Probabilità di contagio a grande distanza per via aerea da SARS-CoV-2 nelle scuole italiane
Probability of aerial long-distance infection from SARS-CoV-2 in Italian schools

The problem of the aerial viral transmission from SARS-CoV-2 is of great importance in closed environments, such as school classrooms. A study is presented on three example cases: classroom for primary school, classroom for middle school and classroom for high school. The differences between the three typologies concern the age of the students, their respiratory activity, the air ventilation needs with reference to the 1975 D.M. (Ministerial Decree) on schools: according to this decree it should be guaranteed an air change per our (ACH) equal, respectively, to 2.5, 3.5 and 5 Vol/h. The study was carried out using a variant of the Rudnick and Milton method with the addition of a dynamic discretized calculation to respond to the specific usage profiles for each type of school. Two usage profiles were examined for each type of school: single round of lessons and double round of lessons with intermediate interval, or double lessons with and without intermediate disinfection of the rooms. The results are particularly interesting for all types of schools, especially for the vast majority (estimated 95%) of Italian schools without controlled mechanical ventilation (CMV). The comparison of the probability of individual and global contagion is made for the number of ACH equal to 0.5, 1 and the previewed normal value (2.5, 3.5 or 5 Vol/h) for each school type. The general conclusions are of greater risk, in the case of no mechanical ventilation, The greatest risk arises with the increase in the number of hours spent in the classrooms. We recommend adopting the hour reduced to 30-40 minutes for a total time of 3-4 hours for each round of lessons. Missing hours of lessons can be carried out through Distance Learning (DL). The appendix presents the theoretical development of the modified Rudnick and Milton method with the discretized dynamic analysis with user profile. The theoretical bases of the innovative method are presented with respect to the other known methods.In fact, this method refers directly to the number of people present