An Efficient Contamination-Reducing Closet for Reusing Protective Clothing

Abstract

A professional closet with highly efficient disinfection for reusing protective clothing is required to reduce supply and demand and protect the environment. A self-developed ultraviolet-C (UVC) light-emitting diode (LED) package that can emit uniform radiance in a certain distance was developed; and a series of disinfection modules with UVC LED packages were installed in a closet for disinfection. A disinfection module can achieve an over 99.9% disinfection rate of H1N1; E. coli; S. aureus; Pseudomonas aeruginosa; and an over 99% disinfection rate of EV71 within a minute. A 1-min disinfection closet was developed to reuse protective clothing. The closet was well-designed; as well as a series of burn-in tests were performed after the assembly of the closet. The optical and thermal properties of the closet were stable within one minute of a working period during the burn-in test. After disinfection; bacterial filtration efficiency (BFE) and viral filtration efficiency (VFE) were examined on the disposable protective clothing. The disposable protective clothing did not show any degradation after being exposed to UVC for sixty minutes; which means the defensive capability of medical protective clothing can be reused sixty times in light of the self-developed disinfection closet. The disinfection closet provides an efficient method for reusing protective clothing.

1. Introduction

Personal protective clothing is critical for healthcare to lower the risks of exposure to hazardous substances, including body fluids, and minimize cross-infections [1,2,3]. However, hundreds of millions of protective clothes are wasted annually and pollute the environment [4,5]. The textile industry is reported to be the second largest polluter of the environment contributing around 20% of global waste [6]. A qualitative analysis of the cost benefits associated with ultraviolet (UV) disinfection reveals significant financial advantages in three primary areas. First, traditional disinfection methods require the ongoing addition of chemical agents, resulting in elevated operational costs. Furthermore, the expenses related to the procurement and transportation of these chemical disinfectants can be substantial. In contrast, UV disinfection predominantly relies on electrical energy and eliminates the need for chemical agents, leading to reduced operating costs. Second, the operation and maintenance of UV disinfection systems are relatively uncomplicated, which contributes to lower maintenance expenses. In comparison, traditional disinfection methods often involve labor-intensive and time-consuming tasks, such as the frequent addition of disinfectants and the monitoring of their concentrations. Additionally, the storage and management of chemical disinfectants incur costs and require stringent safety measures. Lastly, the overall efficiency of UV disinfection systems can lead to long-term savings, as they can be integrated into existing infrastructure with minimal disruption. This integration not only enhances operational efficiency but also reduces the need for extensive training and additional workforce, further contributing to cost-effectiveness. In summary, the adoption of ultraviolet disinfection presents a compelling case for cost savings and operational efficiency compared to traditional methods.

Reusing protective clothing after disinfection can reduce waste, protect the environment, and reduce public expenditure. Considering the hazard of viruses and bacteria may stitch on the protective clothing after usage, protective clothing should be disinfected before reuse, so protective clothing disinfection methods play an essential role.

Current UVC-based disinfection systems include mobile platforms and fixed installations. Mobile UVC robots offer advantages in full room coverage and autonomous operation but are typically expensive and require rooms to be vacated during operation. Moreover, these systems often struggle with shadow zones, particularly in complex room geometries. Fixed UVC installations, while capable of continuous operation, are limited by their fixed position and may not provide uniform coverage [7,8]. While cold plasma provides chemical-free disinfection at room temperature and can modify surfaces beneficially, it faces limitations in penetration depth and requires complex equipment. Our UVC-based solution achieves similar disinfection goals with simpler operation and better cost-effectiveness, while maintaining excellent material compatibility [9]. Chemical disinfection methods, though well-established and highly effective, present ongoing challenges including chemical residues, environmental concerns, and the need for continuous supply chain management [10]. Traditionally, protective clothing is disinfected once daily by hot steam or chemicals, but traditional disinfection methods may introduce damage to protective clothing [11,12] and increase the risk of infection [13]. Protective clothing must be frequently disinfected several times daily to reduce the risk of infection for medical workers [14]. However, such professional equipment for sterilizing protective clothing frequently and efficiently is rare in the market.

A professional closet with high disinfection efficiency is required. Ultraviolet-C (UVC) is a potential disinfection method to disinfect personal protective clothing effectively. Researchers are sparing effort in improving UVC to inactivate bacteria and viruses from the environment [15,16,17]. The UVC dose and wavelength are critical parameters [18,19,20]. Furthermore, it is reported that the 265 nm UVC has the highest disinfection efficiency according to the germicidal response functions [21]. Current UVC light-emitting diode (LED) technology can fabricate UVC LED chips with a peak wavelength of 265 nm [22]. Another critical parameter related to microbial inactivation dose is the product of irradiance as well as time. The low irradiance of the target surface results in a long disinfection time to achieve the target radiation dose. To reduce the disinfection time, a stacked silicon reflector structure to increase the irradiance of the 265 nm LED chip was demonstrated in the UVC LED package [23]. To achieve uniform irradiance in a specific area, a flipped plano-convex lens to diverge the central rays of a 265 nm LED chip was demonstrated in the UVC LED package [23]. This research presents a significant advancement in UVC disinfection technology through the development of a novel modular UVC LED disinfection system. Unlike conventional mercury-based UVC sources, our innovative approach integrates specially designed UVC LED packages into optimized disinfection modules, enabling precise control of radiation distribution and intensity. The key innovation lies in our proprietary module assembly architecture, which overcomes traditional limitations of LED-based systems by achieving uniform irradiance through strategic spatial arrangement and optical optimization. This modular design was successfully scaled up into a practical disinfection closet that demonstrates unprecedented efficiency—achieving effective sterilization of protective clothing within one minute, a marked improvement over existing systems that typically require 5–10 min of exposure. The rapid disinfection capability, combined with the system’s energy efficiency and mercury-free operation, represents a significant step forward in sustainable PPE reprocessing technology.

2. Materials and Methods

2.1. Implementation and Specifications of a Disinfection Module

A novel type of UVC LED package that can emit UVC with a wavelength of 265 nm was developed [19], as exhibited in Figure 1a,b. High UVC reflective thin film was applied in the UVC LED package to facilitate the irradiance for disinfection. A disinfection module in the closet contained four self-developed LED packages with a working distance of 260 mm, as shown in Figure 1c. A UVC LED disinfection module was designed to sterilize the area of 130 mm × 130 mm at the working distance. The more LED modules are used, the larger area that can be sterilized.

2.2. Working Current Selection

The working current of the UVC LED package should be determined for the disinfection closet. The current affects the junction temperature of the UVC LED, and the junction temperature affects the lifetime of the UVC LED chip. Regarding this particular UVC LED chip (PCC-H35, Photon Wave, Yongin-si, Republic of Korea), it is suggested that the junction temperature should be lower than 90 °C. At 90 °C, the L90 (90% initial radiance) of the UVC LED chip is about 2000 h [24]. Therefore, it is necessary to characterize the junction temperature under different driving currents. In the experiment, a transient thermal tester (T3Ster 2000/100, Mentor Graphics, Wilsonville, OR, USA) was employed to characterize the temperature increase of LED packages from 100 mA to 400 mA, as shown in

Table 1. Relationship of temperature increase with driving current.

Driving current (mA)	100	200	300	400
Junction temperature increase (℃)	14	28	42	55

. It denotes that the temperature increase of the UVC LED package is lower than 60 °C when the driving current is lower than 400 mA. To avoid the temperature overshot, this work selected a 200 mA driving current as the working current of the UVC LED package, and the corresponding temperature increase of the UVC LED package was 28 °C. So the junction temperature was 53 °C considering the room temperature was 25 °C. In some extreme cases, the driving current can be increased to enhance the LED radiance, thus achieving higher disinfection efficiency.

2.3. Irradiance Characterization

The irradiance at 260 mm was characterized by a spectroradiometer (ILT560A Mini-Spectroradiometer, International Light Technologies, Peabody, MA, USA) under different driving currents. The spectroradiometer was placed at a distance of 260 mm from the UVC LED module. If the driving current is 200 mA, the irradiance of 45 μW/cm² can be achieved, as shown in Figure 2.

The homogeneity of irradiance within the working distance should be characterized to ensure the disinfection effect. The irradiance distribution generated by the UVC LED disinfection module was simulated utilizing the Monte-Carlo Ray Tracing method with Tracepro software-7.3.4. The distance between the target protective cloth and the disinfection module was 260 mm. This paper simulated the irradiance distribution at 260 mm, as sketched in Figure 3. According to the optical simulation, it is evident that the irradiance distribution generated by the disinfection module is almost homogeneous.

The irradiance distribution at 260 mm was characterized. The schematic setup is shown in Figure 4. The radiance emitted from the LED package was characterized by measuring the irradiance at the four corners and the center in a 130 mm × 130 mm area of the receiving plate. It can be seen from

Table 2. Results of irradiance distribution.

Position	Irradiance @ 350 mA $(\mathsf{\mu }\mathbf{W}/{\mathbf{c}\mathbf{m}}^2$)	Normalized Irradiance
A	94	92%
B	94	92%
C	92	90%
D	93	91%
E	102	100%

that the normalized irradiance of the center and four corners are all above 90%. The well-designed LED module can distribute homogeneous irradiance on the target disinfection surface.

2.4. Disinfection Efficiency Characterization

To prove the efficiency of the UVC LED disinfection module, Escherichia coli (E. coli) bacteria were employed as a benchmark to evaluate the dosage of UVC to achieve a 99.99% disinfection rate. Following a standard protocol, E. coli bacteria was cultured in standard 4-inch agar plates [25]. Different concentrations of E.coli were prepared, and the whole experiment was carried out in a sterile chamber. The agar plates, after cultivation, were placed under the UVC LED module. The distance between the disinfection module and the agar plate was 260 mm, which is the working distance. 200 mA driving current was loaded on the LED module and lasted for one minute. The irradiation dosage on the target area was 2.7 mJ/cm². The disinfection efficiency is calculated by the eliminated amount of the colony divided by the initial amount via remaining colony counting. The disinfection efficiency could reach 99.99% under the aforementioned working conditions. The results are shown in

Table 3. The disinfection test result of E. coli.

Comparison of Colony Number	Original Colony Number
	$~4.5\times {10}^4$	$~4.5\times {10}^3$	$~450$
Control specimen
UVC-treated specimen

. The E. coli bacteria were inactivated, and it was observed by the naked eye that there were no bacteria in the agar plates.

Other than E. coli, Staphylococcus aureus (S. aureus), Pseudomonas aeruginosa, Klebsiella pneumoniae, Salmonella typhimurium, Legionella pneumonia, Influenza A virus (H1N1) and Human enterovirus 71 (EV71) was tested by SGS HK based on the standard of Technical Standard for Disinfection (2002) [26]. The test species were uniformly distributed on a glass plate with a dimension of 100 mm × 100 mm. The glass plate with specimen was radiated by the disinfection module for 1 min at room temperature with a radiation distance of 260 mm. The UVC-treated specimen and the control specimen were cultured to form a colony. The disinfection test for each species was repeated for three times. The disinfection rate was calculated based on the colony number of the UVC-treated specimen and the colony number of the control specimen.

Table 4. Disinfection test results conducted by SGS HK.

Species	Disinfection Rate (%)	Standard Deviation
Escherichia coli (E. coli)	99.99 (3 trials)	0
Staphylococcus aureus (S. aureus)	99.99 (3 trials)	0
Pseudomonas aeruginosa	99.99 (3 trials)	0
Influenza A virus (H1N1)	99.94, 99.92, 99.9	0.02
Human enterovirus 71 (EV71)	99.83, 99.79, 99.57	0.14
Klebsiella pneumoniae	99 (3 trials)	0
Salmonella typhimurium	99 (3 trials)	0
Legionella pneumonia	99 (3 trials)	0

provides the disinfection rate. Such a disinfection module can inactivate 99.99% E. coli, S. aureus, Pseudomonas aeruginosa, H1N1, over 99.5% EV71, and 99% Salmonella typhimurium, Legionella pneumonia, and Klebsiella pneumonia within a minute (Supplementary Materials File S1).

2.5. Implementation and Specifications of the Disinfection Closet

A disinfection closet equipped with the UVC LED disinfection modules mentioned was implemented for disinfecting the personal protective clothing efficiently. Two sets that each includes seven UVC LED disinfection modules were implemented on the side wall of the closet to sterilize the front-side and back-side of personal protective clothing. Figure 5 exhibited the self-developed disinfection closet. The clothing was placed in the middle of the closet, and UVC radiation can kill the viruses and bacteria on it.

Table 5. Specification of the disinfection closet.

Engineering Parameters
Irradiance wavelength	265 nm
Number of the 265 nm LED package	56
Working current	200 mA
Cloth capacity for one disinfection cycle	1 or 2 protective clothes
Number of the LED module	14
Dimension	550 mm × 530 mm × 1840 mm
Power	60 W
Disinfection time	1 min

shows the specification of the disinfection closet.

3. Results

3.1. Thermal Test

To ensure that the closet temperature was stable and low, a thermal test was conducted. 60 W was set as the input power to ensure the closet would be safe and not be overheated during the disinfection cycle. A thermal camera (FLIR ONE Pro, FLIR Systems, Goleta, GA, USA) was adopted to characterize the temperature of the closet during the test. The thermal image of the closet during the working cycle was shown in Figure 6a, while Figure 6b displayed the closet temperature only raised by 6 °C after 120 min of working time. The working temperature was stable and safe since the working period of the disinfection closet was only 1 min for a single disinfection cycle.

3.2. Irradiance Test

The designed irradiance of the UVC LED disinfection closet is around 160 μW/cm² [27], and it is necessary to ensure that the irradiance at the position of protective clothing is stable at 160 μW/cm². A radiometer (U-20, EVERFINE, Hangzhou, China) was placed in the center of the closet, as indicated in Figure 7a. The closet was turned on for 30 min. The irradiance is shown in Figure 7b, which implies that the irradiance could be stabilized at 160 μW/cm² for 30 min.

3.3. Protective Clothing Filtration Efficiency Characterization

For the purpose of ensuring that the closet would not destroy the protective clothing, a series of standard filtration tests were conducted. Eleven pieces of protective clothing were exposed to UVC for 0–60 min with different exposure time. Bacterial filtration efficiency (BFE) and viral filtration efficiency (VFE) tests were conducted by SGS HK. A small piece with an area of 49 cm² was cut from the eleven pieces of tested protective clothing for VFE and BFE tests. For the VFE test, the standard of in-house modified ASTM F2101-19 [28] was applied. The testing area was 49 cm² with a test virus of phi-X174, and the mean particle size was around 2.7 μm. For the BFE test, the standard of ASTM F2101-19 [29] was applied. The testing area was 49 cm² with a staphylococcus aureus aerosol flow rate of 28.3 L/min. Staphylococcus aureus was employed as the test bacteria, and the mean particle size was around 2.7 μm.

Table 6. VFE and BFE test results.

UVC Disinfection Time (min)	VFE (%)	Standard Deviation of VFE	BFE (%)	Standard Deviation of BFE
0	99.9	0	99.9	0
1	99.9	0	99.9	0
2	99.9	0	99.9	0
3	99.9	0	99.9	0
4	99.9	0	99.9	0
5	99.9	0	99.9	0
10	99.9	0	99.9	0
20	99.9	0	99.9	0
30	99.9	0	99.9	0
60	99.9	0	99.9	0

shows the VFE and BFE test results. All the testing results were 99.9% (Supplementary Materials File S1). The testing results show that the UVC will not destroy the personal protective clothing after 60-min UVC exposure. The personal protective clothing can be reused 60 times with our disinfection closet.

Considering that the disinfection period of a piece of protective clothing is merely one minute, the protective clothing can be sterilized by the disinfection process in the self-developed UVC closet at least sixty times. The self-developed UVC LED disinfection closet provides a method for public institutes to reduce the demand for excessive protective clothing without sacrificing health protection. UVC LED degradation poses a potential risk, as these LEDs can age and experience a gradual decline in irradiance. To address this, a UVC irradiance sensor will be integrated into the disinfection cabinet in the future. This sensor will monitor changes in irradiance and utilize a compensation algorithm to ensure consistent irradiance levels inside the cabinet.

We acknowledge that protective clothing materials vary significantly in composition, thickness, and surface characteristics, which affects UVC disinfection efficacy. To address these challenges, we propose a comprehensive strategy including systematic testing across common PPE materials (non-woven polypropylene, multi-layer surgical gowns, and protective coveralls) and technical adaptations such as adjustable UV intensity and multi-angle irradiation. Our future work will focus on developing material-specific protocols, creating a material property database, and implementing automated material recognition systems. These measures will ensure consistent disinfection efficacy across diverse protective clothing while maintaining practical feasibility in healthcare settings.

While our laboratory results demonstrate promising potential for the UVC LED disinfection system, we acknowledge that successful commercial implementation requires comprehensive real-world validation. Although the prototype achieves effective disinfection of protective clothing within one minute under controlled conditions, actual healthcare environments present diverse operational challenges. Future work will focus on multi-site pilot testing to evaluate long-term reliability, user acceptance, and system performance under varying conditions. Through systematic collection of field data and user feedback, we aim to validate the technology’s practical viability and optimize its implementation in healthcare settings.

4. Limitations

The protective clothing utilized is disposable medical protective gown, known for its high protective efficiency. According to the Chinese standard GB 19082-2009 [30], the filtration efficiency for non-oily particulate matter at critical areas and seams must be no less than 70%. The median diameter of the sodium chloride aerosol particles used for testing is 0.075 μm ± 0.020 μm. Given this high density, it can be inferred that pathogen particles are unlikely to penetrate the material of the protective clothing. Consequently, this disinfection closet does not include a UVC disinfection module for the interior of the protective clothing, which represents a limitation by overlooking the need for internal disinfection.

5. Conclusions

The novel 265 nm UVC LED disinfection modules have demonstrated promising results under laboratory conditions. Our testing revealed key achievements: high irradiance (45 μW/cm²) with uniform distribution at 260 mm distance, stable thermal performance at 28 °C meeting L90 requirements, and rapid disinfection capability (99.99% E. coli inactivation within 1 min). While laboratory tests by SGS HK confirmed 99% effectiveness against multiple pathogens and the system’s ability to preserve protective clothing integrity for at least 60 reuse cycles, we recognize that these controlled environment results require validation in real-world settings. Future studies must focus on extended field testing across diverse healthcare environments, performance evaluation under varying operational conditions, and comparison with alternative disinfection methods. The technology’s practical implementation will benefit from multi-center clinical trials, investigation of effectiveness against emerging pathogens, and assessment of integration within existing hospital workflows. Additionally, long-term durability in high-throughput scenarios and cost-effectiveness across different operational contexts need thorough examination. While our initial results suggest an effective solution for PPE reuse with a 1-min disinfection cycle, successful broader implementation depends on comprehensive field validation and optimization of protocols for various healthcare settings. This technology shows considerable promise, but its practical value must be validated through rigorous real-world testing and comparison with other disinfection methods to ensure optimal safety and effectiveness in healthcare applications.