Achieving Effective Germicidal Action with UVC Radiation: A Comprehensive Guide

Fluence (UV Dose) Required for up to 99% disinfection from Viruses, Bacteria

Germicidal action of UVC radiation

UVC radiation has been proven to be highly effective in disinfecting and sterilizing various surfaces and environments. The effectiveness of UVC light in these applications largely depends on factors such as irradiance, exposure time, wavelength, and the specific microorganisms targeted. This article provides an in-depth analysis of over 400 research papers to help you answer two key questions when designing, building, or installing a UVC light system:

"How much irradiance is needed?"  "What exposure time is required?"

By understanding these factors, you can design an efficient and effective UVC light system tailored to your specific needs.

Fluence (UV Dose) Required to Achieve Incremental Log Inactivation of Bacteria, Protozoa, Viruses and Algae

We will present our recommendations by analyzing the results of 413 reasearch papers, as found in the compilation "Fluence (UV Dose) Required for up to 99% disinfection from Viruses, Bacteria, Protozoa and Algae"  that can be downloaded at the links below:

PDF: Fluence (UV Dose) Required to Achieve Incremental Log Inactivation of Bacteria, Protozoa, Viruses and Algae

Overview of Germicidal Action with UVC Radiation

The germicidal action of UVC light relies on its ability to inactivate and destroy the DNA or RNA of microorganisms, such as bacteria, viruses, protozoa, and algae. The effectiveness of this process depends on several factors, including exposuretimewavelength and irradiance.

  • Exposure or fluence (sometimes called dose), the total amount of UVC radiation that the target organisms receive, measured in millijoules per square centimeter (mJ/cm2 where 1 mJ/cm2 = 10 J/m2)
  • Exposure time: The duration for which the target organisms are exposed to the UVC radiation, measured in seconds, minutes, or hours.
  • Irradiance is the flux of radiant energy per unit area, in other words, how much of the UV radiation power (measured in W = 1000 “miliwatts” mW = 1.000.000,00 “microwatts” μW ) reaches the surface. Irradiance is measured in mW/cmor W/m2 (1 mW/cm2 = 10 W/m2) and is dependent on the radiant power, distance and dispersion of the radiation emitted by the lamp source.

 Log reduction explained

"Log reduction" is a term used to describe the relative reduction in the number of live microorganisms on a surface following disinfection or sterilization. It provides a convenient way to express the efficiency of a disinfection process. For instance, a 5-log reduction implies that the number of microorganisms has been reduced by a factor of 100,000, or a 99.999% kill rate. Here's a quick reference for log reductions and their corresponding kill rates:

Log Reductions from 1 to 5 are the most common in research papers about UV light disinfection
  • 1 log reduction means the number of germs is 10 times smaller (101)
  • 2 log reduction means the number of germs is 100 times smaller (102)
  • 3 log reduction means the number of germs is 1000 times smaller(103)
  • 4 log reduction means the number of germs is 10,000 times smaller(104)
  • 5 log reduction means the number of germs is 100,000 times smaller(105)
 
Log Reduction Kill rate of microorganisms
1 90%
2 99%
3 99.9%
4 99.99%
5 99.999%
 

Findings from Over 400 Disinfection Experiments with UVC radiation

Our analysis of the compiled data from 431 studies reveals valuable insights into the effectiveness of UVC radiation in achieving different levels of disinfection. The studies measured the fluence required to achieve log reductions from 1 to 5 for various microorganisms when exposed to different types of UVC sources, including low-pressure (LP) mercury arc lamps, medium-pressure (MP) mercury arc lamps, and UVC LEDs.

The data can be downloaded at the link below:

PDF: Fluence (UV Dose) Required to Achieve Incremental Log Inactivation of Bacteria, Protozoa, Viruses and Algae

For each pathogen, the fluence (dose) required to achieve the given log reduction is written in mJ/cm2 when exposed to the UV radiation of the test lamp. Lamps used for the tests, as detailed for each result, are:

  • LP: low-pressure (LP) monochromatic mercury arc lamp or filtered polychromatic UV light is used to achieve a narrowband of  irradiation around 254 nm
  • MP: polychromatic medium pressure (MP) mercury arc lamps
  • UVC LEDs

Tables 1-5 present a summary of published data on the ultraviolet (UV) fluence-response data for various microorganisms that are pathogens, indicators or organisms encountered in the application, testing of performance, and validation of UV disinfection technologies. The tables reflect the state of knowledge but include the variation in technique and biological response that currently exists in the absence of standardized protocols. Users of the data for their own purposes are advised to exercise critical judgment in how they use the data.

Key findings include:

In 81.90% of the studies, a fluence of less than 20 mJ/cm2 was sufficient to achieve a 90% kill rate (1-log reduction) for the analyzed microorganisms. In 8.82% of the studies, the dose needed to be increased to 30 mJ/cm2, while in the remaining 9.28%, a dose of 30 to 50+ mJ/cm2 was required.

Viruses were found to be more resistant to UVC radiation than bacteria. A fluence of up to 20 mJ/cm2 was required in 75% of the studies on viruses, while a fluence of up to 5 mJ/cm2 was sufficient in 82% of the studies on bacteria. This finding indicates that bacteria can be more easily disinfected with UVC light, which is particularly beneficial for healthcare facilities dealing with drug-resistant strains.

A 90% disinfection rate (1-log reduction) should be the primary design goal for a UVC system. Increasing the fluence to achieve a 99.9% kill rate (3-log reduction) could require, on average, a 200% increase in exposure time or irradiance per square meter. This increase can significantly affect the installation and operational costs of the system, making it less feasible for widespread use.

For a fixed budget, targeting a 90% disinfection rate could enable three times more healthcare facilities to be equipped with a continuous disinfection system. Our analysis suggests that a UVC disinfection system should aim to achieve a fluence of 20 mJ/cm2 within the planned operating time. For tight budgets or bacteria-only applications, a fluence of 5 mJ/cm2 may be recommended.

Maximum Fluence (dose) for 90% kill rate (log 1 reduction) Number of studies % of total studies
0.1-5 202 46.67%
5-10 76 17.83%
10-20 75 17.40%
20-30 38 8.82%
30-40 17 3.94%
40-50 9 2.09%
>50 14 3.25%

For a fluence of 20 mJ/cmwith an irradiance of 10W/m2 (1mW/cm2) an exposure time of 20 seconds is required, 66 seconds at 3W/m2 (0.33mW/cm2) and 200 seconds at 1W/m2(0.1mW/cm2 = 100 µW/cm2).

 

Viruses are much more resistant to UV than bacteria

All the research made on bacteria has found that a fluence of less than 12 mJ/cm2 will achive 90% inactivation, from 164 studies. In 82% of cases, as low as 5 mJ/cmis required. These results show that disinfection from bacteria can be much easier to achive with UV light, very good news for hospitals fighting with drug-resistant strains.

Viruses are significantly more resistant, requiring a fluence of up to 20 mJ/cmin 75% of the studies and up to 80 mJ/cm2 in 22%.

Pathogen Number of studies Maximum Fluence (dose) for 90% kill rate (log 1 reduction) % of total studies
Viruses 149 20 mJ/cm2 75%
Bacteria 112 5 mJ/cm2 82%

90% disinfection rate should be the UV system design goal

Based on our analysis, the following guidelines can help you design an effective and efficient UVC light system:

  • Determine the target microorganisms: Understand the specific pathogens you want to inactivate and their resistance to UVC radiation. This will help you choose the appropriate UVC source and estimate the required fluence and exposure time.
  • Choose the right UVC source: Select a UVC source with a suitable wavelength, typically between 200-280 nm, to ensure optimal germicidal action. Consider factors such as the lamp's power output, lifespan, and maintenance requirements when making your decision.
  • Calculate the required fluence and exposure time: Based on your target microorganisms and the chosen UVC source, estimate the fluence and exposure time needed to achieve the desired disinfection rate. Remember that aiming for a 90% disinfection rate (1-log reduction) can be more practical and cost-effective in most cases.
  • Optimize the system's irradiance: Ensure that the UVC system provides sufficient irradiance to achieve the required fluence within the planned exposure time. You may need to adjust the system's power output, distance from the target surface, or radiation dispersion to achieve the desired irradiance.
  • Incorporate safety measures: UVC radiation can be harmful to humans and animals. Design your system with appropriate safety features, such as timers, motion sensors, or enclosures, to minimize the risk of exposure to UVC light.

Integrate additional disinfection methods: UVC light can be combined with other disinfection techniques, such as cleaning or personal hygiene practices, to further enhance the overall effectiveness of your disinfection strategy.

UVC light has demonstrated its effectiveness in disinfecting surfaces and environments contaminated with harmful microorganisms. By understanding the factors that influence the germicidal action of UVC radiation, you can design a tailored UVC light system that meets your specific disinfection needs. Keep in mind that a 90% disinfection rate (1-log reduction) should be the primary design goal in most cases, as it provides a practical and cost-effective solution for achieving widespread use and combating the spread of pathogens.

As our analysis of the compilation shows, the UVC disinfection system is recommended to achieve a fluence of 20 mJ/cm2 in the time planned for it to function. For tight budgets or bacteria only it 5 mJ/cm2 can be recommeded.

Tables with Compilation of results in PDF

For table in excel format please contact us.
 


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