[Numerical study on the impact of mask gap on particle barrier protection]

Objective: The present study investigated the impact of gaps between the mask and human face on particle barrier protection. It revealed the inhalation and deposition patterns of 1-10 μm particles for masks with and without gaps, aiming to provide a theoretical basis for enhancing particle personal protection. Methods: The headand N95 maskmodels were established in August 2023 using three-dimensional modeling technology. The Euler-Lagrange numerical simulation method was employed to simulate inhalation airflow and particle deposition pattern. A MATLAB code was programed to generate randomly distributed particles on the spherical breathing zone, and their trajectories were tracked until deposition on the mask, face, chest, inhalation into the nasal cavity, or escape from the computational domain. Then the inhalation and deposition fractions of micrometer-sized particles were quantified, and the impact of mask gap on particle barrier protection was analyzed. Results: The high-velocity airflow region formed at the leakage site when the mask gap was present. At a nasal inhalation flow rate of 15 L/min, the proportion of inhalation flow through the gap reached 81%. Under sealed mask conditions, 71%-87% of 1-10 μm particles were intercepted within the mask, whereas this retention dropped to 42%-4% in the presence of gap. Without a mask, it was predicted that 93%-52% of particles in the 1-10 μm size range were inhaled through the nose. With a leaky mask, the inhalation fraction decreased to 34%-19%, showing a downward trend with increasing particle size. When the mask was well-fitted and properly sealed, the inhalation fraction dropped to below 1%. Moreover, the surface deposition of 1-10 μm particles on the face and upper chest reached 5%-35% when wearing mask with gap, which was dramatically higher than the 1%-20% under sealed conditions. It was also observed that particle deposition on the human face was concentrated around the eyes. Conclusion: The gaps between the mask and face significantly altered inhalation airflow dynamics, particle trajectories, and deposition pattern, substantially reducing the protective efficacy of masks. To ensure optimal protection in particulate-exposure environments, masks should be worn with a tight seal. Furthermore, facial hygiene is recommended to remove deposited particles and reduce the risk of respiratory injury or infectious disease transmission via inhalation or surface contact.