Infrared-based visualization of exhalation flows while wearing protective face masks

Area of Science:

• Fluid dynamics
• Biomedical engineering
• Medical imaging

Background:

• Assessing personal protective equipment (PPE) effectiveness on respiratory flows is crucial.
• Traditional flow visualization methods often require non-human simulators.
• Noninvasive techniques are needed for real-time assessment on individuals.

Purpose of the Study:

• To evaluate infrared thermography as a noninvasive method for visualizing respiratory flows.
• To examine the impact of different face coverings (surgical mask, cloth mask, N95 respirator with exhalation valve) on exhaled airflow thermal signatures.
• To analyze the effectiveness of these masks during various respiratory activities like coughing, talking, and breathing.

Main Methods:

• Utilized mid-wave infrared (IR) thermography for flow visualization.
• Captured thermal signatures of exhaled airflows near the face.
• Quantified thermal inhomogeneities related to carbon dioxide (CO2) concentrations in exhaled breath.
• Observed individuals wearing surgical masks, cloth masks, and N95 respirators with exhalation valves during different respiratory actions.

Main Results:

• Infrared thermography effectively visualized thermal signatures of exhaled air.
• Surgical and cloth masks showed air leakage at edges and fabric, reducing cough jet velocity by approximately four times.
• N95 respirators with exhalation valves significantly reduced IR emission of CO2 near the face, indicating near-complete blockage.

Conclusions:

• Infrared thermography is a safe and effective noninvasive technique for studying respiratory flows and PPE effectiveness.
• Surgical and cloth masks offer partial protection by reducing cough velocity but permit leakage.
• N95 respirators with exhalation valves may lead to increased CO2 rebreathing, warranting further investigation.