Abstract
Negative pressure room is indispensable for controlling airborne pathogens such as measles or tuberculosis bacilli. Previously, we proposed layouts to reduce droplet nuclei in the negative pressure room, however, a problem that droplet nuclei in the negative pressure room leaked promptly to a corridor when the door was opened remained unsolved. The push-pull local exhaust has not yet been discussed as a partition of space to prevent leakage. We discussed the conditions of push-pull airflow which prevents air leakage and maintains the air pressure balance even if the door has opened. We modelled installation of a push-pull device in substitution for a door between a corridor and an anteroom. We analyzed the dynamics of droplet nuclei in the corridor and the anteroom using a Computational Fluid Dynamics (CFD) method. We evaluated the effect by counting the number of droplet nuclei in the corridor which leaked from the negative pressure room. The leakage of the droplet nuclei was small if the airflow velocity from the push device was 0.05 to 0.3 m/s, and also low if the airflow velocity to the pull device was more than 0.2 m/s. Larger width of the push-pull device resulted in lower leakage of the droplet nuclei. Wider space between the push device and the pull device also resulted in lower leakage of the droplet nuclei. In the case of the same air volume, doubling the push-pull device width was more efficient than doubling the airflow velocity. The push-pull airflow design is effective as both a local exhaust and as a space partition instead of a door.
