First of all, we must know that there are three types of ultraviolet (UV): UVA (longwave), UVB (medium wave), and UVC (short wave). Among them, shortwave UVC can effectively kill viruses, so most ultraviolet disinfection lamps are shortwave with a wavelength of 254nm Ultraviolet rays.
Secondly, there is a well-known saying: "Aside from the dose and the toxicity, it is a hooliganism." In the same way, even if there is 254nm ultraviolet light, we must know how strong the exposure intensity and how long the exposure time is needed to eliminate the coronavirus, otherwise the dose is not enough to kill the virus. , Too high a dose and waste of resources and time, this is very important. Determining the effective anti-virus dose is the biggest part of my review time. Unfortunately, even though it is said in many places that ultraviolet rays can eliminate the coronavirus, there is basically no reliable guidance to tell us how to do it. Most of the existing science on the Internet does not clearly specify the operation method and the required dosage of ultraviolet rays. , Even the latest antiviral guidelines published by the Chinese Center for Disease Control and Prevention only say that “ultraviolet rays can inactivate human coronaviruses”, but does not mention how strong the ultraviolet rays can be.
If we want to buy UV lamps at will, various UV disinfection tools with different powers and different types will bring us great difficulty in determining the effectiveness of antivirus. Some say it takes 30 seconds, some say 15 minutes, and some say 30 minutes. , Unable to find reliable data, our previous efforts will be meaningless. So I checked many documents carefully, and finally found two studies that I think can be used as reliable references to help me ensure that the sterilization box I made is sufficient to kill the virus. These two studies studied the inactivation efficiency of ultraviolet rays on Ebola, MERS that raged in 2012, and SARS coronavirus in 2003.
Based on the data of these two studies, I roughly estimated that the time needed to kill the virus for the disinfection box I made was 5 minutes.
The following is the basis and process of the calculation: First of all, we need to know that the three parameters to be considered for ultraviolet disinfection are: irradiation intensity (μw/cm2), irradiation time (s) and irradiation distance (cm), where the irradiation distance and intensity are negative Related, that is, the closer the same UV light source is, the higher the irradiation intensity of the contact surface.
Another way to express the antiviral dose is to use the exposure per unit area (J/cm2), which means that as long as the exposure per unit area of the virus accumulates to a certain level, the virus will lose its activity, and the exposure can be adjusted by adjusting the exposure intensity And time will come. In the two studies, the ultraviolet radiation dose required to kill the virus is: In the first study, the UVC ultraviolet lamp used by Duan et al. has an irradiation intensity of 90μw/cm2 and an irradiation distance of 80cm. The experiment shows that the SARS virus is in The activity under different irradiation time is:
It can be seen that the SARS virus will no longer be detectable after 60 minutes. In the end, the researcher gave the radiation required for SARS virus inactivation to be about 162000μw·s/cm2. Remember this key data, which will be used later. In the second study, Erikmann et al. studied the inactivation efficiency of ultraviolet rays on Ebola virus and MERS virus, and they directly used the experimental results shown by exposure:
It can be seen that when the exposure reaches 0.15J/cm2, both viruses lose their infectivity. In addition, a new study published this year by the author of this study also concluded that ultraviolet radiation with an exposure dose of 0.1-0.15J/cm2 is enough to make the SARS virus lose its infectivity. Now we know that 162000μw·s/cm2 and 0.15J/cm2 The amount of exposure can kill the coronavirus. For the convenience of comparison,
Let's convert the second data unit:
0.15J/cm2 = 150000μw·s/cm2
So we are confident that:
"When the exposure reaches 162000μw·s/cm2, the coronavirus can die out."
With this key data, we can calculate the shortest exposure time for disinfection, because most UV lamps are marked with exposure intensity (unit is μw/cm2).
For your convenience, converted to minutes:
162000μw·s/cm2 = 2700μw·min/cm2
Therefore, the formula we most need to know is:
Minimum disinfection minutes = 2700 / irradiation intensity when close
Assuming that the irradiation intensity in the close situation is 500μw/cm2, the shortest irradiation time is 2700/500=5.4 minutes. The core basis of my previous production process and disinfection method is this formula. When we know how to operate to achieve the disinfection effect, the phrase "Ultraviolet rays can be disinfected" has practical value.
Sincerely, it is my personal efforts to extend the use time of masks safely and effectively when the mask is in short supply. I hope it will be helpful to everyone. I am not a medical professional. There may be omissions and omissions in the inspection and production process. If there is any error, please ask professionals to correct it. I will correct it in time.
How to do UV disinfection? - Safeagle
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