Study: UV-C Light is Effective for Killing COVID-19 on N95 Masks

October 5, 2020
Jill Murphy, Assistant Editor

Researchers found that N95 facemasks could be decontaminated using a prototype phototherapy unit that dispenses a UV-C dosing level high enough to effectively kill the virus is less than 2 minutes.

Dermatology researchers have found that certain N95 respirators tainted with coronavirus disease 2019 (COVID-19) can be effectively and safely decontaminated for reuse using ultraviolet-C light, a method commonly used for treating skin diseases.

Researchers at Henry Ford Health System found that the outside and inside of the N95 facemasks could be decontaminated using a prototype phototherapy unit that dispenses a UV-C dosing level high enough to effectively kill the virus is less than 2 minutes while still preserving the facemask’s breathability, fit, and overall integrity.

The decontamination process worked best on 2 models: facepieces on 3M 1860 and Moldex 1511 and straps on 3M 8210 and Moldex 1511. The effects of the dosage varied on the other tested models and their straps, suggesting that the UV-C radiation can degrade them, according to the study.

Wiping the straps with ethanol before decontamination would likely be required as an additional disinfection step in the process to maximize the wearer’s safety, according to the researchers.

Fit testing is highly recommended by researchers each time a disinfected facemask is returned for use or a new model is being worn for the first time.

“Our findings reveal a practical, and viable option should hospitals encounter shortages of N95s in the future,” said David Ozog, MD, chair of Henry Ford’s Department of Dermatology in Detroit, Michigan, in a press release. “Using UV-C has been shown to be effective in killing other coronaviruses and the flu virus. We were able to replicate that sterilization effectiveness with COVID-19.”

The research team centered on the potential for decontamination of N95s for reuse by health care workers, examining the reliability of the prototype unit and ultraviolet light, the minimum dosage needed for decontamination, the importance of fit testing post-decontamination, and 4 common methods associated with facemask decontamination.

UV-C is 1 of the 4 methods considered for facemask decontamination and is well known for its ability to penetrate the DNA of bacteria and microorganisms and prevent them from multiplying or replicating. Previous research has shown UV-C to be effective at killing the flu virus as well as 2 other well-known coronaviruses: severe acute respiratory syndrome and Middle East respiratory syndrome.

For the study, 5 types of N95s were tested, with the respirators contaminated with 4 drops of the COVID-19 virus taken from viral stocks obtained from the federal government’s Biodefense and Emergency Infections Research Resources Repository. The virus droplets were placed in the nosepiece, apex, chin, and strap.

The facemasks were kept dry in a biosafety cabinet at room temperature for 40 minutes, before being moved to the phototherapy unit for decontamination using a dose of 1.5 J/cm2 UV light radiation to each side of the mask for approximately 60 seconds. The effectiveness of decontamination was measured in analytical chemistry terms by limit of detection (LOD) and no cytopathic effect (CPE). LOD is the minimum of concentration of a component that can be reliably detected, whereas the CPE means the virus yielded no infectious properties.

The researchers found that all 5 facepieces had below LOD and no CPE, but some had traces of the virus on their straps. In addition, they cautioned that none of the N95s tested were visibly soiled.

Not all of the N95s are created equally and may not withstand contamination, with degrading possibly occurring in the facemask’s outer surface and the elasticity of the bands, according to the researchers.

“Given the current COVID-19 pandemic, extreme measures are needed to keep those on the front line protected,” said Angela Torres, MD, a Henry Ford dermatology fellow, in a press release. “These options are cost effective, quick to employ and have the potential to save many lives and valuable resources.”

REFERENCE

Henry Ford study: UV-C light is effective for killing COVID-19 on N95s. Henry Ford Health System. https://www.henryford.com/news/2020/09/n95-mask-decontamination#:~:text=DETROIT%20%E2%80%93%20Dermatology%20researchers%20at%20Henry,method%20commonly%20utilized%20for%20treating. Published September 22, 2020. Accessed September 29, 2020.