Classroom Aerosol Dispersion: Desk Spacing and Divider Impacts

An aerosol dispersion study was conducted using a CO2 tracer gas in a classroom at the United States Military Academy in order to determine the influence of desk spacing, three-sided desk dividers, and release source on the effect of concentrations throughout the classroom. Furthermore, the configurations that minimized concentrations throughout the classroom were used to inform educators about potential designs to minimize the mixing of aerosols from desk to desk for in person classes amid the COVID-19 pandemic using normalized concentrations of CO2 as a means to indicate infectious aerosols. Specifically, three sources were used (2 in the center of the room, and one farthest from the return vent), two classroom configurations were used (spread-out: desks 84 inches apart, and compressed: desks 60 inches apart center to center), and tests with and without three-sided plexiglass dividers. The classroom was arranged with 3 rows of 4 desks facing the front of the classroom with a CO2 monitor placed on top of each of the 12 (the four front monitors were placed about 18 inches higher in order to replicate the breathing zone of a standing instructor) and one at the return vent. In order to ensure that the differences between tests were due to the variables and not a change in the HVAC settings, the concentrations were normalized by the return vent concentration. These values were compared between tests to analyze differences in each desk’s performance, and a variable was created by summing all the normalized concentrations in the room to evaluate the overall performance of the test configuration. The effects of spacing showed an expected result that as spacing decreased, the normalized concentrations increased for tests with the same release source and divider configuration. Because only two spacing configurations were used, no optimal spacing could be found, but the results support recommendations to maintain social distancing in classrooms. The addition of dividers to the classroom significantly reduced the overall normalized concentration in the room in 7 of the 12 tests, and 5 of the 6 compressed tests where the addition of dividers was the only variable. This suggests that dividers can significantly impact the airflow in a classroom and help decrease mixing in most configurations. Furthermore, it shows that if social distancing guidelines cannot be followed, dividers appear to be more impactful where there is less spacing between each desk. Lastly, a comparison was made between a spread-out, no divider configuration to a compressed, divider configuration to see if more students could be safely put into a classroom by moving from the first configuration to the latter. Although these comparisons may have other factors because the desks location throughout the room changed, there was no evidence to support the hypothesis that a compressed, divider classroom would perform better than a spread out, no divider classroom. Another consideration for educators is high-risk instructors, and it was found that dividers decreased the normalized concentrations in 9 of the 12 tests (and the other 3 were near zero) at the four desks in the front row of the room, where an instructor would stand. This suggests that if the instructor is of the greatest concern, dividers will help prevent mixing from student locations to instructor locations. While these results show general trends that could be applied to other classrooms, it should be noted that not all classrooms will have the same airflow (HVAC conditions and symmetry), and further studies in other configurations and classrooms will be insightful. Although this study did not quantify any degree of cross-infection or viral loads within the tracer gas, it provides useful information on the impacts of spacing, dividers, and sources on the airflow and relative concentrations throughout a classroom and methods to test airflow and in a classroom.