Because UV disinfection lamps are economical, practical, convenient, simple, and easy to use, UV as a traditional method of air disinfection is commonly used in primary hospital consultation rooms, treatment rooms, disposal rooms, etc. However, in the process of use primary hospitals do not monitor the intensity of UV radiation, etc., and then because in recent years schools are also using UV lamps for classroom air disinfection, resulting in many bad cases of burns to the eyes and face and neck, understanding the past and present life of UV lamp irradiation disinfection can help you use it correctly.
Let’s dive right in now, and you can click on the question that interest you,
1 Origin and principles of UV air disinfection
Origin of UV air disinfection. Early research began in the 1920s. It was introduced in hospital operating rooms in 1936 and first used in schools in 1937 to control the spread of rubella.
The wavelength of UV light. Wavelengths range from 400-100 nm and are divided into three wavelengths, A, B, and C. The UV-C wavelength (UV-C) is the most common wavelength. Of these, the UV-C band (290-100 nm) has the germicidal capability and is called disinfecting UVC. UVC germicidal lamps directly use UVC (central wavelength of 253.7 nm) to achieve disinfection purposes of special electric light sources.
UVC lamp disinfection principle. The UVC disinfection lamp is a low-pressure mercury lamp that uses a low-pressure (<10-2Pa) mercury vapour to be irradiated with UV light for disinfection. Both of these wavelengths are very effective in disinfecting bacteria, with the former acting directly on DNA, the genetic material of biological cells, causing DNA damage and leading to bacterial death, as well as decomposing ozone; the latter, by acting with oxygen in the air, produces a strong oxidizing effect. The latter is able to kill bacteria by interacting with oxygen in the air to produce ozone, which has a strong oxidizing effect.
2 The difference between UV disinfection lamps and ordinary fluorescent lamps and energy-saving lamps is that
The lamps of ordinary fluorescent lamps and energy-saving lamps are made of ordinary glass, which cannot transmit ultraviolet light and is absorbed by phosphor and then emits visible light, whereas the lamps of UV disinfection lamps are made of UV-transparent glass or quartz glass, which can transmit ultraviolet light through the glass tube wall.
UV lamps are a non-coherent light source and do not interfere when two beams of UV light intersect. The intensity of radiation at any point in the spatial radiation field formed by multiple UV lamps satisfies the principle of superposition. The UV radiation intensity at a point in space is inversely proportional to the square of the distance from the UV lamp, so the disinfection effect of the UV lamp is mainly concentrated within 1.0 m.
3 UV lamp subtypes and technical requirements for UV lamps
The shape can be divided into double-ended lamps (indicated by S) and single-ended lamps (indicated by D) and self-ballasted lamps (indicated by Z) three categories.
According to whether ozone is contained or not, they are divided into two types: ozone-containing (indicated by Y) and ozone-free (indicated by W).
The technical requirements for UV lamps are mainly regulated in the following areas: (1) requirements for medical electrical safety; (2) requirements for product performance safety, mainly for ozone residues or leakage, and for UV contact; (3) health and safety indicators, increasing the evaluation of disinfection effects; (4) requirements for environmental testing; and (5) improvement of the original test methods.
4 How to properly understand UVC germicidal lamps?
GB19258-2012 “UVC Germicidal Lamps”, section 4.1 Classification and Marking: Lamps can be divided into double-ended lamps (indicated by “S”), single-ended lamps (indicated by “D”) and self-ballasted lamps (indicated by”Z”) according to their shape. Z” indicates); according to whether the ozone type is divided into ozone-containing (to “Y” indicates) and ozone-free (to “W” indicates) two kinds.
5 Scope of application, method, intensity and disinfection time
Scope of application: For disinfection of unoccupied indoor air, UV lamps should not be used when the room is occupied. UV air disinfection can be divided into indoor hanging irradiation methods or mobile direct irradiation and duct internal irradiation methods. 30W UV lamp, its intensity at 1.0m should be >70μW/cm², ≥1.5W/m³.
Duration of UV lamp disinfection. When disinfecting indoor air with UV lamps, 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 <20°C or >40°C, or when the relative humidity is >60 %.
6 Influencing factors of UV lamp disinfection
1. Influence of mobile crowds
The experimental study on the relationship between UV air disinfection time and disinfection effect variables showed that the bacterial content of the air in the dispensing room did not exceed the standard immediately, 0.5h and 1.0h after disinfection without crowd flow, while the amount of bacterial contamination in the air in the buffer room with crowd flow rose quickly.
②Yang Cui-fang et al. “Exploration of the effective time of air disinfection”, air sampling by plate sedimentation method before, 0.5, 2h and 6h after disinfection in infectious disease rooms, and bacterial counting after routine incubation. Air disinfection was shown to be effective, with a short UV maintenance time in the presence of air movement after disinfection.
③ Lu voiced no statistical significance to UV, triple oxygen disinfector, circulating air disinfector in the static state of the three air disinfection methods.
2. Effect of temperature and humidity
(1) Disinfection of indoor air. Stationary air at an ambient temperature of 20°C has the greatest radiation output. When the air temperature is higher or lower, it affects the heat exchange between the lamp surface and the air, which in turn affects the temperature field inside the lamp, reducing the radiation output. Air contains water vapour and as water molecules can absorb UV light, higher air humidity will weaken the penetration of UV light and reduce the disinfection effect. When the humidity is 70%, 80% and 90%, the radiation intensity needs to be increased by 50%, 80% and 90% respectively in order to achieve the same effect.
(2) Disinfection of the air in the duct. When the air temperature is 24°C, the flow rate is 0.472m/s and the relative humidity is in the range of 35-85%, the radiation intensity of the UV lamp is inversely proportional to the moisture content of the air.
Therefore, the power of the UV lamp should be increased when the humidity is high. Air temperature and humidity affect the radiation output of the UV lamp.
3. Air flow rate influence
(1) For indoor UV lamp suspension irradiation method. Air velocity increases, will strengthen the indoor air mixing, increase the lower room microbial particles into the upper space of the opportunity to improve the sterilization rate; but at the same time, the air velocity is too large, will shorten the microbial particles in the effective range of ultraviolet radiation retention time, so that the sterilization rate is reduced.
(2) For central air conditioning duct irradiation method. Increased air flow will strengthen the cooling effect of the UV lamp, reducing the internal temperature of the lamp and reducing the radiation output.
4, ballast impact
The baseline ballast has a stable voltage/current ratio at the rated frequency and is relatively unaffected by changes in temperature, current and the surrounding magnetic field. Tao Xidan and other monitoring found that the use of different ballasts had a significant impact on the irradiation intensity of the UV lamp. Therefore, in their daily supervision, the sensory control staff should strengthen their guidance on the correct use of UV lamps in the department to reduce the influence of ballasts and other factors on the effectiveness of UV disinfection.
5. Influence of UV combined with chemical disinfection methods
The results of a Lancet study showed that for end-of-life disinfection in high-risk wards, the use of standard chemical methods plus ultraviolet light (UV-C) significantly reduced the chance of multi-drug resistant bacteria and Clostridium difficile infection in patients re-entering the ward.
6. Ozone requirements
Initial Ozone Output Rate: The initial ozone output rate for non-ozone lamps should be less than 0.05g/(KW-h). With ozone lamps the initial ozone output rate should be no less than 80% of the nominal value.
The use of UV disinfection lamps requires attention to safety, such as ozone residue or leakage over a certain concentration (0.16mg/m3 according to GB/T 18883-2003 “Indoor Air Quality Standards”) will cause harm to humans, too much UV exposure will lead to cataracts, skin cancer, etc., so pay attention to ventilation after disinfection
UVC radiation illuminance monitoring in use, 1m from the surface of the germicidal UVC lamp normal to the lamp without reflective cover measured unit area to 253.7nm as the main wavelength of UVC radiation illuminance, the unit is uW/cm².
Instrument method: After turning on the UV lamp for 5min, the UV irradiation meter probe with the measurement wavelength of 253.7nm is placed in the centre of the vertical distance of 1m under the examined UV lamp, after the instrument is stabilised, the data shown is the radiation illuminance value of the UV lamp.
Indication card method: After turning on the UV lamp for 5min, place the indication card at a vertical distance of 1m under the UV lamp, with the pattern side facing upwards, irradiate for 1min, observe the colour of the indication card block and compare it with the standard colour block.
As the UV irradiation meter needs to be calibrated annually, it is not as easy to use as the indicator card, so most medical institutions use the indicator card method to monitor UV radiation intensity, but I have visited many hospitals/clinics and found that there are phenomena of false positive results due to excessive exposure time.
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