High-intensity ultraviolet germicidal lamp (above)

Time: 2020.04.08Source: View: 2309

1 The importance of cutting off the spread of viruses in public places
At the beginning of 2020, an unexpected COVID-19 epidemic swept the world. According to data released by the World Health Organization on April 3, the COVID-19 epidemic has affected 205 countries and regions around the world, with a total of more than 1 million confirmed cases^[1]. The speed and number of infections in this epidemic far exceeded those of SARS and MERS, causing huge losses to human life and the global economy, and casting a huge shadow over people's lives.

The novel coronavirus is a large, enveloped, positive-strand RNA virus. Unlike SARS, which is only contagious during the onset period, COVID-19 is more cunning and highly contagious during the incubation period. The main routes of transmission are respiratory droplets (sneezing, coughing, etc.) and contact transmission (picking the nose, rubbing the eyes, etc. with hands that have been in contact with the virus)^[2], and it can survive from hours to days in different environments outside the human body. It is particularly important to effectively cut off the virus's transmission route and sterilize and disinfect crowded public places such as hospitals, airports, high-speed rail stations, and shopping malls to avoid cross-infection of the virus among the crowd. At present, the domestic battle against the epidemic has just come to an end, and we are facing the dual challenges of resuming work and production and imported cases from abroad. We need to be prepared for a long-term battle with the virus.

2 Advantages of UV light disinfection
The Public Protection Guidelines for Pneumonia Infected by the Novel Coronavirus clearly states^[2] that "the virus is sensitive to ultraviolet light and heat. 56°C for 30 minutes, ether, 75% ethanol, chlorine-containing disinfectants, peracetic acid, chloroform and other lipid solvents can effectively inactivate the virus, while chlorhexidine cannot effectively inactivate the virus."

Ultraviolet light is the general term for radiation with wavelengths ranging from 10nm to 380nm in the electromagnetic spectrum, starting at the short-wave limit of visible light and overlapping with the long-wave wavelength of X-rays. Among them, short-wave ultraviolet (UVC, 200nm-280nm) is the radiation band used for sterilization and disinfection. The national standard GB19258-2012 defines ultraviolet germicidal lamps as mainly low-pressure mercury vapor discharge lamps using quartz glass or other ultraviolet-transmitting glass. The discharge generates ultraviolet radiation with a wavelength of 253.7nm. Its ultraviolet radiation can kill bacteria and viruses. [3] However, when using it, it should be noted that direct exposure of the human body to short-wave ultraviolet can cause skin redness and eye irritation.

The principle of ultraviolet germicidal lamp disinfection is to use high-energy photons near 253.7nm (4.88eV) to act on microorganisms (bacteria, viruses, spores and other pathogens) Chromosomes (DNA and RNA) are damaged, resulting in the breakage of chromosome bonds and chains, cross-linking between strands, and the formation of photochemical products, which changes the biological activity of chromosomes and makes the microorganisms unable to replicate and then die, thus achieving the purpose of disinfection. The new coronavirus is mainly composed of protein membrane and genetic material RNA. It does not have a complete cell membrane structure. Ultraviolet rays can easily act on genetic material and destroy it, thereby preventing the reproduction and spread of the virus. ^[4,5]

Ultraviolet disinfection is a purely physical method. Compared with chemical methods, it has the following advantages:
1. High-efficiency sterilization: When the cumulative ultraviolet dose of most bacteria and viruses reaches 20mJ/cm2, the inactivation rate can be as high as 99% or more. The traditional 36W ultraviolet mercury lamp on the market currently has an irradiation intensity of about 100μW/cm2 within a 1-meter irradiation range. Continuous irradiation for 3 minutes can reach the disinfection dose.
2. Broad-spectrum sterilization: UV sterilization has the highest broad-spectrum, and it can kill almost all bacteria and viruses with high efficiency.
3. No secondary pollution: UV sterilization does not add any chemical agents, so it will not cause secondary pollution to the water body and the surrounding environment, and will not change any components in the water.
4. Safe and reliable operation: Traditional disinfection technologies such as chloride or ozone, the disinfectant itself is a highly toxic and flammable substance, but the UV disinfection system does not have such safety hazards.
5. Low operation and maintenance costs: UV sterilization equipment occupies a small area and has simple structure requirements. After installation, the automatic switch can be remotely controlled by software, and there is no need to hire special cleaning staff for on-site operation.

3 The current shortcomings of UV disinfection light sources in the market in virus prevention
The illumination of ultraviolet light is generally expressed in microwatts per square centimeter (μW/cm²). The relevant national standards and regulations stipulate^[6,7]: The radiation intensity of a new 30W UV lamp measured at a vertical distance of 1m from the center below should be greater than 100μW/cm2 before it can be used.
The ultraviolet germicidal lamps currently used in the market mainly include low-pressure mercury vapor ultraviolet disinfection lamps and UVC LEDs. The latter is not yet mature. In the short term, the mainstream product is still low-pressure mercury vapor ultraviolet disinfection lamps (power >30W lamps, intensity ≥90μW/cm2). Their emission spectrum lines mainly include 253.7nm and 185nm. Mixed spectrum products can promote the production of ozone and also have a bactericidal effect. The effect is better than that of a single 253.7nm spectrum ultraviolet lamp. The lifespan is generally about 600-800 hours. The service life of imported ultraviolet lamps is an average of more than 1000 hours.

So far, no quantitative experimental data on the lethal dose of ultraviolet radiation for the new coronavirus has been seen, mainly referring to the previous research results on SARS and MERS viruses. In 2003, Dong Xiaoping, an expert at the Institute of Viral Disease Control and Prevention of the Chinese Center for Disease Control and Prevention, led a research team that found that applying 253.7nm ultraviolet light with an intensity greater than 90μW/cm² to coronavirus can kill SARS virus in 60 minutes. In 2006, Taylor's team at the Center for Biologics Evaluation and Research of the U.S. Food and Drug Administration found that under ultraviolet light with a characteristic wavelength of 253.7nm and a radiation intensity of 4016μW/cm², a SARS virus sample with an initial TCID50 concentration of about 100^5.8/mL was partially killed after 1 minute. When the ultraviolet dose reached 1445 mJ/cm2, a killing rate of 99.99% was achieved. The 60-minute sterilization time is meaningful for laboratory research, as researchers have sufficient time to record and observe the sterilization effects of different ultraviolet exposure times. However, for the application in actual places such as hospitals, schools, and high-speed rail stations, the 60-minute sterilization time is too long, making the sterilization efficiency in space too low.

The key to UV sterilization is to significantly increase the UV light output intensity of the UV lamp. UVC LEDs are inefficient and their wavelengths are not short enough. Although they are portable, they are not ideal for disinfecting large venues. The intensity of traditional UV lamps can be increased by increasing the length of the lamp tube, increasing the weight of the mercury pellets, and increasing the power supply. In August 2017, the Minamata Convention on Mercury officially came into effect in my country. This convention stipulates that the weight of mercury in a single UV lamp cannot exceed 13 mg, which greatly limits the output intensity of traditional UV lamps. In addition, since the length of traditional UV lamps is usually greater than 500 mm^[10], for mobile sterilization, the equipment will be too large, inflexible to operate, and there will be dead corners for sterilization. The existing polarized mercury lamps cannot meet the intensity requirements for rapid and large-scale killing of coronaviruses. Therefore, a new physical excitation method is needed to significantly improve the conversion efficiency of UV light while significantly reducing the volume of the lamp tube.

References

[1] National Health Commission Statistics and Information Center Epidemic Prevention and Control Dynamics, http://www.nhc.gov.cn.
[2] National Health Commission "Guidelines for Public Protection against Pneumonia Infected by New Coronavirus", People's Publishing House, 2020.
[3] Ultraviolet Germicidal Lamp "GB19258-2012", China National Standardization Administration, 2012.
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[5]https://www.kickstarter.com/projects/740978067/cleanty-worlds-smallest-and-most-powerful-uvc-led
[6] Technical Specification for Disinfection of Medical Institutions (WS/T367-2012), National Health Commission, 2012.
[7] Hospital air purification management specification "WS/T368-2012", National Health Commission, 2012.
[8] Duan S M, Zhao X S, Wen R F, et al. Stability of SARS coronavirus in human specimens and environment and its sensitivity to heating and UV irradiation[J]. Biomed Environ Sci, 2003,16(3):246-255.
[9] Darnell M E, Taylor D R. Evaluation of inactivation methods for severe acute respiratory syndrome coronavirus in noncellular blood products[J]. Transfusion, 2006,46(10):1770-1777.
[10]Spiros Kitsinelis, Spyridon Kitsinelis, Light Sources: Basics of Lighting Technologies and Applications, CRC press, ISBN 9781138034044 - CAT# K31585, 2017.

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High-intensity ultraviolet germicidal lamp (above)