A Scalable Method for Ultraviolet C Disinfection of Surgical Facemasks Type IIR and Filtering Facepiece Particle Respirators 1 and 2

Due to the SARS-CoV-2 pandemic a shortage of personal protective equipment, including surgical facemasks and Filtering Facepiece Particle Respirators has occurred. SARS-CoV-2 has a 79,5-82% homology to SARS-CoV. The SARS-CoV UVC sensitivity is described in literature. We have performed UVC transmission measurements of surgical facemasks and respirators. In addition, we performed UVC disinfection experiments of S. aureus with surgical facemasks and respirators. Results show that we can achieve an 8-log reduction of S. aureus in the inner layers of FFP1 respirators and the exterior of surgical facemasks. Furthermore, we showed a 7-log reduction of S. aureus in the inner layers of FFP2 respirators. We conclude that UVC disinfection is an effective, safe and scalable method for reuse of surgical facemask and respirators.

and FFP2 respirators. The Dutch National Institute for Public Health and the Environment (RIVM) has approved reuse of FFP2 respirators after hydrogen peroxide and steam sterilization treatment 6 . Surgical masks and FFP1 respirators were not tested. Not every healthcare institution has access to these disinfection facilities. Droplets are mostly filtered at the exterior of the FFP respirators, but aerosols with infectious virus particles are also trapped in the inner layers of the respirators. Because we propose non-personalized reuse of respirators, we think it is important to show that we can thoroughly disinfect the inner layers of FFP respirators by UVC as well. In this paper we substantiate ultraviolet C (UVC) decontamination and reuse of surgical IIR facemasks, FFP1-and FFP2 respirators as a scalable solution to mitigate shortage.

Microbiology
Coronaviruses (CoVs) belong to the order of Nidovirales, the family of Coronaviridae and the subfamily of Coronavirinae. The Coronavirinae subfamily consists of:

alphacoronavirus, betacoronavirus, gammacoronavirus and deltacoronavirus. SARS-
CoV-2 belongs to the betacoronavirus subfamily. SARS-CoV and MERS-CoV also belong to the betacoronavirus subfamily. CoVs are enveloped viruses with a ± 30 Kb large + single stranded RNA genome 7 . The genome of SARS-CoV-2 has a 79,5-82 % homology to SARS-CoV 8,9 . UVC susceptibility studies of SARS-CoV have been described in literature 10 . Therefore, we can infer the UVC susceptibility of SARS-CoV-2. In two studies of respiratory materials of COVID-19 patients the viral load was determined. A total of 27 patients was analyzed. The maximal viral load of oro-and nasopharyngeal samples was 1,5 × 10 7 and 7,11 × 10 8 copies/ml respectively 11,12 . Therefore, we think it is important to achieve an 8-log reduction at the exterior side of the facemask.

UVC interaction
UVC is also used to disinfect water and surfaces 13,14 . The germicidal effect of UVC is the result of a photolytic effect eliminating DNA and RNA replication potential. The absorption spectrum of nucleotides, which make up DNA and RNA, has a characteristic peak at 260 nm, indicating a strong UVC interaction. RNA is known to be more sensitive to UVC than DNA because the Uracil nucleotide that in RNA replaces the DNA Thymine nucleotide has a stronger UVC absorbance. In Figure 1, both absorption spectra are displayed 15 . The vertical line corresponds to a wavelength of 253.7 nm which is the output of a low-pressure UVC source. Singlestranded RNA, e.g. coronaviruses, is more sensitive to UVC than double-stranded RNA and DNA.

Coronaviruses and UVC disinfection
The effectiveness of UVC disinfection on various microorganisms has been well documented in literature and is reported as a microorganism specific D90 dose value expressed in J/m 2 . The D90 dose value is a measure for the UVC tolerance and specifies the dose level at which 90% of a specific type of microorganism is inactivated. The UVC interaction is considered a stochastic effect in which a subsequent D90 dose exposure will subsequently affect 90% of the remainder of the microorganism.

S. aureus serial dilution UVC disinfection experiment
We made factor 10 serial dilutions of S. aureus ATCC 25923 suspension in 0.9% NaCl. We  Aura ™ 1862+ could not be measured by the UVC meter and will be below 0.001 W/m 2 corresponding to an intensity in the middle of the mask lower than 1.5 % from the entrance intensity.    16 . In our experience individual fittest do not lead to rejection of the disinfected masks and respirators. The UVC disinfection procedure can be repeated multiple times. We repeat this procedure up to three times.

Conclusion
We have shown that it is possible to obtain sufficient UVC dose throughout surgical facemasks, type IIR, FFP1 and FFP2 respirators to achieve respectively an 8-log and 7-log S. aureus reduction. The UVC sensitivity of S. aureus is similar to that of SARS-CoV. Due to a high homology of SARS-CoV-2 to SARS-CoV we expect similar disinfection results. Our used UVC dose is not expected to affect respirator material and efficacy. Therefore face-fit will not change with repeated UVC treatments. The process of reusing facemask and respirators should be carefully monitored. Masks and respirators should be collected safely, visually inspected and marked for the number of times they are UVC treated.
The masks and respirator stability under UVC exposure and the widespread application and availability of UVC lamps provide a scalable method for disinfection.