HEALTHCARE ESTATES 2022 KEYNOTES – ENGINEERING
inhale more of those short-range aerosols. We can get large droplets that can have direct deposition, but these are not that likely to hit you. We then have deposition onto surfaces, and people potentially touching things.” How important this was depended both on the environment, and the duration of exposure. Inhalation exposure was, the speaker stressed, key, and pathogens can be transported more readily in air. The Professor noted: “It’s complex. We’ve got fluid dynamics, chemistry, and microbiology to consider here, plus – really importantly – human characteristics, because while we can do all the physics to the nth degree, people then come along and mess it all up. We all breathe out particles when we are not even thinking about it. Some people, of course, breathe out more than others. We don’t know why. We do know, however, that we breathe out more when we are louder – when we sing, shout, or cough.” There were, however, ‘big ranges’ in the number of particles exhaled and inhaled by different individuals, which made interpreting the associated data difficult. Showing a graph of a log scale, she
said: “The graph basically tells us that the majority of particles we breathe out are actually really small – typically under 10 microns in diameter. The smallest human- visible particle is about 40 microns, so we can’t actually see much of what we breathe out – what we traditionally term droplets. Some of these very small particles contain virus, which is considerably harder to measure.”
US measuring system The speaker explained that a group of US scientists had a special instrument which could measure viral RNA if an individual put their head into a ‘cone’ and, for example, breathed, or sang into it. She said: “Surprisingly, the scientists with this device typically see up to five times more of the viral RNA in the smallest aerosols than in the bigger droplets. This tells us the small things matter, and the same evidence comes for ‘flu. You also see big variations, although people wearing a mask do emit less into the environment – fairly simple physics really.” Particles containing, for example, a virus, sometimes deposited on surfaces. Prof. Noakes said: “The graph on the left is comparing what might end up on people’s hands from touching surfaces in a single room versus a multi-bed room, where in fact you do you get more on your hands. Although not ‘rocket science’, it highlights that anything dispersed into the air is more readily dispersed onto surfaces close to other patients, and that while you might not think that a surface is contaminated, it will be.” The Professor next showed a slide of a
study focusing on a COVID-19 outbreak in Korea. This clearly demonstrated the
November 2022 Health Estate Journal 49
significance of movement of air between spaces. Here a bathroom ventilation system was not functioning correctly – it was under positive rather than negative pressure, and thus pushing air from the bathroom into a central zone and ward spaces.
Prevalence of natural ventilation “So,” she said, “this is a complex picture. Lots of our hospitals are naturally ventilated, and we know they are hugely variable; it depends on what you do, and the wind.” Showing another chart demonstrating ‘Variation in natural ventilation’, she said: “So on the left, the red bars are when you’ve got the windows closed, and the dark blue bars when they are open; this is a Nightingale ward. Unsurprisingly,” she added, “this is a ‘leaky ward’ – you get a much higher exposure when you close the windows; about four times the amount when you close the windows to when they are open.”
Another chart showed measurements
from a study of naturally ventilated wards in Peru. This highlighted the massive potential variability with natural ventilation, depending on the wind direction, whether the wind is blowing, and any temperature difference. Prof. Noakes said: “So, we know our buildings, and that we have a raft of different risk factors – environmental risk factors influence transmission, but so do human factors. While we can’t control them all, our buildings have a major impact in setting out the conditions, and influencing our interactions. The building design determines whether spaces are crowded, any pinch points, and whether people can distance a little bit more.
Human behaviour’s influence “Given that buildings can’t manage all the behaviour, it’s key to recognise that while we can take this to a point with engineering, we then need the human
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