Modeling-based UV-C decontamination of N95 masks optimized to avoid undertreatment

Abstract

As the Coronavirus 2019 pandemic creates worldwide shortages of personal protective equipment, hospitals have increasingly turned to sterilization and re-use protocols, often without significant data supporting the specific methodologies. When using UV-C irradiation, previously shown to be effective for decontaminating hard surfaces, modeling shows the importance of accounting for the porosity and non-uniform curvature of the N95 masks in decontamination procedures. Data shows a standard incident dose of 1 J/cm^2 delivered to both front and back surfaces is more than 500x higher than the known kill dose. However, modeling indicates this would undertreat 40\% of the mask material due to the curvature, path-length attenuation and scatter. Multidirectional UV-C irradiation employing dose calibrated exposures can adjust for this loss and best decontaminate masks. Such protocols can be rapidly implemented in thousands of hospitals across the world equipped with UV-C irradiation lamps without the need for additional capital equipment purchases.

Ultraviolet-C as a Viable Reprocessing Method for Disposable Masks and Filtering Facepiece Respirators

“…Ultraviolet-C is normally regarded as a low-cost reprocessing method. From the SLR’s final sample, most publications used either adapted biosafety [ 6 , 49 , 50 , 57 , 58 , 59 , 61 , 83 ] or sterilization [ 33 , 56 , 86 ] cabinets; adapted chambers [ 7 , 39 , 43 , 48 , 64 , 66 , 75 , 78 ], rooms [ 51 , 68 , 69 , 85 ] or laminar flow cabinets [ 43 , 71 , 80 , 82 ]; the lamps alone [ 38 , 40 , 46 , 52 , 54 , 63 , 79 , 87 ] or tube racks [ 70 ]. Most of these resources are available in research departments or hospitals; making this method “reasonably (…) inexpensive” [ 7 ] (p. 515) or, at least, “a cost-effective alternative to heat or chemical decontamination” [ 69 ] (pp.…”

“…These numbers depend on the area each mask model has and the irradiated area the system has. Despite these studies, this capability becomes easily observed when researchers use adapted rooms [ 51 , 68 , 69 , 85 ] since they can disinfect multiple SUPPE at once.…”

Principles and practice for SARS-CoV-2 decontamination of N95 masks with UV-C

“…Preprints are snapshots in time of science that sometimes is in rapid flux. Since then, related results were published in several preprints and published works discussed below (36,(65)(66)(67)(68)(69)(70)(71)(72)(73)(74)(75)(76)(77)(78)(79)(80).…”

“…Two studies addressed the light propagation inside a N95 mask. Sears et al modeled the effects of uneven UV-C exposure of masks from two sides due to mask curvature, and they suggest the use of multidirectional UV-C irradiation to improve decontamination (76). Lilge et al determined the optical scattering and absorbance coefficients of several N95 mask materials using diffuse transmission and reflection measurements with an integrating sphere and an array spectrophotometer, and they used these parameters for Monte Carlo modeling the light distribution within the layers of the mask (70).…”