TRANSDUCERS, TRANSMITTERS & SENSORS


SMART VENTILATION LOWERS RISK


Anu Katka, an indoor environment expert from Vaisala, examines the role that ventilation systems will play in protecting people in workspaces from future microbiological threats


A


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


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. 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 weeks1 room temperatures2


, especially at cooler . 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 Organisation3


(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, 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. 4 Governments have also recognised the


increased threat from indoor environments, with recommendations for outdoor activity and increased ventilation. In November 2020, in a report, the UK Government said: “Research shows that being in a room with fresh air can reduce the risk of infection from particles by over 70%.” In January 2021 hundreds of Canadian experts (physicians, scientists, occupational


30 JUNE 2021 | PROCESS & CONTROL


health and safety experts, engineers and nursing professionals) wrote an open letter6


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 1000 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 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 Lancet7


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 defence against influenza infection, reduces tissue repair, and inflicts cell breakdown.8 To create Covid-secure environments,


organisations will need to 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. Hand sanitiser can be made available and


surfaces can be frequently disinfected. Procedures can be established to reduce the chance of disease transmission, with measures such as screens, social distancing and even disinfectant fogging. However, even with all of these measures in place, one infected person can quickly contaminate large areas. Effective ventilation will therefore be essential, and the control system will need to undertake accurate and timely measurements from each room or space so that it can respond promptly. Some systems may simply monitor CO2 in the exhaust gas,


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