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Pharmaceutical & medical


Lowering COVID risk with smart ventilation


Here, Vaisala’s Anu Katka examines the role that ventilation systems will play in protecting people in offices and other work spaces from future microbiological threats. She also explains why the reliable measurement of carbon dioxide will be critically important because it is the best measure of effective ventilation.


return to their offices full time? Or will there be a new preference for more flexible hours and for hybrid working (home + office). Either way, there will be a new, heightened responsibility to account for microbiological hazards such as COVID-19 in the provision of safe indoor environments.


A


LeSSonS from CoVID-19 COVID-19 is caused by the SARS-CoV-2 virus, which is transmitted in two ways by infected people. Firstly, viruses can survive on surfaces for up to several weeks, especially at cooler room temperatures. Consequently, fomite transmission is possible when people touch infected surfaces and transfer the virus to their mouth, nose or eyes. Secondly, the virus can spread from an infected person’s mouth or nose in small liquid particles when they cough, sneeze, speak or breathe. These liquid particles vary from larger respiratory droplets to smaller aerosols of less than 5µm diameter. According to the World Health Organisation


(WHO): Aerosol transmission can occur in specific settings, particularly in indoor, crowded and inadequately ventilated spaces, where infected person(s) spend long periods of time with others, such as restaurants, fitness classes, nightclubs, offices and/or places of worship. Supporting the hypothesis that SARS-CoV-2 is


transmitted primarily by the airborne route, a recent paper in The Lancet provided: Ten scientific reasons in support of airborne transmission of SARS-CoV-2.1 By understanding the modes of transmission, governments have been able to define appropriate


34


s countries emerge from the pandemic, it will be interesting to see what the ‘new normal’ looks like. Will workers


strategies to combat viral transmission with measures such as facemasks, social distancing, hand washing and surface disinfection. Importantly, governments have also recognised the increased threat from indoor environments, with recommendations for outdoor activity and increased ventilation. In November 2020, the UK Government


published a video highlighting the importance of ventilation in reducing the spread of COVID-19. Their report said: “Research shows that being in a room with fresh air can reduce the risk of infection from particles by over 70 per cent.”2 In January 2021 hundreds of Canadian experts


(physicians, scientists, occupational health and safety experts, engineers and nursing professionals) wrote an open letter3


to their Prime


Minister urging him to: “to update provincial COVID-19 guidelines, workplace regulations and public communication to reflect the science — COVID-19 spreads through inhaled aerosols.” One of the key recommendations in the letter was to: “Recommend and deploy carbon dioxide


(CO2) monitors as a surrogate measure in case of inadequate ventilation to reduce long-range transmission risk in shared room air. During a TB


outbreak, CO2 concentrations above 1,000 PPM significantly increased the risk of becoming infected with TB. Improving the building ventilation to a


CO2 concentration of 600 PPM stopped the outbreak in its tracks.”


THe SIgnIfICAnCe of pArTICLe SIze The WHO says that infected people appear to be most infectious just before they develop symptoms. In addition, some infected people are asymptomatic, so it is logical to assume that in an office environment, for example, the main threat


will NOT come from people with severe symptoms such as coughing and sneezing, but from those who do not realise that they have the disease. These people are more likely to exhale viral aerosols of less than 5µm diameter – particles which do not respect social distancing. These fine aerosols are roughly equivalent in size to the particles in cigarette smoke, which, as we know, do not settle readily and are able to spread widely in poorly ventilated spaces. A recent paper published in The Lancet4


described studies of cough aerosols and exhaled breath from patients with various respiratory infections which showed striking similarities in aerosol size distributions, with a predominance of pathogens in small particles (<5 µm). These particles are immediately respirable and can remain airborne indefinitely under most indoor conditions - unless there is removal by air currents or dilution ventilation. Humidity also affects the spread of aerosols because low levels of humidity cause aerosols to become lighter and therefore better able to remain airborne. Humidity has also been shown to affect vulnerability to viral infection because exposure to dry air impairs host defense against influenza infection, reduces tissue repair, and inflicts cell breakdown.


rISK reDuCTIon meASureS Traditional health and safety risk assessments address hazards such as slips and trips, heavy objects, repetitive injury, falling, stress, electric shock, fire and lone working, but to create Covid- secure environments, organisations will need to also include an assessment of microbiological risk. It will therefore be necessary to identify potential sources of pathogenic microorganisms as well as their modes and paths of transmission.


Continued on page 35... June 2021 Instrumentation Monthly


1Greenhalgh. T. et al (2021). Ten scientific reasons in support of airborne transmission of SARS-CoV-2. THE LANCET. https://doi.org/10.1016/S0140-6736(21)00869-2 4Fennelly, K.P., (2020). Particle sizes of infectious aerosols: implications for infection control. THE LANCET, Respiratory Medicine, VOLUME 8, ISSUE 9, P914-924.


2www.gov.uk/government/news/new-film-shows-importance-of-ventilation-to-reduce-spread-of-covid-19#:~:text=Coronavirus%20is%20spread%20through%20the,virus%20transmissions%20happen%20indoors. 3https://ricochet.media/en/3423/there-is-still-time-to-address-aerosol-transmission-of-covid-19


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