Indoor particle dispersion due to hand dryer in public washroom: an in silico study

Hand dryer in public washroom has been reported likely to be a reservoir of drug-resistant bacteria. When a hand dryer being used, the high-velocity air jet from the dryer outlet can carry aerosol particles to hand surfaces, the user, and indoor space. This in silico study considered the effect of different airflow speed of hand dryers on the dispersion of particles in different diameters with and without the user. The aim of this study was to apply the computational fluid dynamics (CFD) method based on the discrete phase model to investigate the trajectory of indoor particles from the hand dryer in public washroom. The CFD results showed that, when the user was using the hand dryer, 42.3% of the particles were distributed on the wall against the user, and 31.6% were distributed on the user's body, including their hands. When no one was standing in front of the hand dryer, 87.6% of the particles fell on the ground. The blocking of user's hand dispersed the particles to a wide range, particularly for the larger diameter particles which were scattered on the user's body or on the ground. In addition, the dispersion proportion of particles did not vary with the speed of airflow, but the area of particles distribution became larger as the speed increased. Our findings suggest that the contamination of the indoor environment caused by the hand dryer could not be ignored, incorporating filters into hand dryers is essential. Furthermore, our work offers valuable insights for optimizing the design of hand dryers.