Researchers Develop a Faster, Better Way to Disinfect N95 Masks for Reuse

A team of University of Chicago researchers has developed a better way to decontaminate N95 masks – potentially saving the academic health system thousands of the sought-after masks during the COVID-19 pandemic.

Ultraviolet C (UV-C) – a wavelength of light with the ability to kill germs – has emerged as the preferred solution for disinfecting personal protective equipment (PPE), because of ease of deployment and widespread applicability. Still, it is not without its drawbacks, because, as with any light, UV-C systems can cast shadows, leaving certain surfaces in the dark.

To address this issue, Peter J. Eng, PhD, an experimental physicist and research professor at UChicago, designed and fabricated an N95 respirator decontamination cabinet, which features a proprietary UV-C lamp arrangement that eliminates shadowing and optimizes the UV-C dose to all surfaces of the mask. The result is full irradiation and disinfection of mask surfaces at a rate of 180 masks per hour – though the inventors estimate a scaled-up, automated version could process up to 1,440 masks per hour, or more than 34,000 per day.

The idea came to Eng – who uses an ultraviolet curing system in his lab at the Center for Advanced Radiation Sources – during the first days of Chicago’s shelter in place order, which was issued in mid-March. Unable to sleep one night, he got out of bed and began researching different decontamination techniques. By morning, he had discovered a large body of published work that indicated UV-C irradiation was effective in rendering viruses inactive and began placing calls to various researchers. Based on this information, he made a few preliminary calculations and produced a 3D Solidworks model and a list of components for a dedicated N95 mask disinfection device.

“Being a scientist working in the research world, specifically in designing equipment that we use for doing experiments, I’m used to contacting authors and companies, so I just started reading papers and developing a database,” said Eng.

The next day his friend and colleague Naoum Issa, MD, PhD, from the department of neurology, directory of epilepsy research, clinical quality improvement committee, put him in contact with Jon Brickman, MS, CRCST, the executive director of perioperative and procedural service also at the University of Chicago Medicine. Brickman, whose job includes preserving PPE, helped Eng define the requirements for a system that would meet the needs of the medical center. Issa also provided his clinical input on methods and needs for disinfection protocols.

“In talking with Jon, I discovered that he had an urgent need to start a disinfection process using existing high-powered UV disinfection units that the hospital already owned,” Eng added. Putting his initial idea for the decontamination cabinet aside, Eng began looking into the details of these units and a way to temporarily repurpose the hospital’s equipment to disinfect an array of masks, instead of the operating and patient care rooms for which the units were designed.

“Senior leadership recognized early on that a national shortage of N95 respirators would require us to act swiftly to preserve and extend our inventory. Based on the literature at the time and access to readily available commercial UV disinfection units made ultraviolet germicidal irradiation an attractive option for our facility,” said Brickman, who described Eng as the catalyst for moving from “we can do this with the units we have” to “we can do this better.”

With copper piping and a blow torch in hand, Eng spent the weekend working with his friend, artist, and carpenter, Steve Badgett, soldering a frame structure to hold the masks. A few days later, Eng and Badgett delivered five rolling frames to Brickman together with a detailed room map that marked out the placement of the lamp towers around the N95 mask frame.

The full room system layout shows masks mounted to movable frames that are illuminated by three UV-C emitter towers. Each frame holds 32 masks and the wearer’s name tag, and can be moved to various workspaces. (Image courtesy of Peter Eng)

Eng and Brickman then set up a laptop connected to a UV sensor and built a data logging system to refine the process and provide documentation. “Working remotely with [Brickman] in the hospital, we collected a very rich data set validating the process using a UV-C sensor placed at all different locations and angles, simulating various surfaces of the mask,” said Eng.

UChicago Medicine has been using the system to disinfect masks since the beginning of April. Over the course of the pandemic, reprocessing could save the academic health system thousands of the hard-to-come-by masks.

The Decontamination Cabinet

Once the hospital system was up and running, Eng turned his focus to developing the cabinet system and brought in a team, including Patrick La Riviere, PhD, from the department of radiology, committee on medical physics, and Riviere’s graduate student, Talon Chandler, who provided computational modeling of UV illumination of the 3D masks to prevent shadowing. Benjamin Stillwell, MS, a research engineer manager at the Fermi Institute, and Michael Proskey, a research engineer in Eng’s group, also helped design and fabricate the prototype.

A week after assembling a team, the prototype was built, tested, and could disinfect masks.

Prototype of the small-scale, self-contained disinfection unit. (Image courtesy of Peter Eng)

“Key here is that by optimizing the light array inside the box you evenly illuminate all the surfaces and minimize the amount of time it has to be in there,” said Eng – noting that it also is vital that any one surface of the mask isn’t subject to much more light than any other. This is important because reuse is predicated on the total dose of radiation a mask receives. “It’s not simply the number of times it goes through the system, it’s the sum total of irradiation. By homogenizing that pattern, it maximizes the number of disinfection cycles,” explained Eng.

The hospital this week will begin using the cabinet system to disinfect more masks. A second version also is in the works, and Eng is actively engaging with product design companies to evaluate the design and complete any necessary changes in order to produce a set of drawings that could be used by a manufacturer. In the future, Eng suggests the system could benefit other industries as well, such as manufacturing.

“To me, it’s a process that I can easily imagine in a factory,” said Eng, who used to work on a packaging line at a food supply company. Still, backed with published articles and measurements of the actual system, he said the numbers speak for themselves: “That makes me feel like I can sleep,” Eng said. “It also lets people make their own decisions – I’m not giving you advice, I’m giving you the source of information.”