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. 2021 Jun 5;6(1):104-115.
doi: 10.20411/pai.v6i1.432. eCollection 2021.

Evaluation of 2 Ultraviolet-C Light Boxes for Decontamination of N95 Respirators

Jennifer L Cadnum  1 , Basya S Pearlmutter  1 , Daniel F Li  1 , Annette L Jencson  1 , Jacob G Scott  2   3 , Ian C Charnas  4 , Curtis J Donskey  3   5
Affiliations

Evaluation of 2 Ultraviolet-C Light Boxes for Decontamination of N95 Respirators

Jennifer L Cadnum et al. Pathog Immun. .

Abstract

Background: Ultraviolet-C (UV-C) light devices are effective in reducing contamination on N95 filtering facepiece respirators. However, limited information is available on whether UV-C devices meet the Food and Drug Administration's (FDA) microbiological requirements for Emergency Use Authorization (EUA) for respirator bioburden reduction.

Methods: We tested the ability of 2 UV-C light boxes to achieve the 3-log10 microorganism reductions required for EUA for reuse by single users. Whole 3M 1860 or Moldex 1513 respirators were inoculated on the exterior facepiece, interior facepiece, and internal fibers with bacteriophage MS2 and/or 4 strains of bacteria and treated with UV-C cycles of 1 or 20 minutes. Colorimetric indicators were used to assess penetration of UV-C through the respirators.

Results: For 1 UV-C box, a 20-minute treatment achieved the required bioburden reduction for Moldex 1513 but not 3M 1860 respirators. For the second UV-C box, a 1-minute treatment achieved the required bioburden reduction in 4 bacterial strains for the Moldex 1513 respirator. Colorimetric indicators demonstrated penetration of UV-C through all layers of the Moldex 1513 respirator but not the 3M 1860 respirator.

Conclusions: Our findings demonstrate that UV-C box technologies can achieve bioburden reductions required by the FDA for EUA for single users but highlight the potential for variable efficacy for different types of respirators.

Keywords: N95 respirator; SARS-CoV-2; bacteriophage MS2; ultraviolet light.

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Conflict of interest statement

C.J.D has received research grants from Clorox, Pfizer, and PDI. J.G.S. and I.C. have received patents for the Synchronous UV Decontamination System (SUDS). All other authors report no conflicts of interest relevant to this article.

Figures

Figure 1.
Figure 1.
Pictures of the ARK 100TM (A) and Synchronous UV Decontamination System (SUDS) (B) devices.
Figure 2.
Figure 2.
Pictures of the 3M 1860 and Moldex 1513 N95 respirators and the sites of inoculation on exterior and interior facepiece surfaces (A) and internal fibers (B and C). For the internal fiber inoculation, the respirators were cut open, inoculated, and sealed. Panel B: 1, exterior facepiece layer; 2, internal layer; 3, interior facepiece layer. Panel C: 1, exterior structural layer (blue); 2, exterior facepiece layer; 3, internal structural layer (blue); 4, interior facepiece layer.
Figure 3.
Figure 3.
Log10 reductions in bacteriophage MS2 (A and B) and 4 vegetative bacteria (C) on N95 respirators after exposure to ultraviolet-C (UV-C) light inside the ARK UV-C box. The test organisms were inoculated on the exterior facepiece, interior facepiece, and internal fibers of Moldex 1513 (A) or 3M 1860 (B and C) respirators. Error bars indicate standard error.
Figure 4.
Figure 4.
Log10 reductions in 4 vegetative bacteria on Moldex 1513 N95 respirators after exposure to ultraviolet-C (UV-C) light inside the SUDS UV-C box. The test organisms were inoculated on the exterior facepiece, interior facepiece, internal fibers, and strap. Error bars indicate standard error.
Figure 5.
Figure 5.
Pictures of ultraviolet-C (UV-C) light colorimetric indicators placed on the interior and exterior facepiece surfaces of Moldex 1513 and 3M 1860 respirators to assess penetration of UV-C from the ARK UV-C box through the full thickness of the respirator material. Yellow, no UV-C exposure; orange, UV-C dose 50 mJ (ie, adequate to kill vegetative bacteria); pink, UV-C dose 100 mJ (adequate to inactivate Clostridioides difficile spores). The color changes demonstrate penetration of UV-C through all layers of the Moldex 1513 but not the 3M 1860 respirator.
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