Phototherapy devices may be repurposed to disinfect N95 masks


By Michael Woodhead

2 Apr 2020

The acute shortage of N95 masks in the COVID-19 pandemic may be alleviated by repurposing UVB phototherapy devices for UVC germicidal disinfection of the respirators, dermatologists in the US say.

Dr ltefat Hamzavi and colleagues at the Henry Ford Hospital in Detroit have worked with phototherapy device maker Daavlin to switch the UV wavelength of the devices’ bulbs to optimise them for coronavirus disinfection.

They say previous studies have shown that UVC radiation have shown that UVC can inactivate respirators contaminated with coronaviruses SARS-CoV and MERS-CoV and H1N1 influenza A.

Working with technicians from Daavlin they have shown that the phototherapy devices produced for use in dermatology practices can be customised to deliver a sufficient dose of UVC radiation to effectively disinfect used N95 respirators so long as they are not visibly soiled.

In a prototype model they developed,  a mask could be disinfected with a irradiance dose of 1 J/cm2 for 1 min 40 sec with the distance from the lamp to the table of 14cm.

Publishing their results in the Journal of the American Academy of Dermatology, they said this dose of UVC would not significantly degrade the integrity of the polymer mask or reduce the efficacy of the respirator and protection to user.

“Considering that many of our healthcare providers are using substitutes for N95 [respirators] that offer very limited degree of protection, using UV germicidal irradiation  and repurposing phototherapy devices could be the best practical solution at this time,” they said.

Speaking to local media, Dr Hamzavi said his group was now developing a protocol and demonstration video to show dermatologists how repurpose phototherapy devices.

However he cautioned that not all masks could stand up to multiple disinfection with UVC irradiation.

“You can irradiate all masks at least once but some masks you can go seven, eight, nine times and still be ok. So you have to clear about which masks you’re using and which light system you’re using to irradiate the masks and clear the virus,” he told WDTN.

“We use phototherapy equipment in our offices all the time to treat skin diseases,” said Dr Hamzavi. “Daavlin was able to repurpose their devices, put in the UVC lamps, then we brought it to Detroit and we tested it against actual masks.”

Other groups have shown that used PPE may be disinfected with UVC using idle laboratory biosafety cabinets.

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