UVC radiation is often used for inactivating the bacteria and viruses in fresh water, air, and surface of objects. During the pandemic, portable UV disinfection devices have emerged in the market, claiming to be able to disinfect personal belongings, or even household environment like door handles and toilet seat covers, etc. The Consumer Council tested 8 models of portable UV disinfection devices available on the market and found that despite having over 97% of bactericidal performance, their virucidal performance vastly varied from about 15% to >99.99%. When using these devices for disinfection, consumers should be aware of the limitations which include whether the object to be disinfected is clean and without dirt, whether its surface is non-porous, is there any overlapping or shadows during application, whether it is placed within the effective line of sight, as well as the intensity, exposure time and distance of UVC, all these will affect the bactericidal and virucidal performance of these devices. With these limitations, portable UV disinfection devices should only be treated as an aid for disinfection. Consumers should not over-rely on their disinfecting efficacy, but always maintain personal and environmental hygiene by employing ordinary disinfecting methods such as wiping object surfaces and crevices with about 75% alcohol-based preparation or diluted bleach solution for more thorough and effective disinfection.
Consumers should pay attention when using UV disinfection devices. Since these devices utilise UVC radiation as disinfectant for surfaces, excessive exposure to UVC will cause harm to eyes or skin. Of the 8 tested models, the photobiological safety of 6 models were rated to be at moderate to high risk. If the UV emitted from these devices accidentally come into contact with human skin or eyes, it may cause discomfort, or even burns or injuries. Prolonged or high dose exposure to UVC can result in photokeratoconjunctivitis, increase risk of cataract, skin erythema, accelerate skin aging and increase risk of skin cancer. As such, consumers should use these products properly, keep a safe distance from the light source and do not stare at it. They should also ensure children or pets stay away from these devices to avoid accidents.
The 8 portable UV disinfection devices tested were priced between $220 and $1,480, including 4 disinfection boxes with wireless charging and 4 other handheld disinfection devices with built-in rechargeable battery. The test covered safety, bactericidal and virucidal performance.
With its shortest wavelength and high energy, UVC disinfects by destroying the structure of bacteria and viruses. The test made reference to the Technical Standard for Disinfection by Ministry of Health, People’s Republic of China, to examine the bactericidal and virucidal performance on object surface of the models in accordance with the operation distance and time stated on their packaging or instruction manuals.
The test result showed that, the average kill rate of Staphylococcus aureus and Klebsiella pneumoniae in half (4) of the models ranged from 97.52% to 99.95%, while the remaining half (4) had an average kill rate of 99.9% or above, among which 1 model if operated with a longer operation time (30mins) could reach an average kill rate of over 99.99%.
However, there is a large variance in virucidal performance among the models. With influenza A H1N1 as the test virus, 1 handheld model performed the worst, with an average virucidal performance of only 14.97%, while 5 other models achieved 72.10% to 98.85% on average. Only 2 handheld models reached over 99.99% in their virucidal performance.
As currently there is no international safety standard applicable to portable UV disinfection devices, the test made reference to the radiation requirements in the International Standard IEC 60335-2-65 for UV devices installed in air purifiers and measured the irradiance of ultraviolet (UV) radiation at 300mm perimeter of each model. According to the standard, irradiance of UV radiation with wavelength of 200nm to 280nm for products should not exceed 0.003W/m2. No UV radiation was detected when the lids of the 4 disinfection box models were closed. However, the UV light of 1 model did not shut off when its lid was fully opened, and its measured irradiance of UV radiation exceeding the upper limit of the standard. 4 handheld models and another disinfection box model with handheld mode were detected with 0.007W/m2 to 1.102W/m2 of irradiance of UV radiation during operation, exceeding the upper limit of the standard. Human expose to the UVC emitted from these models, even for just a short period of time, may injure the skin and eyes.
With reference to the International Standard IEC 62471, the test also measured the effective irradiance at a distance of 200mm from the models, so as to assess the hazard level of UV to skin and eyes. The test result revealed that 4 models, including 3 handheld and 1 box models, were rated at high risk which means that burns and injuries to the skin and eyes may result from a short period of exposure to UV emitted from these products. 2 models were rated at moderate risk which means exposure to the UV from these products may cause painful eyes, tears, or thermal discomfort.
The actual hazard posed by excessive UV exposure is determined by its wavelength, intensity, distance, and time of exposure. According to the International Commission on Non-Ionizing Radiation Protection (ICNIRP)’s recommendation on 8-hours duration per day exposure limit of UV, the permissible time of exposure of 4 high risk models ranged from 30 seconds to 12.8 minutes at distance 200mm from the models. Taking the model with the shortest permissible time as an example, if the skin and eyes were exposed under the UV rays of this model for 30 seconds, this may already exceed the recommended limit by ICNIRP. The closer the distance to the devices, the shorter the permissible time.
Nevertheless, the Council reviewed the packaging, labelling and instruction manual of each model and found none of them marked their photobiological safety class. 1 model did not include any warning to remind consumers not to expose the skin or eyes or stare at the UVC directly. 5 models did not label the lifetime of the UVC lamps while 2 models did not provide the respective power information. Since the intensity of UVC will be reduced over time and while UV is invisible, hence hard to perceive, users may mistakenly believe an object has been fully disinfected and use it with peace of mind. In this regard, lifetime of UV lamps should be indicated.
The test result reflected that although UVC could kill or inactivate bacteria and viruses, its efficacy in the daily usage depends on numerous factors. As improper use or excessive exposure to UVC may cause injuries to the eyes and skin, consumers should pay heed to the following when they consider using UV disinfection devices:
- Read the product instructions carefully before use, and use in accordance with the procedures and precautions as stated;
- Do not let children use or play with these products;
- UVC effectively disinfects non-porous surfaces, whereas it is less effective on rough, porous surfaces, or if there is dirt, grease, skin and other debris on the surface of objects;
- Not all objects are suitable for disinfection by UVC. The use of UVC on objects made of plastics, rubbers (like pacifiers and infant toys) will speed up the aging of such materials, resulting in deformation, brittleness, change of colour and etc. UVC may also lead to discolouration of clothes and fabrics;
- Since both UV intensity and time of exposure affect the disinfection efficacy, while using the handheld products, consumers should place the device as close to the object as practicable and keep for a certain period of time to allow better disinfection performance;
- When using a handheld disinfection device to sanitise an object with a large surface area, complete disinfection may not be achieved due to missing out of some areas or insufficient operation time. As such, do not over-rely on the disinfection capability of these products and neglect general cleaning and disinfection in maintaining personal and environmental hygiene;
- Clean the dirt or dust on the surface of UV lamp or the LED regularly to avoid adversely affecting the UVC intensity.
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