Occupational medicine specialist Dr Greg Kew
Indoor ventilation is an important tool to prevent the viral transmission of the Covid-19 virus when correctly applied.
Conversely, poor ventilation promotes viral transmission, Engen industrial hygiene specialist Garth Hunter warned during the South African Institute of Occupational Safety and Health’s safety day webinar, held on September 7.
The webinar is part of this year’s Electra Mining Africa 2020 Connect virtual event, for which Creamer Media's Engineering News & Mining Weekly is a partner.
Hunter pointed out that a Japanese study had shown that Covid-19 spread was 18 times higher in an enclosed environment than in an outdoor environment.
Occupational medicine specialist Dr Greg Kew suggested that ventilation was the “engineering solution” as well as the barrier that one would need to set in place as the foundation of every other measure of prevention, or dilution, of the virus particles.
“The importance of that as a barrier is that it doesn’t depend on behavioural compliance, but one also needs to consider that ventilation is primarily a dilution control, and so, [is particularly effective] for people sitting close to one another, and for those who are breathing heavily,” he explained.
In a factory or office environment, for example, one would need additional layers of control – such as wearing masks and maintaining physical distancing – as the key to reducing the spread of infection.
Further, Hunter explained that a ‘forced’ ventilation system would offer a more guaranteed volume of dilution of the virus, compared with that of a natural system (such as wind-driven ventilation).
However, natural ventilation still remains a viable option should it be the only one available.
Hunter noted that air conditioning systems were not ideal as air was still being recirculated continuously in a space, leading to a build-up of concentrated tiny, virally charged micro-droplets that are expelled into the atmosphere, leading to an increased risk of infection.
Not all barriers are equal, in terms of risk reduction, and as such, he said, “it is very difficult to control Covid-19 through natural ventilation” as it was difficult to measure the levels of carbon dioxide and, therefore, difficult to manage what was happening in the area.
'Forced' ventilation, on the other hand, is designed to supply and remove air to and from a treated space, meaning that the virus concentration is reduced through dilution, leading to a lower risk of infection.
Hunter therefore suggested that companies consider a combination of split unit air conditioning and mechanical ventilation, which supplies outdoor air to each room, and extracts stale air and expels it outside the building.
Through this option, the virus concentration is reduced through dilution with outdoor air.
Alternatively, an all-air heating, ventilation and air-conditioning (HVAC) system could also be considered, but there was a risk of cross contamination through the recirculation of stale air, he noted.
Hunter advised that it was better for all air to be exhausted through a recirculation dumper, which should be set to take 100% outdoor air.