A research group at the University of Tsukuba investigated the risk of virus exposure from exhaled air (jet jet) when passing face-to-face, and found that the number of aerosol particles peaks within 5 seconds after passing face-to-face.
In the infection route of viruses such as the new coronavirus infection, the residence time in the air is short (3 to 5 seconds), and the residence time is longer than the risk of infection through droplets (with a diameter of 5 to 100 μm, it takes several minutes to several seconds). (for several hours if the diameter is less than 5 μm) the risk of airborne infection from aerosol particles is considered to be greater.Furthermore, since the behavior of aerosol particles floating in the air is extremely complex, analysis and evaluation of their dynamics and the risk of virus exposure is an urgent issue.
In this research, a full-scale mannequin with an aerosol particle ejection device connected to its mouth is mounted on an electric cart, and while the mannequin is moved face-to-face, the ejected aerosol particles are visualized and measured by a particle tracking flow velocity measurement system. We investigated the risk of virus exposure during transit.
As a result, the number of aerosol particles peaked within 5 seconds after passing each other at all moving speeds, including walking, jogging, running, and sprinting, and then rapidly decreased.Therefore, when passing face-to-face, measures such as stopping air intake within 5 seconds after passing, ensuring physical distance, and positioning yourself upwind can effectively reduce the risk of virus infection. It was suggested that it could be done.
Furthermore, the peak of the number of aerosol particles tended to decrease as the passing speed increased.These phenomena are thought to be due to the formation of a wake turbulent vortex behind the mannequin after the exhaled air (jet) passes, and the aerosol particles are dispersed.As the passing speed increases, the relative velocity of the jet and the external flow also increases. Therefore, the diffusion of particles is further promoted.
In addition, we conducted a comparative study with and without ventilation, and found that under ventilated conditions, the peak aerosol particle number at walking speed (5 km/h) was approximately 55% or less compared to non-ventilated conditions. It was found that the risk of virus exposure was significantly reduced due to the diffusion effect.
The findings revealed by this study can be applied to the risk of infections mediated by various aerosol particles, such as influenza and rubella viruses.
Paper information:[Scientific Reports] Peak risk of SARS-CoV-2 infection within five seconds of face-to-face encounters: anobservational/retrospective study
