Characterizing the Dynamic Interactions and Exposure Implications of a Particle-Laden Cough Jet with Different Room Airflow Regimes Produced by Low and High Momentum Jets

Abstract

The objective of this study is to examine the dynamic interaction of a cough jet with different indoor airflow distributions created by linear slot diffusers considering the inter-personal transport of coughed particles. The experimental measurements were performed in a chamber, where the interaction of a cough jet and downward jets with various momentums was visualized by smoke. In this study, parameters related to the dynamic interaction of a transient cough jet and a steady downward jet have been studied: (1) distance between the cough jet source and an exposed dummy (ED); (2) the initial momentum of the downward plane jet. The experimental results indicate that the ceiling-attached horizontal jets that are widely applied in the over-head mixing ventilation systems have difficulties in deflecting the cough jet, and thereby have difficulties in reducing inter-personal transport of the coughed particles. This study found that a downward plane jet could prevent the transport of cough particles from the cough dummy to the ED. When the ED is standing 0.5 meter away from the cough dummy, the personal exposure (PE) level to coughed particles by using a downward plane jet could be two orders of magnitude lower than by using ceiling-attached horizontal jets. In addition, this study quantifies the interaction of a cough jet and a downward plane jet in their ability to reduce exposure to coughed particles. The results may be used in the process of diffuser selection and suggests that ventilation systems employing downward plane jets with high discharge velocities might be useful in public spaces to reduce inter-personal exposure to coughed particles.

Airborne transmission between room occupants during short‐term events: Measurement and evaluation

“…In order to evaluate dynamic airborne transmission, a suitable evaluation method is required. In the context of steady‐state conditions, there are two widely used methods for evaluating the risk of cross‐infection, namely intake fraction (IF) and exposure index ( ε s ) …”

“…However, most tracer gas instruments, including the widely used photoacoustic gas monitor INNOVA, have a sampling time of the order of 10‐60 seconds, which is much longer than the period of inhalation or exhalation (which are of the order of 1 second). Aerosol generators have been increasingly used to provide a more accurate simulation of the transfer of exhaled droplet nuclei . However, they are mostly used alone (ie, not in conjunction with a manikin) and have a sampling interval of no smaller than 1 second .…”

“…Aerosol generators have been increasingly used to provide a more accurate simulation of the transfer of exhaled droplet nuclei . However, they are mostly used alone (ie, not in conjunction with a manikin) and have a sampling interval of no smaller than 1 second . CFD techniques are capable of performing high time‐resolution sampling of the concentration.…”

Influence of pulmonary ventilation rate and breathing cycle period on the risk of cross‐infection

“…25 These velocities were in general higher than those measured in human subject studies, where the peak flow velocity during normal breathing was reported to be approximately 1-2 m/s. In general, the pulmonary ventilation rate and breathing cycle period of "standard persons" were used in past studies [3][4][5][6][7][10][11][12][13][14][15][16][17][18][19][20][21][22]30,31,33 of airborne cross-infection. In previous studies using breathing thermal manikins, a breathing cycle period of 6 seconds was usually assumed for a pulmonary ventilation rate of 6.0 L/min and 4 s for 10.0 L/min; the breathing cycle of 2.5 second inhalation, 2.5 second exhalation, and 1 second pause was most widely used, 11,12,30,31 although many studies used a cycle without a pause between exhalation and inhalation.…”

“…For the data under steady-state conditions, time-averaged mean values were calculated.The risk of cross-infection in steady-state conditions was indicated by the parameter exposure index (ε), which has been widely used in past studies [3][4][5][6]10,12,19,[45][46][47][48][49][50]. The FCM data were corrected for the time required for the N 2 O samples to travel in the sampling tube from the sampling location to the FCM monitors.…”