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Year : 2020  |  Volume : 25  |  Issue : 2  |  Page : 80-85

A low cost ingenious approach for ultraviolet decontamination of N95 filtering face-piece respirators to deal with dwindling supply during the COVID-19 pandemic

Department of Microbiology, Mahatma Gandhi Institute of Medical Sciences, Sevagram, Maharashtra, India

Date of Submission27-Apr-2020
Date of Acceptance06-Jul-2020
Date of Web Publication15-Dec-2020

Correspondence Address:
Dr. Rahul Narang
Department of Microbiology, Mahatma Gandhi Institute of Medical Sciences, Sevagram, Maharashtra
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/jmgims.jmgims_48_20

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Introduction: COVID-19 pandemic caused by severe acute respiratory syndrome coronavirus-2 is rapidly evolving and hospitals are facing the issue of shortage of personal protective equipment (PPE) due to stringent requirements of PPE use. For reuse of N95 filtering face-piece respirators (N95FFR), we prepared an ingenious cabinet with ultraviolet light C (UV-C) using scarce material available during the lockdown period. Materials and Methods: Since like many other microbiology laboratories in medical colleges, we did not have access to viruses, we could not test our product with them. We thus tested the efficacy of the cabinet to decontaminate material using 0.5 McFarland standard broth of Escherichia coli 25922. The broth was exposed to UV-C inside the cabinet for 15 and 30 minutes in Petri dishes, with and without lids. The broth was subcultured on nutrient agar plates, both pre and post exposure. We also could not test integrity and static charge of the respirators; we relied on CDC data on the same. Results: It was observed that there was at least 4 log reduction (99.99%) in the number of viable E. coli on exposure to UV-C for 15 as well as 30 minutes. The plates with glass lids on did not show any reduction in number of viable bacilli. The reduction in number of E. coli was taken as surrogate marker for the reduction of ssRNA viruses. Conclusions: UV-C inside an ingeniously made cabinet can be used to decontaminate N95 FFR in exceptional circumstances of reduced supply under lockdown conditions of a pandemic.

Keywords: COVID-19, decontamination, N95 filtering face-piece respirators, pandemic, ultraviolet C

How to cite this article:
Patond A, Narang R. A low cost ingenious approach for ultraviolet decontamination of N95 filtering face-piece respirators to deal with dwindling supply during the COVID-19 pandemic. J Mahatma Gandhi Inst Med Sci 2020;25:80-5

How to cite this URL:
Patond A, Narang R. A low cost ingenious approach for ultraviolet decontamination of N95 filtering face-piece respirators to deal with dwindling supply during the COVID-19 pandemic. J Mahatma Gandhi Inst Med Sci [serial online] 2020 [cited 2023 Jan 31];25:80-5. Available from: https://www.jmgims.co.in/text.asp?2020/25/2/80/303420

  Introduction Top

Personal protective equipment (PPE) are essential for protecting health-care providers and patients alike in outbreaks of airborne infectious diseases. Due to stringent requirements of proper PPE protocol during the ongoing pandemic of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) disease COVID-19 many hospitals may run low on these protective devices.[1] As a result, both patients and their health-care providers are at increased risk of contracting and spreading COVID-19.

One such PPE is N95 filtering face-piece respirators (N95FFRs) and various techniques have been tested to decontaminate it for re-use.[1] One such technique is through cycles of decontamination with ultraviolet germicidal irradiation (UVGI)[2],[3],[4],[5],[6] that uses ultraviolet light C (UV-C) within 200–300 nm.[7] The UV-C damages genetic material through cross-linking of thymidine and uracil nucleotides, preventing the replication of microorganisms such as viruses and bacteria.[8] At these wavelengths, the amount of pathogen inactivation is directly proportional to the dose of UV radiation, with dosage being defined as the product of intensity (W/m2) and exposure duration (s).[9],[10] Therefore, UV-C may prove to be simple method of disinfection with minimal damage to the respirator avoiding the use of irritating chemicals.

During COVID-19 pandemic in India, hospitals may also face shortage of PPE including N95 FFR. To avert such situation, we searched the literature for its re-use and observed that people had used UV-C in biosafety cabinets and in commercial cabinets to decontaminate N95 FFR.[1] Since the biosafety cabinets were in use for routine processing in the laboratories and due to lockdown, it was not possible to procure commercial products, we decided to prepare, test and use an ingeniously made cabinet with UV-C installation using materials available in the institute's workshop. To validate its efficacy for decontamination, we measured the effect of UV-C on Escherichia coli liquid culture to see if the UV-C was effectively killing bacteria and presumed that it will have similar effect on RNA virus.

  Materials and Methods Top

A wooden cabinet with measurements of 4' × 2' × 2' was prepared in the engineering section workshop of Mahatma Gandhi Institute of Medical Sciences (MGIMS), Sevagram. It was painted white with oil paint for easy decontamination of the outer surface and inner crevices [Figure 1]. Inside the cabinet, we installed a 3' UV-C (kept in the workshop as a spare for biosafety cabinet) generating fluorescent light in the back at a height of 1.5'. On the top inside, we installed a white fluorescent light. Two switches were installed on the lateral outer side of the cabinet [Figure 2] and the cable length was kept at 20' to provide easy access to electric supply. The UV fluorescent lamp produced 240–260 nm UV-C radiation and provided at least an average intensity of 100 μWcm−2 to the cabinet floor. To open the cabinet, a door was placed with hinges on the front portion [Figure 1].
Figure 1: Front view of cabinet

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Figure 2: Side view of cabinet

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To test the efficacy of the UV-C, we performed an experiment using E. coli ATCC 25922 as we did not have access to various viruses. It was obtained from a solid Mueller-Hinton plate that was used as a control for antibiotic susceptibility testing on the previous day. A 4 ml suspension of 0.5 McFarland standard broth of Escherichia coli 25922 was made in peptone water and was kept in the incubator at 37°C for 4 hours to bring it to log phase. From the peptone water, 1 ml each was transferred to four sterile glass Petri dishes, labeled as 1, 2, 3, and 4. Using a standard loop, we transferred one loopful to four nutrient agar plates labeled as Pre-exposure 1, 2, 3, and 4.

After transfer, the lids of Petri dishes 1 and 2 were put back and dishes were transferred to the UV-C cabinet. Similarly, Petri dishes 3 and 4 were also transferred to the cabinet but without lids.

Petri dishes 1 and 3 were exposed to UV-C for 15 minutes and brought out, while Petri dishes 2 and 4 were exposed to for 30 minutes and then brought out. From each of the dishes, subcultures were made on nutrient agar plates labeled as Post-exposure 1, 2, 3, and 4 using the same inoculation loop as was done pre-exposure. All the eight inoculated plates of nutrient agar were incubated at 37°C for 24 hours.

While opening the cabinet, it was mandatory as per standard operating procedure (SOP) to switch off the UV-C and switch on the white light. Reverse was done when in use.

The integrity and static charge of the respirator could also not be tested in our laboratories, so we relied on data from CDC (https://www.cdc.gov/coronavirus/2019-ncov/hcp/ppe-strategy/decontamination-reuse-respirators.html).

  Results Top

The plates were examined 24 hours after incubation [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]. The pre-exposure plates are shown in [Figure 3], [Figure 4], [Figure 5], [Figure 6]. It was observed that there was at least 4 log reduction (99.99%) on the nutrient agar plates that were inoculated from the open Petri dishes exposed to UV-C for the time duration of 15 minutes as well as 30 minutes [Figure 8] and [Figure 10]. There was no reduction in the plates 1 and 2 that were inoculated from the Petri dishes that were exposed to UV-C with glass lids, irrespective of the duration of exposure [Figure 7] and [Figure 9]. This thus proved that a minimum direct exposure of E. coli in broth for 15 minutes was sufficient to kill the bacteria and reduce it by 4 logs.
Figure 3: Nutrient agar plate with Escherichia coli using standard loop as comparator for growth in Figure 7

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Figure 4: Nutrient agar plate with Escherichia coli using standard loop as comparator for growth in Figure 8

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Figure 5: Nutrient agar plate with Escherichia coli using standard loop as comparator for growth in Figure 9

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Figure 6: Nutrient agar plate with Escherichia coli using standard loop as comparator for growth in Figure 10

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Figure 7: Nutrient agar plated with Escherichia coli using standard loop and exposed to ultraviolet C for 15 min. With Lid

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Figure 8: Nutrient agar plated with Escherichia coli using standard loop and exposed to ultraviolet C for 15 min. Without Lid

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Figure 9: Nutrient agar plated with Escherichia coli using standard loop and expoed to ultraviolet C for 30 min. With Lid

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Figure 10: Nutrient agar plated with Escherichia coli using standard loop and exposed to ultraviolet C for 30 min. Without Lid

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  Discussion Top

We used UV-C fluorescent tube that is used for biosafety cabinets (BSC) and thus all the specifications of the BSC UV fluorescent tubes should hold good for our experiment. The technical specifications of the BSC suggest that approximately 100 μW/cm2 of 254 nm UV-C radiation is received along the floor of the cabinet. At this irradiance of 100 μW/cm2, it takes 15 minutes to reach 90 mJ/cm2 (1 W = 1 J/s) that is sufficient to kill any microorganism. We used E. coli in broth for our experiment. In a previous study, on inactivation of bacteria on surfaces, the UV doses for 90% reduction for E. coli, Serratia marcescens, Staphylococcus haemolyticus, Salmonella typhi, Streptococcus viridans, Staphylococcus albus, Shigella paradysenteriae, and yeast were found to be 1.7–7.4 mJ/cm2 while it was 19 mJ/cm2 for Bacillus subtilis and 22 mJ/cm2 for Penicillium citrinum.[11] In other studies, when UVGI effectiveness was investigated on single-stranded (ss) RNA viruses much higher UV doses were needed for 90% inactivation in suspension (12–24 mJ/cm2) than on a surface (1.32–3.2 mJ/cm2).[2],[12] Since, SARS-CoV-2 is a novel virus, we did not have access to the viral culture and could not study the same. However, it may be studied in future research.

It was possible to estimate the time to sterilization, assuming insignificant decay in intensity, homogeneous UV irradiance across the source, homogeneous radiant flux over the area of the plate, survival of microorganisms between media tested in literature and colonized N95 FFR. However, given the geometry of the N95 FFR, there would be concerns about spatial heterogeneities in this delivery and the issue that respirators in different positions could receive different doses. To overcome this issue, we suggested exposure on both the surfaces of the N95 FFR. In another study, we have used E. coli liquid culture to contaminate surface of N95FFR in three concentrations, transferring 100,000, 10,000, and 1000 bacteria to the surface of respirator. After exposing the respirators to UV-C for 20 minutes on each side, the subcultures were made by dabbing the surface on nutrient agar plates (to know survival of bacteria on the surface) as well as by adding the dissected part of the respirator to peptone water and subculturing on nutrient agar plates (to know the survival of bacteria in inner layers). In both situations, not a single E. coli colony was observed (un-published data).

We used exposure of 15 and 30 minutes in glass Petri dishes with flat surface. In addition, to calculate a scaling factor to account for spatial heterogeneity across the cabinet surface, we increased the estimated time to decontaminate by a factor of 5 additional minutes. In another study, the scaling factor required to estimate the minimum sterilization time for FFR in a BSC was estimated to be 15.4–19.8 minutes per side.[13]

The UV-C dose required to inactivate 90% of ss RNA viruses is estimated 1.32− 3.20mJ/cm2.[2] Similar methods using 254nm UV-C light have been investigated with SARS-CoV.[14] During this ongoing pandemic, a protocol to sterilize N95 respirators using UVGI was developed at the University of Nebraska Medical Center.[15] Specifically, they subjected used N95 to 60 mJ/cm2 of UV-C radiation (254nm) – which exceeded the estimated sterilization dose of 2–5 mJ/cm2 for single-stranded RNA by several-fold.[15]

One issue that was thought about was integrity of the respirators. A previous study found that UV-C treatment of FFRs had no effect on the filter aerosol penetration, filter airflow resistance, or physical appearance of the masks.[16] Additionally, the efficacy of UV-C for achieving complete decontamination of FFRs has previously been validated for influenza virus.[3]

Ideally, for infectious diseases that are airborne or transmitted through respiratory droplets, a new mask or respirator would be used for each individual to minimize the transmission. However, crisis such as the current COVID-19 pandemic can create shortages that necessitate measures to conserve PPE. A previous study has suggested that UV-C results in less physical deformation than bleach, microwave irradiation, and vaporized hydrogen peroxide used for decontamination.[5]

Inspired by the protocol developed by Lowe et al.,[15] a workflow to optimize the utilization of institutional resources was made for MGIMS Sevagram as follows:

  1. Prior to use, respirators should be directly labeled to identify the original owner by both name and department
  2. After use, place in sealed packaging and take to cabinet location near COVID-19 outpatient department (OPD)
  3. Using sterile technique, remove masks from packaging and place on the working surface of cabinet. While opening the cabinet, UV is switched off while white light is switched on
  4. Ensure that there is no overlap of adjacent masks as any unexposed areas will not be sterilized
  5. After transfer, adequately sterilize any external surface that came in contact with the used masks or packaging and destroy the packaging via biological waste in red bin
  6. Close the hood and power on the UV-C for 20 minutes, while switching off white light
  7. After this duration, power off the UV-C, open the cabinet, and carefully flip the masks to expose the opposite side, ensuring no overlap of adjacent masks
  8. Close the hood and power on the UV-C for 20 minutes
  9. Again, adequately sterilize or dispose of any external surface that comes in contact with the masks
  10. Once the full duration has elapsed, power off the UV-C and open the hood
  11. While maintaining sterility of the cabinet, write a number on each respirator indicating the number of times, it was decontaminated and place in sterile and sealed packaging, individually
  12. Remove packages from cabinet and redistribute to original owner.

The above protocol by no means guaranteed complete decontamination. It is always possible that respiratory droplets may penetrate into the inner layers of FFR that contains multiple layers of filtration. The UV-C has a limitation that only 23%–50% of it may penetrate through the FFR material.[6] Similar issue was observed in Petri dishes that were kept with lids inside the cabinet and showed equal growth as pre exposure plates.

The integrity of the respirator and its efficacy to decontaminate various viruses was considered based on literature. In at least six studies, filtration performance was found acceptable for 11 FFR models exposed to various UV-C doses ranging from roughly 0.5–950 J/cm2 and UV-C had minimal effect on fit.[4],[5],[16],[17],[18],[19] Another study tested filtration and fit of 15 FFRs and found no adverse effects to FFR performance.[20] Lindsley et al.[4] reported a reduction of the durability of materials of the FFRs for doses ranging from 120 to 950 J/cm2; however, an approximate inactivation of 99.9% of bacteriophage MS2, a nonenveloped virus, and H1N1 influenza A/PR/8/34 were achieved with much lower doses of approximately 1 J/cm2.[3],[6],[21] Heimbuch and Harnish tested the performance of 1 J/cm2 of UVGI against Influenza A (H1N1), Avian influenza A virus (H5N1), Influenza A (H7N9) A/Anhui/1/2013, Influenza A (H7N9) A/Shanghai/1/2013, MERS-CoV, and SARS-CoV and reported virus inactivation from 99.9% to >99.999%.[20]

The polymers within the respirator may get degraded on exposure to UV-C. The number of decontamination cycles and reuse should be determined by the physical degradation of the respirator material, rather than the loss of filtration capacity.[22] In contrast to the eventual degradation of the respirator material, Lindsley et al.[4] found that the straps retained their structural integrity even at high UV doses. This is crucial for maintaining the tight fit of the mask through repeated decontamination cycles.

This cabinet can be a good solution to disinfect N95 FFRs used in non-COVID areas as well as for some other material, such as, mobile phones, pencils, pens, scissors, stethoscopes, and other smaller items being used in the COVID-19 OPD.

  Conclusions Top

With all its limitations, this study was performed to make and validate an ingenious cabinet to decontaminate N95 FFR with UV-C and this can be considered for N95 FFR reprocessing during times of shortage of PPE supplies.

Financial support and sponsorship


Conflicts of interest

There are no conflicts of interest.

  References Top

Bauchner H, Fontanarosa PB, Livingston EH. Conserving supplies of personal protective equipment: A call for ideas. JAMA 2020;323:1911. doi:10.1001/jama.2020.4770.  Back to cited text no. 1
Tseng CC, Li CS. Inactivation of viruses on surfaces by ultraviolet germicidal irradiation. J Occup Environ Hyg 2007;4:400-5.  Back to cited text no. 2
Mills D, Harnish DA, Lawrence C, Sandoval-Powers M, Heimbuch BK. Ultraviolet germicidal irradiation of influenza-contaminated N95 filtering facepiece respirators. Am J Infect Control 2018;46:e49-55.  Back to cited text no. 3
Lindsley WG, Martin SB Jr., Thewlis RE, Sarkisian K, Nwoko JO, Mead KR, et al. Effects of ultraviolet germicidal irradiation (UVGI) on N95 respirator filtration performance and structural integrity. J Occup Environ Hyg 2015;12:509-17.  Back to cited text no. 4
Viscusi DJ, Bergman MS, Eimer BC, Shaffer RE. Evaluation of five decontamination methods for filtering facepiece respirators. Ann Occup Hyg 2009;53:815-27.  Back to cited text no. 5
Fisher EM, Shaffer RE. A method to determine the available UV-C dose for the decontamination of filtering facepiece respirators. J Appl Microbiol 2011;110:287-95.  Back to cited text no. 6
Meulemans CCE. The basic principles of UV–disinfection of water. Ozone: Science and Engineering. 1987;9:299-313.  Back to cited text no. 7
Kowalski W. Ultraviolet germicidal irradiation handbook: UVGI for air and surface disinfection. Springer Nature Switzerland AG; 2010.  Back to cited text no. 8
Dunn CG, Campbell WL, Fram H, Hutchins A. Biological and photo-chemical effects of high energy, electrostatically produced roentgen rays and cathode rays. J Appl Physics 1948;19:605-16.  Back to cited text no. 9
Sureka CS, Armpilia C. Radiation biology for medical physicists. CRC Press, Boca Raton, Florida, United States; 2017.  Back to cited text no. 10
Sharp DG. The lethal action of short ultraviolet rays on several common pathogenic bacteria. J Bacteriol 1939;37:447-60.  Back to cited text no. 11
Meng QS, Gerba CP. Comparative inactivation of enteric adenoviruses, poliovirus and coliphages by ultraviolet irradiation. Water Res 1996;30:2665-8.  Back to cited text no. 12
Card KJ, Crozier D, Dhawan A, Dinh M, Dolson E, Farrokhian N, et al. UV sterilization of personal protective equipment with idle laboratory biosafety cabinets during the Covid-19 pandemic. medRxiv; 2020.  Back to cited text no. 13
Darnell ME, Subbarao K, Feinstone SM, Taylor DR. Inactivation of the coronavirus that induces severe acute respiratory syndrome, SARS-CoV. J Virol Methods 2004;121:85-91.  Back to cited text no. 14
Lowe JJ, Paladino KD, Farke JD, Boulter K, Cawcutt K, Emodi M, et al. N95 filtering facemask respirator ultraviolet germicidal irridation (UVGI) process for decontamination and reuse. University of Nebraska; 2020.  Back to cited text no. 15
Bergman M S, Viscusi DJ, Heimbuch BK, Wander JD, Sambol AR, Shaffer RE. “Evaluation of multiple (3-cycle) decontamination processing for filtering facepiece respirators.” Journal of Engineered Fibers and Fabrics, (December 2010). doi:10.1177/155892501000500405.  Back to cited text no. 16
Viscusi DJ, King WP, Shaffer RE. Effect of decontamination on the filtration efficiency of two filtering facepiece respirator models. J Int Soc Respir Prot 2007;24:93-107.  Back to cited text no. 17
Bergman MS, Viscusi DJ, Palmiero AJ, Powell JB, Shaffer RE. Impact of three cycles of decontamination treatments on filtering facepiece respirator fit. Journal of the International Society of Respiratory Protection 2011;28:48.  Back to cited text no. 18
Viscusi DJ, Bergman MS, Novak DA, Faulkner KA, Palmiero A, Powell J, et al. Impact of three biological decontamination methods on filtering facepiece respirator fit, odor, comfort, and donning ease. J Occup Environ Hyg 2011;8:426-36.  Back to cited text no. 19
Heimbuch, B.K. and D. Harnish. Research to Mitigate a Shortage of Respiratory Protection Devices During Public Health Emergencies. 2019; Available from: https://www.ara.com/news/ara-research-mitigate-shortage-respiratory-protection-devices-during-public-health-emergenciesexternal icon. [Last accessed on 2020 Mar 25].  Back to cited text no. 20
Heimbuch BK, Wallace WH, Kinney K, Lumley AE, Wu CY, Woo MH, et al. A pandemic influenza preparedness study: Use of energetic methods to decontaminate filtering facepiece respirators contaminated with H1N1 aerosols and droplets. Am J Infect Control 2011;39:e1-9.  Back to cited text no. 21
Lore MB, Heimbuch BK, Brown TL, Wander JD, Hinrichs SH. Effectiveness of three decontamination treatments against influenza virus applied to filtering facepiece respirators. Ann Occup Hyg 2012;56:92-101.  Back to cited text no. 22


  [Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]


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