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1. My memo does not adequately capture the sense that the scientific <br />consensus initially ignored the importance of the the aerosol <br />transmission pathway, but that this view is evolving. My belief, and <br />the belief of many other, but not all scientists, is that the <br />preponderance of evidence now supports the idea that aerosol <br />transmission is significant, even by asymptomatic and <br />pre -symptomatic infected individuals2. <br />2. The useful spreadsheet transmission calculator developed by <br />University of Colorado Professor Jimenez should be mentioned: "The <br />Estimator calculates COVID-19 infection risk for a number of basic <br />situations: college classrooms, choirs, taking a bus, being outdoors, <br />participating in demonstrations" .3 <br />Appendix: "Air Exchange Rate" <br />Ventilation system performance is often given in terms of the air exchange <br />per hour (ach)'. Assuming that all the air is well circulated, then the <br />relationship between ach and cfm/person is <br />ach x V/60 x 1/N = cfm/person (1) <br />where V is the volume of the enclosed space in cubic feet, and N is the <br />number of people in the space. ach is also known as the "air exchange rate". <br />I have seen it reported recently that the ach in an aircraft such as the <br />B737 is 20 to 30. Using published figures for the dimension of the aircraft <br />cabin, and ach = 20, then at the designed maximum capacity (189 <br />passengers), I get about 14 cfm/person. To get to 52 cfm/person the B737 <br />capacity should be restricted to about 52 people. <br />A standard subway car for New York City is reported to have about 18 <br />ach'. At its designed capacity of about 188 people, and using published <br />2https://time.com/5883081/covid-19-transmitted-aerosols/ <br />3https: //cires. colorado.edu/news/covid-19-airborne-transmission-tool-available <br />4https: //www.contractingbusiness.com/service/article/20868246/use-the-air-changes- <br />calculation-to-determine-room-cfm <br />5https: //www.nytimes. com/interactive/2020/08/ 10/nyregion/nyc-subway- <br />coronavirus.html?referringSource=articleShare . <br />11 <br />