UV disinfection is one of the effective methods to inactivate the COVID-19, with the advantages of high efficiency, broad-spectrum, thoroughness, non-resistance, and no secondary contamination. This paper introduces the wavelength division of UV radiation, the principle of UV disinfection, the dose of UV radiation, the UV disinfection lamp, and the UV radiation illumination. This paper introduces the wavelength classification of UV radiation, the principle of UV disinfection, the dose of UV radiation, the selection and use of UV disinfection (sterilization) lamps, and UV radiation illuminance meters.
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As stated in the “COIVD-19 Pneumonia Treatment Protocol (Trial Version 6)“, novel coronaviruses are sensitive to ultraviolet light and heat, and lipid solvents such as 56 ℃ for 30 min, ether, 75% ethanol, chlorinated disinfectants, peroxyacetic acid, and chloroform can effectively inactivate the virus. There are many types of coronaviruses, and the pathogenicity and clinical manifestations of different types of coronaviruses vary. The COVID-19 is the seventh known coronavirus to infect humans and replicate via nucleic acid (RNA). The process of disinfection by UV germicidal means mainly affects the RNA of the virus, destroying the protein layer of the virus and thus affecting its survival and replication ability. Compared with high-temperature and liquid disinfection methods, UV radiation is highly efficient, broad-spectrum, thorough, non-resistant, and non-secondary contamination, and is suitable for disinfection of indoor air, surfaces, water, and other liquids. The disadvantage is that when the dose of UV radiation (radiation energy/exposure, which is the product of radiation irradiance and exposure time) is not sufficient, it cannot effectively kill pathogens, resulting in ineffective disinfection, and improper use can also cause damage to eyes and skin. In addition, UV radiation can only be applied to the surface of the object, not to the interior of the object for disinfection.
The dose of UV radiation that can kill viruses is related to the following factors: UV radiation illumination, exposure time, environmental conditions such as temperature and humidity, the attachment of the virus to the body, and the penetration of UV radiation. This article introduces the wavelength division of UV radiation, the principle of UV disinfection, the dose of UV radiation, the use of UV disinfection lamps and UV radiation illuminance meters, and the accurate measurement and traceability of UV radiation illuminance. The correct use of UV disinfection lamps and UV irradiance meters and the reasonable control of UV radiation dose are particularly important to ensure the effective inactivation of coronaviruses.
1 Wavelength division of UV radiation and disinfection principle
Ultraviolet radiation (UV) refers to light radiation with a wavelength of 100 to 400 nm, of which the wavelength range of 315 to 400 nm is called UVA, the wavelength range of 280 to 315 nm is called UVB, and the wavelength range of 100 to 280 nm is called UVC.UV radiation in the wavelength range of 315-400 nm is called UVA, UVB in the wavelength range of 280-315 nm, and UVC in the wavelength range of 100-280 nm. Different wavelengths of UV radiation are used for different purposes, and UV radiation in the UVC band is used for disinfection. Since UV radiation in the 100-200 nm range belongs to the vacuum UV category and cannot be transmitted in the air, we often define the wavelength range of UVC in the air as 200-280 nm
Research shows that UVC radiation acts on microorganisms (bacteria, viruses, spores, and other pathogens), destroying the molecular structure of DNA (deoxyribonucleic acid) or RNA (ribonucleic acid) in the cells of microorganisms, causing DNA chain breakage, cross-linking rupture of nucleic acids and proteins, resulting in growth cell death and regenerative cell death, thus achieving the purpose of disinfection and sterilization.
UVC radiation belongs to the broad-spectrum germicidal category and can kill all microorganisms, including bacteria, tuberculosis, viruses, bacteriophages, and fungi. UVC radiation has been proven to kill viruses, and different disinfection objects do not require the same dose of UVC radiation.
2 Doses of UV disinfection
The effectiveness of UV disinfection is related to the type of virus, the disinfection environment (water or air, temperature, and humidity, flow and volume, etc.), and the radiation dose (energy). The radiation dose is the product of radiation irradiance and exposure time.
In 2004, Darnell et al. placed a UVC light source at 3 cm from the culture medium with a radiation irradiance of 4016 μW/cm² and irradiated it for 6 min to efficiently kill the SARS-CoV virus. The viral inactivation rate was 99.99% or more after 6 min of irradiation. The detection limit of virus inactivation was reached after 15 min of irradiation. As can be seen from Fig. 1, the kill rate LOG value was positively correlated with the cumulative irradiation energy (dose) and linearly correlated until LOG was lower than 4. The UV radiation dose required for a 99.99% kill rate was 1446 mJ/cm² at 105.8 /mL virus concentration. For the sterilization effect of UVA light source, Darnell et al. used a radiation irradiance of 4016 μW/cm² for 15 min and found that UVA radiation had little effect on the inactivation of the SARS-CoV virus, although it could destroy the RNA chain of the virus by combining with the photocatalyst to produce reactive oxygen species. In a study by Dong Xiaoping’s group in 2003, it was shown that 60-min irradiation at a distance of 80 cm from a UVC lamp with a radiation irradiance greater than 90 μW/cm² could effectively kill the virus, corresponding to a total UV dose of 324 mJ/cm².
Fig. 1 Effect of UVC and UVA radiation on the infectivity of SARS-CoV
Different results have been obtained in previous studies regarding the UVC radiation dose required to effectively inactivate SARS-CoV. The UVC doses were 1446 mJ/cm² and 324 mJ/cm² for different irradiance levels (4016 μW/cm², 90 μW/cm²) and different exposure times (6 min, 60 min), respectively, with a 4. 5-fold difference.
It can be seen that for different levels of UV irradiation, the UV radiation dose required for UVC disinfection varies greatly. The dose of UV radiation is closely related to the level of UV radiation irradiation. Therefore, the sterilization effect of UVC should not only consider the UV radiation dose, but also the UV radiation illumination level. Not only the UV radiation dose, but also the UV radiation illumination level should be considered. Intensity. Accurate measurement of UV irradiance and UV radiation dose is an important prerequisite for UVC sterilization. It is a significant prerequisite for UV disinfection. It is recommended that the relationship between UV irradiance It is recommended that a quantitative study of UV irradiance levels and the effect of UV disinfection of the COVID-19 be conducted as soon as possible. Furthermore, it is recommended that a quantitative study of UV irradiance levels and the effectiveness of UV disinfection of the COVID-19 be conducted as soon as possible.
3 UV disinfection (sterilization) lamps and their use
UVC sterilization lamp is an important apparatus to achieve UV disinfection. According to the definition of GB/T 19258-2012 “UVC Germicidal Lamp”, a UVC germicidal (disinfection) lamp is a low-pressure mercury vapor discharge lamp using quartz glass or other violet-permeable glass, which produces ultraviolet radiation with a peak wavelength of 253.7 nm. COVID-19 has no cell nucleus, and once it enters the body, it will hijack our healthy cells to gain the ability to replicate viruses. Once it enters the human body, it will hijack our healthy cells to obtain the ability to replicate the virus, and UV radiation can effectively destroy its molecular structure, prevent its replication and achieve the final effect of extinction. In addition, UVC LEDs are also a trend in the field of disinfection, and there are already some products used in tap water purification treatment.
There are two types of UV disinfection lamps in common use, an ozone-free type, and an ozone-based type. Ozone-free lamps emit mainly 253.7 nm UV light, which kills microorganisms by damaging and destroying nucleic acids through radiation. Ozone-based disinfection lamps can transmit not only the commonly used 253.7 nm wavelength UV light but also the shorter wavelength 185 nm. Oxygen molecules in the air absorb the 185 nm wavelength UV light and produce ozone, which is a strong oxidizing agent that can effectively kill viruses. The dispersion of ozone can make up for the fact that UV radiation only travels in a straight line and has a dead spot for disinfection. However, ozone is a strong irritant to the human respiratory system. The effect of UV disinfection is related to the intensity and duration of irradiation of the UVC lamp. The irradiance of the UVC lamp at a certain distance is a very important parameter that directly determines the effectiveness of disinfection.
When using the UV lamp, the following matters should be noted:
- Good and effective protection for the skin and eyes. UVC germicidal lamps UVC wavelength ultraviolet radiation on the human skin and eyes has greater harm, can cause skin redness, skin tumors, cause retinal, corneal burns, etc. Be careful not to look directly at the bright lamp with the naked eye to avoid burns.
- UV disinfection lamp in the relative humidity of Regularly monitor the radiation illuminance of the UV lamp, when the radiation illuminance is below the required value, the lamp should be replaced in a timely manner.
- The surface of the UV disinfection lamp should be kept clean and wiped with alcohol wipes once a week, and when dust and oil are found on the surface of the lamp, it should be wiped in time.
- Indoor air disinfection: use suspended or mobile direct irradiation disinfection to kill pathogens that may be attached to air suspensions and object surfaces. When purchasing UV disinfection lamps, the number of lamps needed should be calculated according to the power of the lamp and the area of the space. According to WS / T 367-2012 “Technical specifications for disinfection in medical institutions”, the UV disinfection lamp is suspended from the ground at a height of 1. 8 ~ 2. 2 m and the number of UV disinfection lamps installed is ≥ 1. 5 W / m³ on average, with an irradiation time of ≥ 30 min. i.e., each cubic meter of space requires a UV disinfection lamp with a power of 1. 5 W, and the number of lamps required in the space is: Housing area × housing height × 1. 5 ÷ 30 (based on the purchasing power of 30 W lamps), the results are rounded off. The room should be kept clean and dry to reduce dust and water mist, and the irradiation time should be extended when the temperature is lower than 20 ℃ or higher than 40 ℃ and the relative humidity is more than 60%.
- Surface disinfection: UV disinfection lamps can only disinfect the surface of the object, not the interior of the object, but can be spread out or hung up to expand the irradiation surface so that the surface of the object is fully exposed to UV radiation, there should be no shielding. The dose of UV radiation on the irradiated surface should be ensured to meet the standard. Different types of viruses require different doses of UV radiation to be inactivated. To ensure that the dose of UV radiation is up to standard, the radiation output of the UV lamp should be monitored in real-time using a UV radiation illuminance meter calibrated by the metrology department. It is not recommended sending the UV disinfection lamp to the measurement department for testing, because the UV lamp radiation illumination with the use of distance, its radiation output will also be decayed with the use of time, can not get real-time disinfection surface UV radiation illumination value.
- The use of ultraviolet disinfection lamps to kill microorganisms protected by organic matter and airborne suspended particles more should increase the radiation dose.
- As the UV disinfection lamp time increases, its output UV radiation illumination will continue to decline. To ensure the desired disinfection effect, the radiation output of the UV lamp needs to be monitored regularly. UV radiation illuminance meters are used to quantitatively measure UV radiation illuminance and are effectively traceable and can be used to monitor the radiation illuminance of UV lamps.
- After disinfection, open the window for 30 min. and take care of the protection when using ozone-based UV lamps. Ozone in excess of the standard strongly stimulates the human respiratory tract, causing sore throat, bronchitis, and other respiratory diseases, and can also cause neurotoxicity, dizziness, and headache, vision loss, memory loss. Destroy the body’s immune function and induce lymphocyte chromosomal lesions.
- Note that some materials such as plastic and rubber products are not suitable for UV disinfection and are prone to aging under UV irradiation.
4 Ultraviolet radiation illuminance meters and its method of use
UV radiation illuminance meter is generally used to monitor the radiation of UV disinfection lamps illuminance, which is an effective means to ensure the effectiveness of disinfection. UV radiation illuminance meter mainly consists of a detector, amplifier circuit, and display instrument. The detector mostly consists of a photodetector, a filter (band pass glass or interference The detector is mostly composed of a photodetector, a filter (band pass glass or interference filter), and a diffuser. Figure 2 shows the general structure of the UV radiation illuminance meter detector. Figure 2 is a schematic diagram of the general composition of the UV radiation illuminance detector.
Fig. 2 Illustration of general structure of UV detectors
It is very important to choose and use the correct UV radiation photometer for measurement, otherwise, it will produce different degrees of measurement error and lead to ineffective disinfection. It is recommended to wear protective glasses, protective gloves, and protective clothing when using a UV radiation meter for measurement to avoid direct UV radiation to the skin and eyes, causing unnecessary damage.
1) The choice of the wavelength range. According to the wavelength of ultraviolet radiation illuminance meter to divide, generally divided into UV-A ultraviolet radiation illuminance meter, UV-B ultraviolet radiation illuminance meter, UV-C ultraviolet radiation illuminance meter. For sterilization, purposes should decide the UVC band of ultraviolet radiation illuminance meter. According to JJG 879-2015 “Ultraviolet Radiation Illuminance Meter Calibration Regulations”, the commercial UV radiation illuminance meter on the market is mainly composed of the narrowband and wideband. Wideband UV-C: 200 ~ 280 nm Narrowband UV-254: peak wavelength λp = 254 nm ± 2 nm, peak half-height width Δλ ≤ 10 nm. After calibration by the metrology department, both instruments can be used to monitor the UV radiation output of germicidal lamps.
2) Periodic calibration. It should be measured and calibrated according to JJG 879-2015 “Ultraviolet Irradiation The measurement and calibration should be carried out according to JJG 879-2015 “Ultraviolet Irradiance Meter Calibration Procedure”. Limited by the current filter, detector and other optical components of the production process level, the purple The long-term stability of the external radiation illuminance meter is generally poor. Subject to the use of the environment, frequency of use, strong light aging, temperature and humidity, use and storage method, and other factors, the instrument’s value is easy to drift, resulting in measurement errors. This leads to errors in measurement.
To ensure the accuracy and reliability of the measurement results, the instruments need to be regularly sent To ensure the accuracy and reliability of the measurement results, the instrument should be sent to the metrology department for calibration periodically. The recommended calibration interval for general applications is one year. For general applications, a calibration interval of one year is recommended, while for special or high accuracy applications, a shorter calibration interval is recommended. Use The calibration certificate issued by the metrology department should be read carefully when the instrument is used. The calibration certificate issued by the metrology department should be read carefully, and the measurement results should be corrected according to the indicated value error or correction factor of the instrument.
3) Proper measurement method. When measuring, place the detector on the surface of the object to be disinfected. Place the detector at the surface of the object to be disinfected, so that the receiving surface of the detector is level with the surface of the object. The receiving surface of the detector should be flush with the surface of the object. Select several points evenly on the disinfection surface to ensure that the radiation illumination at each point reaches the same level. Make sure that the radiation illumination of each point is up to standard. The detector is too close to the lamp. This is because the detector has a certain cosine, The detector has a certain cosine error and does not pick up the large-angle radiation from both ends of the lamp very well. The detector has a certain cosine error and does not receive the large-angle radiation from the ends of the lamp well. Accurate measurement at close range requires a special design of detectors with good cosine performance or mathematical correction.
4) Keep the detector surface clean. When using, it is recommended to wear clean and soft gloves to protect the surface of the detector to avoid contamination of the receiving surface of the detector by oil on your hands, which will affect the radiant illumination responsiveness of the detector and cause deviation of the measurement results. When not in use, it should be covered with a protective cover to prevent dust contamination.
5) Strong UV irradiation can easily lead to detector aging. Detector components such as diffusers, filters, and detection components in the long-term irradiation of strong ultraviolet light source, it is easy to the aging phenomenon, resulting in reduced sensitivity, impacting the stability of the instrument value. Therefore, it should be avoided that the detector is exposed to strong UV irradiation for a long time, and the light is blocked when it is not measured. In the strong ultraviolet radiation, irradiation under the work of ultraviolet radiation illuminance meter should shorten the calibration interval.
6) Storage of the instrument. The detector is the core optics of the UV radiation illuminance meter, its stability is very critical to the measurement. Should pay attention to the preservation of the detector, when not in use should be placed in a dry vessel or constant temperature dry box, to avoid the impact of the wet environment on the filter.
The current narrowband ultraviolet radiation illuminance meter uses UVC interference filters, interference filters are affected by ambient temperature and humidity, the peak wavelength drift, which is the main reason for the large change in the instrument value.
Broadband filters are impacted by humidity and are easily moldy in humid environments, causing large drifts in measurement values. In the international comparison of “detector illumination responsiveness” organized by APMP in 2004, the leading laboratory did not consider the effect of humidity. The leading laboratory did not consider the effect of humidity, and the UVA was not measured and transported for two years. In the 2004 APMP international comparison of “detector illuminance responsiveness”, the lead laboratory did not consider the effect of humidity, and the UVA filter showed severe mold during two years of measurement and transportation. Additional experiments were conducted at a later stage.
5 Conclusion
UV disinfection lamps can effectively inactivate novel coronaviruses. The effectiveness of UV disinfection is determined by the irradiance of the UVC radiation received by the virus and the duration of exposure. Accurate measurement of UVC irradiance is the key to effective virus inactivation. This paper describes the use of UV disinfection lamps and UV irradiance meters and the measurement and traceability of UV irradiance in UV disinfection. The UV radiation illuminance meter provides accurate and reliable traceability standards for UV disinfection and sterilization applications and provides metrological support for the prevention and control of epidemics.
Studies have shown that the dose of UV radiation required for UVC disinfection varies greatly for different levels of UV irradiation. Therefore, the UV disinfection should not only consider the UV radiation dose as a comprehensive parameter, but also pay attention to the intensity of UV radiation irradiation. For the new coronavirus COVID-19, it is recommended to carry out quantitative studies on the effect of different UV radiation levels on inactivation of the virus as soon as possible.
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