In a recent study published in the journal Engineering Reports, researchers evaluated the reduction in exposure to airborne viruses in aircraft cabins when mitigation measures such as mask-wearing and leaving the middle seat vacant were adopted to understand strategies to limit the spread of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) during air travel.
Study: Evaluating vacant middle seats and masks as Coronovirus exposure reduction strategies in aircraft cabins using particle tracer experiments and computational fluid dynamics simulations. Image Credit: FamVeld / Shutterstock
Although aircraft cabins are equipped with advanced high-efficiency particle air (HEPA) filters, the proximity of passengers in air crafts cabins combined with the long duration of flights increases the risk of SARS-CoV-2 exposure and infection during flights.
Various studies have examined the effectiveness of wearing masks and distanced seating in reducing the number of secondary infections in an aircraft during the severe airborne respiratory syndrome (SARS) and hemagglutinin 1 neuraminidase 1 (H1N1) epidemics and the recent coronavirus disease 2019 (COVID-19) pandemic. In addition, the results from many detailed, large-scale studies using different tools, such as aerosol tracer experiments and simulations of computational fluid dynamics, are publicly available, providing an opportunity to analyze data from various sources for a unified perspective.
About the study
The present study used the data from three large-scale studies to analyze two variables, distance from aerosol particle source and particle exposure, using linear regression models.
The United States Transportation Command (TRANSCOM) study provided data on aerosol tracer experiments conducted onboard Boeing 767 and 777 aircraft, which were functional and in use. The National Institute for Occupational Safety and Health (NIOSH) examined the effectiveness of vacant middle seats compared to fully occupied aircraft cabins in reducing droplet exposure by performing MS2 (Emesvirus zinderi) bacteriophage tracer experiments. Boeing also released computational fluid dynamics simulation data on droplet distribution inside a Boeing 737 cabin under varying thermal and ventilation conditions. The results from these three studies were used for the linear regression analysis.
The study was divided into four phases, with the first phase involving a regression analysis of the data from the three studies. In the second phase, the researchers used non-linear regression models built from the data from the three studies to analyze the decrease in aerosol concentration with increasing distance. Phase three involved analyzing the TRANSCOM study data separately for masked and unmasked groups for comparison. Finally, in the last phase, the effects of the mitigation measures were analyzed in the context of factors such as infectivity, source strength, and duration of exposure.
The results reported that leaving the middle seat vacant indicated a 54% average reduction in exposure for individuals in the same seat row as the infected passenger and a 36% average reduction for passengers in a 24-row cabin with one infected individual. In addition, individuals in seats farther away from the infected passenger were at a 41% lower risk of exposure than those sitting adjacent, with a 20% lower risk of exposure. Furthermore, TRANSCOM data analysis revealed a 62% reduction in exposure with universal masking or surgical mask use by all parties, not just the source.
Results from one of phase four notional scenarios, which included 10 infectious individuals, reported prevention of 3.8, 6.2, and 7.6 secondary infections by leaving the middle seat vacant, wearing masks, and following both mitigation measures, respectively. Furthermore, a range of notional scenarios indicated that leaving middle seats vacant reduced aerosol exposure by 37%–38%, while mask-wearing reduced droplet exposure by 57% to 63%. Following both measures was seen to reduce infections by 73% to 76%.
The authors also discussed the importance of properly functioning ventilation systems in reducing exposure to aerosol particles The ventilation rates in aircraft cabins are almost 100 times more than the average respiration rates of humans, resulting in an almost 99% reduction in exposure through efficient particle filtration. However, a reduction in exposure risk does not translate directly to a reduction in infection risk. Therefore, other mitigation measures, such as masking, must be followed to reduce further the risk of infections in confined spaces such as aircraft cabins.
Overall, the study reported that following mitigation measures such as leaving the middle seats in aircraft cabin rows vacant and wearing surgical masks inside the cabin could significantly reduce the exposure to droplets. The exposure reduction also depends on other factors such as efficient ventilation systems, the number of infected passengers in the cabin, infectivity, and exposure distance. However, the results indicated that following a combined prevention strategy of masking and distancing in aircraft cabins reduced aerosol exposure by 73% to 76% across diverse scenarios.
- Bennett, J. S., Mahmoud, S., Dietrich, W., Jones, B., & Hosni, M. (2022). Evaluating vacant middle seats and masks as Coronovirus exposure reduction strategies in aircraft cabins using particle tracer experiments and computational fluid dynamics simulations. Engineering Reports. https://doi.org/10.1002/eng2.12582, https://onlinelibrary.wiley.com/doi/10.1002/eng2.12582