While there are promising earning signs of the approved vaccines’ effects on reducing transmission of COVID-19, it is not yet known how strong those effects are – and for billions around the world, the wait for any vaccine will be arduous. So, while some of the world scrambles to reopen, much of the rest will instead scramble to reduce transmission in the absence of a magic bullet. Now, Bulgaria’s National Centre for Supercomputing Applications (NCSA, distinct from Illinois’ National Center for Supercomputing Applications) is working to improve air filtration systems to make indoor spaces safer for unvaccinated people.

The NCSA is building on work done by RIKEN’s Fugaku system, which stands as the most powerful publicly ranked supercomputer in the world. Fugaku debuted last July nearly a year ahead of schedule to allow COVID researchers to avail themselves of its resources and has, since then, been regularly producing some of the leading simulations of how aerosolized viral particles travel in real-world scenarios: through masks, around face shields, in offices, on trains, and so forth.

Those simulations all bolstered one key takeaway: unventilated, dry, indoor spaces were incredibly dangerous for COVID transmission.

The NCSA honed in on Fugaku’s classroom simulations. The Riken researchers had found that in the simulated classroom, leaving diagonally opposed windows, each open 20cm, would provide fresh air within 500 seconds; opening all the windows and the door in the simulated classroom shortened this time to 100 seconds.

Bulgaria, however, isn’t quite as temperate as Japan, and wintry conditions make opening all the windows and doors a health hazard in itself.

So the NCSA explored reducing infection risks using closed-loop ventilation. Previous work had shown that a safe room of about 20 square meters (three meters high) meant replacing the air twice every hour – if you have just two people. In a classroom of 25+ children, the room could be dangerous within just a few minutes.

The NCSA focused on sterilizing this air with UVC light, which is known to decontaminate aerosols and surfaces. They calculated the necessary installation to achieve 99.9% sterilization of a room’s entire air volume every 25 minutes, creating an environment where, the NCSA claims, “infection is not possible.” The team designed a module with minimal air turbulence, four UVC lamps, and strong ventilation, all in all able to process and sterilize 100 liters of contaminated air per second.

Now, the system is moving ahead to implementation, with the NCSA working with Bulgarian partners (including a Bulgarian UVC lamp manufacturer) to manufacture and install the systems.