key: cord-0919308-yyuigkh3
authors: Kohli, Indermeet; Lyons, Alexis B.; Golding, Bob; Narla, Shanthi; Torres, Angeli E.; Parks‐Miller, Angela; Ozog, David; Lim, Henry W.; Hamzavi, Iltefat H.
title: UVC Germicidal Units: Determination of Dose Received and Parameters to be Considered for N95 Respirator Decontamination and Reuse
date: 2020-08-07
journal: Photochem Photobiol
DOI: 10.1111/php.13322
sha: d057ac6cc09d36e176fac8be17b2a6f3eaccbccc
doc_id: 919308
cord_uid: yyuigkh3

The COVID‐19 pandemic has resulted in an international shortage of personal protective equipment including N95 filtering facepiece respirators (FFRs), resulting in many institutions using ultraviolet germicidal irradiation (UVGI) technology for N95 FFR decontamination. To ensure proper decontamination, it is crucial to determine the dose received by various parts of the FFR in this process. Recently, our group customized a UVGI unit for N95 decontamination. With experimental and theoretical approach, this manuscript discusses the minimum dose received by various parts of the N95 respirator after one complete decontamination cycle with this UVGI unit. The results demonstrate that all parts of the N95 FFR received at least 1 J/cm(2) after one complete decontamination cycle with this unit. As there are a variety of UVGI devices and different types of FFRs, this study provides a model by which UVC dose received by different areas of the FFRs can be accurately assessed to ensure proper decontamination for the safety of healthcare providers.

The COVID-19 pandemic has resulted in a shortage of personal protective equipment (PPE) including N95 filtering facepiece respirators (FFRs). As such, decontamination methods, such as ultraviolet germicidal irradiation (UVGI), are being utilized for their re-use. The decontamination efficacy of UVGI has been well documented in the literature with a greater than 3 log reduction achieved after UVGI treatment with various doses. (1) (2) (3) (4) Possible explanations for the variations in UVGI dosing may include 1) differences in the pathogens as each would need a dose based on the specific biologic formation, 2) the variation between substrates used which may be porous or non-porous, flat, or curved, and 3) the distance from and uniformity of the UVGI radiation source. (5) (6) (7) With multiple institutions repurposing their UVGI technology for N95 decontamination, hospital systems across the United States have started utilizing UVGI for FFR decontamination and reuse. Dosing is a crucial parameter, and insufficient doses would result in incomplete decontamination which can be hazardous to the healthcare worker. A dose of at least 1 J/cm 2 has been recommend for N95 decontamination. (8) (9) (10) (11) Considering that the UVC photons are only effective if they make direct contact with the surface, and that N95 respirators have a curvature, it is important to account for the actual dose received by various parts of the respirator within the repurposed unit. Recently, our group customized a UVGI unit for N95 decontamination and reuse, referred to as Daavlin unit in this manuscript. (4) With an experimental and theoretical approach, this manuscript discusses the minimum dose received by various parts of the N95 respirator after one complete decontamination cycle with this UVGI unit.

This method, to determine the dose received by various parts of the N95 respirator, can be utilized as a model for other UVC units repurposed for N95 decontamination. In addition, parameters that healthcare institutions across the country might consider when investing and utilizing a UVGI unit for the purpose of N95 decontamination have also been suggested.

Daavlin desktop UVC germicidal lamp (Daavlin, Byron, OH, USA), referred to as Daavlin unit in the manuscript, was utilized for UVGI irradiation.(4) A 3M 1860 N95 FFR was utilized as a model FFR.

This article is protected by copyright. All rights reserved To measure the variation in the dose received by various parts of the N95 FFR, two different factors were considered-the impact of the curvature of the N95, and the distance of the irradiated site from the lamp. To account for the effect of the FFR curvature, irradiance was measured at various angles between the surface normal and incident UVC. Figure 1a is a schematic of the orientations of surface normal on a representative N95 respirator. Measurements were made by orienting a UVC sensor at angles ranging from 0-90 o between surface normal of the sensor and incident UVC (Fig. 1b) . A calibrated UVC meter UV512C (General Tools and Instrument, Secaucus, NJ, USA) was utilized.

The sensor was placed on the stainless-steel mayo stand tray, readily available in clinical settings, when making measurements. Of note, the tray/table was approximately 14 cm from the lamp, and the sensor was about 11.5 cm (height of sensor 2.5 cm) (Fig. 1 b) .

To estimate the effect of distance on irradiance, a simplistic approach was to consider that a radiation source, including a UVC lamp, is a point source that irradiates uniformly in all directions. In this case, irradiance at a distance r from the source follows the inverse square law and is proportional to 1/r 2 , where r is the distance from the lamp.(12) However, this approximation is valid only when irradiance is measured at distances greater than five times the longest dimension of the source. The longest dimension of the lamp used in the Daavlin unit was approximately 38.5 cm, and the tray containing the N95 FFRs was placed at a distance of approximately 14 cm from it. Since this distance is much smaller than five times of the longest dimension of the lamp (5*38.5 = 192.5 cm), it made the point source approximation invalid in this situation. To make a conservative approximation of the variation in intensity with distance from the lamp, with detector directly facing the lamp, line source model(13) described by the Eq. 1 was utilized instead.

Here, E is the irradiance, is the intensity per unit length, ɸ is the useful UVC intensity (at 254 nm), L is the length of the lamp, h is the distance from the end of the lamp (for a point located at the midpoint of the lamp h=L/2), and d is distance between lamp and irradiated site. ɸ was approximated to be 12 W which is about one third of the wattage of the UVC lamp (36 W), L was 38.5 cm (the length of the UVC lamp), h was used as L/2, and d was varied to account for change in (Eq. 1)

This article is protected by copyright. All rights reserved irradiance with distance from the lamp. Equation 1 was utilized to calculate the irradiance factor. This factor, in combination with the measured irradiance values with the UVC meter, provided the irradiance variation as a function of distance from the lamp. Equation 1 is applicable to all systems with set up similar to the one discussed in this manuscript, namely, Daavlin unit with tubular lamps.

As discussed above, the irradiance estimation approach (approximately 1/r vs 1/r 2 ) is impacted by the device geometry, type of lamp, distance between the lamp and N95, etc, and should be selected accordingly.

Additional experiments were also performed with UV strips. >Figure 2<

To measure the variation in the dose received by various parts of the N95 FFRs, two different factors were considered-the first being the impact of the curvature of the N95 and the second being the distance of the irradiated site from the lamp. For the Daavlin unit, the effect of the FFR curvature was accounted by measuring the irradiance at various angles between the surface normal ( Fig. 1a) and

incident UVC. With the sensor facing the incident UVC radiation (orientation a in Fig. 1b) , an

irradiance of approximately 10 mW/cm 2 with less than 10% variation was measured at various sites Accepted Article within the irradiation area. However, as expected, with changes in sensor orientation, a reduction in irradiance by less than a factor of 2 was observed between the two extreme orientations from 10.2 mW/cm 2 (at orientation a in Fig. 1b ) to 6.2 mW/cm 2 (at orientation g in Fig. 1b) . Considering that the N95 respirator has a small curvature, it can be approximated that the lowest irradiance received at the curved surface corresponds to the sensor orientation f in Fig. 1b . Towards the edge of the unit, the measured irradiance for this orientation was 4.0 mW/cm 2 . In order to minimize the effect of irradiance variation near the edges of the unit, for the Daavlin unit, it is suggested that the placement of the respirators be such that there is at least a 10 cm distance between the edge of the N95 respirator and the unit edge on the controller side and approximately 5 cm on the other side. This recommendation is based on the lamp positioning within the unit. This will ensure that the lowest irradiance is at least 6 mW/cm 2 . As such, curved parts of the N95 respirator closer to the tray will observe 60% of the dose administered referred to as curvature factor in Table 1 .

Following the effect of curvature, the effect of distance of the irradiated site from the lamp was investigated. For the Daavlin unit, when a dose of 1.5 J/cm 2 was entered into the control panel, the time was automatically accounted for by the UV sensor integrated into the unit. The sensor, located at the top of the unit above the lamp, was calibrated to use irradiance at a distance of 14 cm from the UVC lamp which corresponded to the distance between the lamp and the table/tray surface (Fig. 1b) .

Areas closer to the lamp should observe a higher irradiance resulting in a higher dose received.

Irradiance factor, shown in Fig. 1c , was calculated from Eq. 1 by normalizing against irradiance at a distance of 14 cm from the lamp. Irradiance values at various distances from the lamp were determined by utilizing the irradiance factor and the measured irradiance values of approximately 8 mW/cm 2 at a distance of 14 cm from the lamp and approximately 10 mW/cm 2 at a distance of 11.5 cm from the lamp. The height of the N95 FFR varies with the model, and a conservative approximation is about 6 cm. Considering this, the closest part of the respirator, when treating either surface, will be approximately 8 cm from the lamp and will observe 1.99 times the irradiance observed at a distance of 14 cm from the lamp (Fig. 1c, Table 1 ).

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Considering the impact of both curvature and distance from the lamp, the dose received by various parts of the N95 during UVC treatment of one surface with 1.5 J/cm 2 was found to range from approximately 900-2900 mJ/cm 2 (Fig. 3 , Table 1 ). The received dose was calculated using Eq. 2.

Received Dose (J/cm 2 )=Administered dose (J/cm 2 ) *Curvature Factor* Irradiance Factor

Here, for the Daavlin unit, the administered dose when irradiating one surface was 1.5 J/cm 2 . Of note, presence of UVC lamps on either side will increase the observed dose. In addition, utilization of a highly reflective surface, such as polished aluminum, as a base/tray (and on interior sides and back) with the Daavlin unit will further increase the uniformity as well as overall UVC irradiance within the unit resulting in a higher received dose.

Due to the shortage of PPE across the US, various institutions have repurposed their UVGI technologies for N95 decontamination. Since N95 respirators have curved surfaces and all the UVGI devices have unique geometries, methodology described in this manuscript should be utilized to collect irradiance data for variation due to angle and distance from UVC lamp. This data will help determine the dose received (eq. 2) by various parts of the N95 decontaminated by utilizing the corresponding UVC unit. In addition, irradiance measurement, as a function of angle, performed near the edge of the unit will provide important instructions regarding placement of N95 respirators during a decontamination cycle to ensure appropriate dosing is received. 

This article is protected by copyright. All rights reserved Important factors to be considered when determining and comparing efficacy of potential UVGI devices, specifically for N95 decontamination, include maximum irradiance of the UVC unit, if the irradiance was measured or calculated, availability of fit testing data after UVC treatment, number of decontamination cycles after which the FFR would pass fit-testing, the maximum number of respirators that can be treated during 1 cycle, cost, and whether or not the device requires a ventilated room. To facilitate these considerations, these parameters are included in Table 2 with suggested scoring which can be used to gather device-specific information by institutions to compare UVGI devices. This scoring system was developed to serve as a screening tool when our hospital system was approached by multiple vendors with the repurposed UVC technologies for N95 decontamination.

Although not validated, it proved to be practical and useful. Other institutions may benefit from this as well.

>Table 2<

In conclusion, this study presents a model for careful and methodical assessment of the efficacy of UVC in decontamination of N95 respirators. While a specific UVC device and one type of N95 respirator were used, the assessment process can be generalized to other UVGI devices and other types of respirators. It is imperative that this type of assessment be performed to make sure that the decontamination process is properly done. Failure to do so could result in catastrophic consequences for the front-line healthcare workers.

The Authors would like to acknowledge Akbar Hussaini, Singa

Tobing, Steve Gail from BASF and Devais Parejo from Hoenle UV Scan for their technical assistance and support. 

This article is protected by copyright. All rights reserved 

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mitigate-shortage-respiratory-protection-devices-during-public-health-emergencies. 10. N95DECON. Technical Report for UV-C-Based N95 Resude Risk Management