Simulation of light propagation within N95 filtered face respirators during UV decontamination

Abdallatif Satti Abdalrhman, University of Toronto
Authors: Abdallatif Satti Abdalrhman Chengjin Wang Ron Hofmann Lothar Lilge Angelica Manalac Madrigal Weersink Fynn Schwiegelshohn Tanner Young‐Schultz Aldrich Ngan Frank X. Gu Vaughn Betz

The current COVID-19 pandemic has severely stressed supplies of personal protective equipment (PPE), including N95 filtered face respirators (FFRs). In response, healthcare facilities may be forced to extend the use of their N95 FFRs. Among the different methods suggested for the decontamination of N95 FFRs for reuse, ultraviolet light germicidal irradiation (UVGI) is promising and is recommended by the US centers for disease control and prevention. UVGI-based viral deactivation is an easy-to-use solution, and its efficacy on N95 respirators has been confirmed by several studies. While filter efficacy and integrity of N95 FFRs has been the focus of most of the previous studies, there are several knowledge gaps regarding N95 respirator decontamination using UVGI. An important knowledge gap pertains to the understanding of light penetration through the fabric layers within the respirators. Previous studies did not provide a sub-layer resolution of the diffuse fluence within the respirator. The current study presents numerical simulations of UVC light propagation through seven different FFRs to determine their suitability for UV decontamination. UV propagation was modeled using the FullMonte program for two external light illuminations. The optical properties of the dominant three layers were determined using the inverse adding doubling method. The resulting fluence rate volume histograms and the lowest fluence rate recorded in the modeled volume provided feedback on a respirator's suitability for UVGI and the required exposure time for a given light source. The results showed that while UVGI can present an economical approach to extend an FFR's useable lifetime, it requires careful optimization of the illumination setup and selection of appropriate respirators.

Photochromic indicators for quantitative UV-C dose measurements on N95 respirators inform decontamination treatment designs

Alison Su, University of California, Berkeley
Authors: Alison Su, Samantha M. Grist, Alisha Geldert, Anjali Gopal, Amy E. Herr

The COVID-19 pandemic has caused worldwide N95 respirator shortages, highlighting an urgent need for robust N95 decontamination strategies. With applications in water[1], air[2], and surface[2] treatment, ultraviolet-C (UV-C) irradiation has been recognized as a promising approach to decontaminate N95s, with studies demonstrating inactivation of SARS-CoV-2 analogs on most N95 models when sufficient UV-C dose is applied[3 5. However, validation of UV-C decontamination protocols is stymied by the complex morphology of N95s combined with a lack of robust measurement tools for on-N95 UV-C dose characterization. With a smaller footprint than conventional radiometers, qualitative UV-C photochromic indicators (PCIs) offer promise as scalable and affordable UV-C dosimeters for on-N95 dose measurements.

Here, we present new workflows to translate PCI color change into quantitative UV-C dose measurements and assess the accuracy and specificity of two different UV-C PCI models. We verify a near-ideal cosine angular response of these surface-like sensors, critical for accurate on-N95 dose measurements. Using PCIs affixed to N95s within a UV-C chamber, we measure ~20X dose varia.

Developing a BIS Standard for UVGI Devices in INDIA.

Vineet Rohatgi, ISLE - Indian Society of lLghting Engineers
Authors: Vineet K. Rohatgi

Use of UVGI devices has become common in the world and in INDIA, due to Covid19, for which there is as yet no medicine, no cure. However, since the manufacture and its sale is not regulated, often these devices are ill-conceived,improperly designed that they do not provide the promised disinfection, and more importantly can cause harm to the users.

Alarmed at this plethora of dubious quality devices, on ISLE's initiative, BIS has directed ISLE and Elcoma to prepare a BIS Standards Draft for Performance and Safety which once enforced will ensure only Safe and Effective UVGI devices are sold in the market.

Since there are no precedent standards in either USA or Europe for UVGI devices, the task was made more difficult as the energy (mJ/cm2 of UVC) for disinfection for different pathogens is different.

Answers/solutions were required for many issues,some of which are still a work-in-progress.

Inactivation of enveloped viruses under UVC irradiation across different wavelengths

Ben Ma, University of Colorado, Boulder
Authors: Ben Ma, Charles P. Gerba, Yarrow Linden, Patricia M. Gundy, and Karl G. Linden*

UV devices emitting UVC irradiation (200-280 nm) have proven to be effective for virus disinfection, especially for surface and air disinfection, due to their high effectiveness and limited to no material corrosion. Most previous studies of UV-induced inactivation focused on non-enveloped viruses, including adenovirus and MS2 coliphage. Enveloped viruses, however, may respond to UVC irradiation differently due to their unique molecular structure. In this study, UVC action on three enveloped viruses, including human coronavirus (HCoV) 229E, murine hepatitis virus (MHV), and bacteriophage Phi6, was investigated. UV exposure experiments were conducted using in a bench-scale collimated beam apparatus and five UV devices with different emission wavelengths were tested, including a KrCl excimer, a KrCl excimer with a 220 nm bandpass filter, a conventional low pressure mercury lamp, and two UV LED systems with peak emission wavelengths of 265 nm and 280 nm. UV inactivation efficiencies were determined by comparing the viral infectivity before and after various doses of UV exposures and pseudo-first-order inactivation rates were calculated. Our results show that enveloped viruses can be effectively inactivated using UVC devices, among which the KrCl excimer had the best disinfection performance (i.e., highest inactivation rate) for all three enveloped viruses. Compared to HCoV 229E and MHV, bacteriophage Phi6 exhibited a much higher resistance against UVC irradiation from all tested devices. We are currently investigating molecular-level responses of enveloped viruses under UVC irradiation by assessing the nucleic acid and protein damage. This study provides necessary information and guidance for using UVC devices for enveloped virus disinfection, which may help control virus transmission in public spaces during the ongoing COVID-19 pandemic.