In the last blogpost, we featured a study conducted by Stanford University Photonics Research Center to analyze the performance of two different decontamination chamber geometries for mask sterilization.  With the alarming number of COVID-19 cases escalating around the world, finding a solution to meet the growing demand for personal protective equipment (PPE) for hospital staff serving on the frontlines is critical.  With a shortage of PPE worldwide, many medical facilities are forced to decontaminate and re-use their supply of N-95 masks. Optics plays a role specifically as UV-C lighting is used inside of appropriately configured decontamination chambers to provide the necessary sterilization. 

This week, we are pleased to feature a whitepaper* which outlines the practical guidance on how to do this safely, effectively without comprising the performance of N95 masks.  The whitepaper provides evidence-based design principles for 3 different UV-C based decontamination systems for N95 filtering facepiece respirators (FFR’s).  Zemax OpticStudio was used in the study to compare the results of measurements from prototype chambers to properly sterilize masks for re-use. The approaches in the whitepaper were created with consideration for use in resource constraint communities with hospitals in low-and middle-income countries with a goal to build a cost-effective solution that can be implemented rapidly using general available components.

The N95 masks themselves diffusively reflect, scatter, and transmit UV-C illumination and careful consideration had to be given to account for the overall irradiance level inside the cabinets or container, to avoid shadowing of adjacent N95s. Dr. Jeff Wilde, from Stanford University Photonics Research was able to validate that the irradiance distribution on the masks would achieve appropriate levels needed for sterilization using custom-make detector geometries within Zemax OpticStudio. 

After some preliminary studies and experiments three configurations were selected:

The Horizontal Cabinet: A rectangular cabinet in which N95 FFRs are illuminated from above and below:

The Vertical Cabinet: A rectangular cabinet with doors in which the N95 FFRsare placed in a vertical plane and illuminated from front and behind.

The Cylindrical Design: A cylindrical can in which the N95 FFRs are suspended from a frame located on the axis of the cylinder.

“We are already seeing implementations of the construction of these UV-C decontamination chambers in countries in Africa, this is encouraging to see the impact it will have on these communities to fight COVID-19,” said Dr. Wilde.

Read the full paper Construction and validation of UV-C
decontamination cabinets for filtering facepiece respirators which has been accepted for publishing by the Optical Society of America (OSA).

*Authors of the whitepaper are from Harvard Medical School, Stanford University Photonics Research Center, University of Toledo College of Medicine and Life Sciences and University of California School of Medicine