UV light dosage distribution over irregular respirator surfaces. Methods and implications for safety

Area of Science:

• Environmental Health Engineering
• Microbiology
• Photochemistry

Background:

• The SARS-CoV-2 pandemic caused a global shortage of personal protective equipment (PPE), particularly filtering facepiece respirators (FFRs).
• Ultraviolet germicidal irradiation (UVGI) using ultraviolet-C wavelength is a promising decontamination method for FFRs.
• Adequate dosimetry is crucial for effective UVGI decontamination, ensuring uniform exposure and preventing over- or under-dosing.

Purpose of the Study:

• To investigate UVGI light irradiance variations on different respirator angles.
• To propose and validate a method for simultaneous decontamination of multiple FFRs.
• To ensure appropriate UVGI dosage, especially in shaded areas of the respirators.

Main Methods:

• Construction of a UVGI irradiator with specific dimensions and internal grating for mask placement.
• Assessment of irradiance on two different FFR models (Aura 9322 3M and SAFE 231FFP3NR).
• Utilized an STN-SilverNova spectrometer for wavelength spectrum and surface irradiance verification.
• Performed irradiance pattern simulations using DIALUX EVO 8.2 software.

Main Results:

• UVGI light irradiance significantly varies depending on the respirator's angle, orientation, and shape.
• Irradiance is influenced by the distance from the UV lamps and the angle of light incidence.
• Simulations confirmed that mask geometry and placement critically affect UVGI dosage distribution.

Conclusions:

• A closed-box UVGI system with careful irradiance measurement and simulation can provide reliable and reproducible FFR decontamination.
• The proposed method ensures correct UVGI dosage across all respirator surfaces, balancing overexposure.
• This approach offers a more dependable solution for FFR decontamination compared to open settings.