Many buildings are not even achieving current ventilation standards, says Professor Cath Noakes – Ken Kitti-Shutterstock
Ventilating buildings has never been more crucial or high-profile, but the building engineering industry needs much more scientific data to help it improve protection from viral infections, says one of the country’s experts on airborne infection.
Professor Cath Noakes, one of the two engineer members the Scientific Advisory Group for Emergencies (SAGE), told a webinar hosted by the Building Engineering Services Association (BESA) that it was not enough to simply increase ventilation rates in buildings to mitigate transmission of the Covid-19 virus.
She told the BESA webinar: “We don’t yet know how much ventilation we need to get this under control; we might never know that and there will always be some risk, but we can aim to reduce the residual risk as much as possible.”
She added: “It is not enough to just say let’s increase ventilation rates. We know it matters and will be critical for health and wellbeing (including mental health) beyond Covid, so we must get this right.
“We can say we have not seen any evidence of high transmission in well-ventilated spaces – so if we are designing and delivering to the standards set in current building standards that will help, but we may need to go beyond that.”
She pointed out that many buildings were not even achieving current standards and many “had no proper ventilation at all”. She also expressed particular concern about naturally ventilated spaces.
Noakes, who is professor of environmental engineering for buildings at the University of Leeds, has been providing advice on airborne transmission to the NHS and the government throughout the pandemic.
She said bespoke solutions would be needed to deal with the wide range of factors in each indoor space and long-term solutions depended on collaboration between engineers, researchers and policymakers.
“This is a very complex issue and it will take years to build up the amount of data needed to make sure we can do this better. However, as a rule of thumb, we should aim for [air change rates of] 10 litres per second (l/s) per person and CO2 concentrations below 800 parts per million.”
She confirmed that studies had shown the risk was higher indoors when ventilation provided less than 3 l/s per person and that household transmission was a particular concern. She also explained that the virus thrived in cool, dry and dark conditions – so controlling relative humidity should also be considered.
BESA’s head of technical Graeme Fox said Noakes’ “advice was consistent with the messages in BESA guidance on ventilation and indoor air quality that was attempting to turn the lessons learned during the pandemic into practical measures for building owners and managers as well as engineers”.
Fox added: “Her presentation exposed the full complexity of this issue, which reinforces the urgent need for simplified, practical guidance… It also confirmed that there are no silver bullets and our industry is at the forefront of efforts to develop properly planned solutions for the long-term health and wellbeing of building occupants.”