The World Health Organization (WHO) didn’t officially acknowledge Covid-19 airborne transmission risks until May 2021. Yet scientists were seeing growing evidence of those risks almost a year before that and began to focus their research on the importance of clean indoor air, especially in schools, hospitals and offices.
A report commissioned by the UK government’s chief scientific adviser, Sir Patrick Vallance and published in July 2021 by the Royal Academy of Engineering (RAEng) and its partners in the National Engineering Policy Centre (NEPC), focused on the changes needed in public buildings and transport systems to achieve the most effective ventilation and reduce the risk of Covid-19 and other infections.1 Co-author of the report, Professor Catherine Noakes of the School of Engineering at the University of Leeds, commented: “Ventilation is one of the most important measures and can enable a reduction in the risk of infection without restricting our activities.”
The report’s initial findings identified many shortcomings in the design, performance and management of buildings, uncovering what it called, “systematic weaknesses”. Focussing on the most urgent issues, it will be followed by a more detailed review to bring about change.
While this is good news, schools, offices and hospitals need to know that the air inside their buildings is safe right now. Prior to the start of the academic year, UK teaching unions warned that schools urgently needed air filters and carbon dioxide monitors to ensure infection rates and disruptions to children’s learning are kept as low as possible. James Bowen, head of policy at the National Association of Head Teachers (NAHT) said that the pandemic had revealed how many schools don’t have either sufficient space or efficient ventilation and many are in dire need of repairs. He added: “The government’s latest advice on ventilation for schools said open as many windows as you can. If your windows are screwed shut because they’re not deemed to be safe, or you’ve got external doors that are faulty, that’s a real problem.”
Even if windows can be opened, recent research shows that has limited effectiveness compared with HVAC systems or air purifying systems. Much depends on how often and how long windows are open and their position within the room. Researchers from the Massachusetts Institute of Technology (MIT) simulated different types of ventilation in a classroom and concluded: “While open windows may give the impression of ventilation, they also create their own problems as the influx of air near the breathing plane carries contaminants horizontally from an infected person near the window to other occupants.”2
Air filtration experts and the authors of the RAEng report suggest that the key to reducing the spread of Covid-19 indoors involves a whole package of measures including checking ventilation systems are working efficiently, managing the airflow and installing air purifiers and filters as necessary to support natural or mechanical ventilation.
Swedish filtration specialist, Camfil says that installing a ventilation system which supplies the right amount of fresh outdoor air to the room and equipping it with the highest quality air filters is essential to prevent harmful particles entering the building. If buildings need to use recirculated air, it suggests high efficiency filters such as HEPA filters H13 or minimum ePMI 80% filters. If there is an upgrade, it’s important to ensure the fan for the recirculation air in the ventilation system is sufficiently powerful.
Filters and air purifiers
Whether a building’s ventilation is simply open windows or via an HVAC system, air purifiers or filters can complement an efficient system and support an inefficient one, removing harmful particles indoors. Camfil recently installed its City M air purifiers in the classrooms and common areas of the 150-year-old Soho Parish Primary School in central London to protect students and staff. These air purifiers have two HEPA H14 filters with combination media to trap both particles and odour. One side has a HEPA14 (EN1822) filter and the other side is molecular with activated carbon.
German filtration manu-facturer, Mann+Hummel has long experience of producing air filters for clean rooms and operating theatres and was able to react quickly when the virus appeared, installing its antiviral air purifiers in medical practices, gyms and schools.
Jan-Eric Raschke, director of Air Solutions Systems at the company, said: “Antiviral air purifiers are not able to bring fresh air into a room, so it is still necessary to ventilate. The most important thing is that the intervals between ventilation can be significantly extended using the air purifier technology.”