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.