds about the same size as a single bed hospital room, so roughly 32 metres cubed. They made sure the air coming in was HEPA filtered so it was clean to start with, and then they used either one or five far UVC lamps these krypton chloride ones, mounted near the ceiling. They then aerosolised or sprayed two types of bacteria into the room Staphylococcus aureus you might know its cousin MRSA and another one I'm not going to try and pronounce. Both are pretty relevant hospital pathogens. They created a scenario of continuous contamination, which is more realistic if you think about someone in a room consistently shedding. They then measured the concentrations of these airborne bacteria under different conditions, varying the ventilation rates from low levels of about one and a half air changes per hour or air changes up to about nine five, changing how the air flowed through the room, like high inlet, low outlet or low outlet, high outlet, and even looking at inactivation over shorter distances. Air samples were taken before far UVC lamps were turned on and then again after they'd been running for a while to let things stabilize. They also looked at how many microbes settled onto the surfaces.

Speaker 1: 5:34

Alright, so what were the big takeaways? What did they find? Well, first off, the far UVC lamps significantly reduced the steady state concentrations of these airborne bacteria. We're talking pretty hefty reductions, for example the Staphylococcus aura. At three air changes per hour one far UVC lamp cut the bacterial load by a mean of 95.5%, and five lamps pushed that to 97.8%. So it definitely works to lower the microbial load in the air. Now the number of lamps, and therefore the UVC intensity, clearly mattered. Five lamps generally gave a higher reduction than just one. That makes sense. More UVC light, more inactivation.

Speaker 1: 6:25

The ventilation rate also played a really interesting role. The relative benefits of far UVC was greater at lower ventilation rates. So at one and a half air changes the reduction of the Staphylococcus aureus was over 94.6% with one lamp and even better with five. In fact, with the five lamps they could barely detect any bacteria at all. But when they cranked up the ventilation to nine air changes, the reduction with one lamp was around 66.3% and 91.9% with five lamps.

Speaker 1: 7:06

This isn't because the far UVC stopped working as well. It's more that the high ventilation rates, the ventilation itself, is already removing a lot of airborne particles. So the additional benefit you measure from the far UVC is relatively less. Plus, at higher air speeds the microbes spend less time in the UVC field, I suppose. What about different airflow patterns? You know where the air comes in and goes out in different ways. They tested that too and while there were some small variations, the overall takeaway was that ventilation rates seem to be more important factor than the specific ventilation regime.

Speaker 1: 7:49

So what does all this mean? Why is the paper important? I think the biggest thing is that these are room-scale experiments under continuous contamination conditions, which is a step up from the smaller lab tests and gets us a bit closer to understanding real-world potential. It shows that far UVC isn't just a theoretical concept. It can tangibly reduce airborne pathogen load in a room. This technology could be a really valuable tool, especially in situations where traditional ventilation upgrades are challenging or super expensive Think older buildings or spaces that need a quick enhancement of air hygiene.

Speaker 1: 8:34

One of the critical points the paper touches on and it's often a concern of UVC is ozone generation. These lamps can produce small amounts of ozone. The researchers did some calculations and found that the ozone production rate was in line with other studies, that the ozone production rate was in line with other studies. What's key here is their conclusion that it's likely feasible to implement far UVC to get a good microbial inactivation without posing unacceptable risks from ozone, especially when you consider ventilation rates. It's also clear that far UVC isn't necessarily a standalone magic bullet. The authors suggest that in real life you'd likely pair it with existing ventilation and possibly filtration systems as well, to get the best overall effect. It's about adding another layer to our infection control strategies. Careful design, like the number and position of lamps, could be really crucial.

Speaker 1: 9:35

Now, the authors are good scientists, so they also point out the limitations of the studies. They only tested two types of bacteria and under specific temperature and humidity conditions. The way they aerosolized the bacteria is standard for lab studies but might not practically replicate human respiratory aerosols, and their chamber was pretty well mixed. Real rooms can have a more complex airflow. So they acknowledge that more research is needed to explore the effectiveness against viruses in different environments with different aerosol types and in more realistic, less controlled scenarios.

Speaker 1: 10:12

To wrap it up, what's the main takeaways here? To wrap it up, what's the main takeaways here? The study provides pretty strong evidence that far UVC technology, specifically in the 222 wavelength band has substantial potentials to reduce the concentration of airborne microorganisms in indoor settings. It works effectively against relevant bacteria under various ventilation conditions and even shows promise to reducing surface contamination and for short-range applications. The effectiveness generally increases with more lamps and is particularly noticeable as an additional measure when ventilation rates are lower. While there are things to consider like ozone management and optimization of lamp placement, the findings are really encouraging. I reckon it paves the way for future work to see how this performs in real world scenarios. Definitely a technology to keep an eye on as we continue to grapple with improving the air quality indoors and the air we breathe. Hope you found that interesting. I'll put the links in the show notes and on the social media posts as usual. Thanks for listening. I'll see you again next week.