Personal protective equipment (PPE) such as respirators will form the first line of defense in the event of a public health emergency including an airborne pandemic or a bio-terror attack. The two major pathways by which virus-carrying aerosols can reach the human lungs through these PPEs are: a) the intrinsic penetration through porous layers of the PPE and b) the leakage through gaps between the PPE and a person’s face [1, 2]. The contribution from the second pathway can be significantly reduced using fit-testing i.e. by choosing the appropriately sized respirator for a specific face. Unfortunately, in case of an emergency, it would not be possible to fit-test the entire US population. In this scenario, excessive leakage can occur through the gaps. . Hence, it is critical to identify the potential anatomical leak sites (gaps) and quantify the amount of aerosol leakage through surgical respirators for the average US population.
At the behest of Office of Counterterrorism and Emerging Threats, the Center for Devices and Radiological Health, US Food and Drug Administration (FDA), has been developing a comprehensive risk assessment model for determining the risk to different populations in case of an “off-label” use of such PPEs, i.e. for public emergency scenarios for which these FDA cleared respirators were not intended to be used. In order to develop the risk assessment model, establishing a correlation between the respirator gaps and aerosol leakage between the face and the respirator is critical. A previous study  identified the gaps of N95 surgical respirators for a large population and quantified the aerosol leak using computational fluid dynamics. However, the gap surface area, which is a key parameter required for establishing the gap-aerosol leak correlation, has not been quantified before.
In this study, gaps were identified and the gap surface areas were quantified for multiple head-respirator combinations under realistic conditions using imaging coupled with computer-aided design and modeling.