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Sterilization principles


-Purging Light use so-called UVC to sterilize-

The unit is using the ultraviolet radiation with 253.7nm wavelength emitted by the provided UV-C lamp tube to irradiate the pathogens on surfaces of objects or in environment, then to destroy their genes, and thus to make them losing the ability of reproduction or even dead, so as to sterilize on surfaces of objects or in environment.

 

 -How to UVC sterilization?-
 Ultraviolet radiation effects on  nucleic acid (DNA and RNA) of  microorganisms and detroy their  structures, and it also effect on  the components of organisms such  as proteins. As shown in figure,  after DNA of microorganisms has  been irradiated by UVC, two  adjacent thymines become thymine dimers. The thymine dimer is very stable, so these flawed DNA can be accumulated. If thevolume of these flawed DNA is big enough, the duplication of DNA will be suppressed.

 

 

 

Ultraviolet radiation effects on RNA as it effects on DNA. Two adjacent uracils of RNA will become uracil dimers after irradiated by UVC.

The right figure shows the absorbance of thymine and uracil related to wavelength of ultraviolet radition.

The right curves is for thymine of DNA and the left curve is for uracil
of RNA.

 



-UVC Radiance Output-

UVC Radiance Output is to evaluate the power of a UVC source. The UVC Radiance Output of the UVC lamp with 253.7nm wavelength is the output of power at 253.7nm wavelength. The unit of UVC Radiance Output is wattage. It differs from the lamp's power consumption, though they have same units. Do not be confused!

-Irradiance -

Irradiance is to evaluate the intensity of irradiation of an object that is irradiated by some radiation. Irradiance is the radiance output per unit area of the surface of the object irradiated by some radiation.
The unit irradiance : W/m2, mW/cm2 , μW/cm2


< 1 W/m2=0.1mW/cm2=100uw/cm2
>

 

-Radiant Exposure -

Radiant exposure is to evaluate the cumulative energy of irradiation of an object that is irradiated under a period of time by some radiation.
Radiant Exposure is the cumulative energy per unit area of the surface of the object irradiated by some radiation.
The unit of radiance exposure : J/ m2(Wsec/ m2), mJ/cm2(mWsec/ m2), μJ/cm2(μWsec/ m2)

< 1 J/m2 = 0.1 mJ/cm2=100 μJ/cm2 >

< radiant exposure = irradiance x exposure time ( second ) >

 

-Dose For Inactivation-

When using 25 3.7nm UVC radiance to eliminate pathogens, the radiant exposure needed to cause certain percentage of all the pathogens not activating normally is called the dose for such percentage inactivation.
D90:the dose for 90% inactivation (or 10% survival)
D99:the dose for 99% inactivation, & D99=2xD90 ( refer A Genomic Model for the Prediction of Ultraviolet Inactivation Rate Constants , Wladyslaw J. Kowalski, William P. Bahnfleth, Mark T. Hernandez)

-Compute Irradiance-

You may use UVC radiometer to detect the irradiance of a point irradiated by UVC radiance. If you do not have UVC radiometer, you may also calculate the approximate value of irradiance as long as you know the distance between the point and UVC radiance source. Usually the irradiance at each direction of a radiation source is not the same. But we may assume it being uniformly distributed, this means we assumed the irradiance of the point at each direction is the same as logn as the distance between the point and radiance source is the same.


-Use of effectiveness-

In a space with a UVC radiance source,

- R represents UVC radiance output of the UVC radiance source
- d represents the distance between a point in the space and the UVC radiance source

If the exposure time is fixed, the radiant exposure E is inversely proportional to d2.

As shown in figure, choose a point in the space such that it is d away from the UVC radiance source. Assume the radiant exposure is 1Ed at that point after exposed to the UVC radiance source for a period of time. We may find from the curve in figure, the value of radiant exposue become biger when the distance d become smaller.

As shown, when the distance is 0.5d, the value of radiant exposure is four times the original one, that is 4Ed; And when the distance is 0.2d, the value of radiant exposure is 25 times the original one, that is 25Ed.

-Below:the USA study that using UV System can reduce 76% of being infected.-


-Below:another study that if using UV Systems to sterilize the air, it also accepted 70% of being infected.-


 

 





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