The main step for risk criteria assessment was determining the factors affecting the risk of COVID-19 spread based on information from existing studies from both the World Health Organization (WHO) [27] and the Government of Canada website [28]. The number of active virus particles present in a place was considered the most important factor for determining the risk of infection [27]. Various transmission ways of SARS-CoV-2 transmission include airborne transmission caused by small droplets, and larger droplet transmission (droplets can survive up to several days on different surfaces) [54]. The term “viral load” will also be used to refer to the number of active virus particles present in a space. Virus particles live for different lengths of time, depending on a number of factors, the most significant one being surface material. Risk of infection for any particular IndoorGML cell space was modelled as the viral load within the space.