ACR Journal

April | May 2021 VENTILATION 32 Can Natural Ventilation provide the safe Indoor Environment we need? Volume 7 No.3 The importance of ventilation cannot be overstated when it comes to the safe return to schools and workplaces; it is singularly the most important factor that separates safe work environments from super spreader events. This view is almost unanimously supported by the scientific community and Scientific Advisory Group for Emergencies (SAGE) advisors such as Professor Cath Noakes, an ACR Journal contributor. There is no such thing as a safe distance indoors if the space is not adequately ventilated. The nature of buoyancy-driven air movement in enclosed and unventilated spaces is such that each breath ends up being carried to the furthest reaches of the room at some point. It will, of course, be diluted. Still, suppose we are sitting in the same room with an infected person. In that case, we are likely to receive an infectious dose of a virus at some point, regardless of masks, screens or two metre distancing - although we still do not fully understand what an e„ective dose is, nor how much this can vary from person to person. Ventilation Rates Any ventilation method capable of the e„ective removal of stale and potentially infected air while providing fresh air to the occupants at a rate of about 10 litres per Tom Lipinski, Founder and Technical Director of natural ventilation specialists, Ventive, shares a recent study illustrating the possible transmission of viruses with different ventilation systems. second per person should improve safety indoors and significantly reduce the risk of virus transmission. But – are all these methods as e„ective as each other at reducing the risk of infection? If we are designing an oŠce, building, or a school, how do we make it pandemic resistant and future-proof? Would we want to design a single ventilation measure that can handle ‘normal’ requirements but can adapt to suit emergency requirements such as pandemics? Or would we need a suite of measures, one for maintaining basic Indoor Air Quality and one for emergency response? An architect or a mechanical and electrical engineer would want to have answers to these questions. As much as there is consensus that adequate ventilation is key to ensuring a safe indoor environment, there is less of a consensus, and even less data, to help us understand the impact of various ventilation measures on transmission risk levels. Professor Ben Jones from Nottingham University states that we need a ventilation rate of 210 l/s for every infected person to mitigate the risk of infection 1 . Therefore, if we are in a meeting room of five designed to ventilate at 10 l/s/person with one positive colleague, we would all become infected. His insight provides little in the way of recommended measures to achieve this. Professor Paul Linden from Cambridge University states that displacement ventilation provides the safest indoor environment, adding: “it is clear that, as noted by Florence Nightingale, buildings with high ceilings and with large openings are optimal for natural displacement ventilation 2 .” Figure 1. Air pathway of exhaled breath within an unventilated office when using screens and masks. Driven by personal heat plume, equipment, radiators, colder surfaces (Ventive & Brunel University London).

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