Air Flow Experiments on a Train Carriage—Towards Understanding the Risk of Airborne Transmission

Abstract

A series of experiments was undertaken on an intercity train carriage aimed at providing a “proof of concept” for three methods in improving our understanding of airflow behaviour and the accompanied dispersion of exhaled droplets. The methods used included the following: measuring CO2 concentrations as a proxy for exhaled breath, measuring the concentrations of different size fractions of aerosol particles released from a nebuliser, and visualising the flow patterns at cross-sections of the carriage by using a fog machine and lasers. Each experiment succeeded in providing practical insights into the risk of airborne transmission. For example, it was shown that the carriage is not well mixed over its length, however, it is likely to be well mixed along its height and width. A discussion of the suitability of the fresh air supply rates on UK train carriages is also provided, drawing on the CO2 concentrations measured during these experiments.

Modeling disease transmission in a train carriage using a simple 1D ‐model

“…The ventilation of the Class 802 is similar to other rail stock; therefore, the results described here can be translated to other types of modern long‐distance train carriages. A series of CO 2 experiments were conducted by Woodward et al, 21 which will be used to compare and verify the models in Section 4.…”

“…The 1D‐model requires estimates for the longitudinal flowrate and the turbulent diffusion coefficient, which are not necessarily known a priori. To estimate these parameters, we will compare the 1D‐model with CO 2 measurements conducted in a train carriage by Woodward et al 21 in August 2020. These measurements used passengers as sources of CO 2 .…”

“…In the experiments of Woodward et al, 21 a total of six passengers were placed near the middle or end of the carriage. These passengers were seated over three consecutive rows, with a distance of 0.7 m distance between the rows.…”

“…On average, the infection rate increased by 0.15% per hour of co‐traveling. Woodward et al 21 performed CO 2 and aerosol measurements in a train carriage along with flow visualizations using artificial fog. The flow patterns in the carriage cross‐section were observed to be strongly influenced by the ventilation system and change substantially between the center and end of the carriage.…”

The Control of Metabolic CO2 in Public Transport as a Strategy to Reduce the Transmission of Respiratory Infectious Diseases

“…Many countries are making high economic investments to equip schools with CO 2 meters [ 41 , 42 ]. In addition, other isolated initiatives have successfully implemented this methodology in shopping centers [ 43 ], collective transport [ 44 , 45 , 46 ], offices [ 47 ], or university and school classrooms [ 47 , 48 , 49 , 50 , 51 , 52 ]. Specifically, a recent study in Italy reported an 82% reduction in secondary COVID-19 infections in schools where they controlled air renewal from CO 2 measurements [ 53 ].…”