UVGI Kills Microorganisms and Sterilizes Objects

Ultraviolet germicidal irradiation (UVGI) is one of the most versatile and effective ways of sterilizing an object without causing damage and without generating harmful by-products. Because of its versatility and safety, UVGI has been used to sterilize air, drinking water, aquariums, ponds, laboratory equipment, medical instruments, food and beverages. The beneficial uses of UV light have been known for more than a century. Niels Finsen, a Danish physician and scientist, first used UV radiation to heal tuberculosis lesions and won the Nobel Prize for this work in 1903.

UV radiation generated by our sun comes to the earth in three forms and is classified according to its wavelength: UVA, UVB and UVC. UVA and UVB radiation is responsible for sunburns and photo damage to our skin and can be blocked by clothing or sunscreens. Shortwave UVC radiation is also called ionizing radiation because it has enough energy to quickly destroy important molecular bonds such as those found in deoxyribonucleic acid (DNA), the molecular blue print of all living cells. By creating random breaks in DNA, UV radiation can introduce mutations and in most microorganisms this causes cell death. Fortunately, the earth’s ozone layer absorbs most of the UVC radiation generated by the sun and allows biological processes, in other words life, to exist on Earth. This feature of UVC can be useful, however, to kill potentially harmful microorganisms that are relatively resistant to other forms of sterilization. Ashok Gadgil was the first to use UV radiation to kill microorganisms in water and thereby use UV radiation to sterilize water.

UVGI uses short-wavelength UVC in a contained area to kill microorganisms such as viruses, bacteria and molds some of which can cause human disease and are called pathogens. Some pathogenic microorganisms are resistant to other forms of sterilization such as chemicals and often using heat sterilization is not feasible so UVGI is the only effective means of destroying them. Although UVGI kills microorganisms, it does not remove them, so adding a filtration system to a UVGI sterilization system produces sterile and purified water, free of harmful microorganisms.

Whereas other UV-based germicidal systems pass air or water through or in front of the unit, the miniZapr UVGI product line passes over the target material. As such, the miniZapr UVGI is a “line-of-sight” solution, offering an unobstructed view of the target material. When used according to specifications for speed, distance and number of passes, the miniZapr system is effective at reaching the indicated germicidal kill rates. A repeated, pro-longed treatment program can remove 99.9999% of surface microbes and a significant reduction in microbial burden. Such a high kill rate ensures that the risk of infection for human users is minimal and that the treated facilities are safe for human use.

Target Levels of UVC Energy

Each microorganism has a different level of sensitivity to UVC radiation. Some microorganisms require only a small amount of UVGI to break apart its DNA while others require more. In order to use UVGI to effectively sterilize surfaces, the operator must understand exposure levels required, the intensity of the UVC light source, the distance from the light source to the target surface and the length of time required for optimum exposure.

The miniZapr® is available in two distinct modules: the base unit and the handheld. The base unit is designed to operate 2″ from the target surface and uses eight specifically designed UVC lamps to generate 6,874 µJ/cm² of energy assuming a standard walking speed of 2 mph and three passes. The handheld module requires the operator to control all aspects of exposure such as speed, distance, and the number of passes. Assuming most users will use the handheld unit approximately 2” from the target surface, at a speed of 0.5 feet/s and in two passes, an energy dose of 7,350 µJ/cm² is reached.

In essence, greater exposure time delivers a higher dose of energy. However, the variables contributing to UVGI exposure dosage are as follows:

miniZapr® Base Module – Calculations for Various Operational Speed/Passes for Energy Exposure

Module/Cart Speed (mph) 2 1 2 1
Passes over field 3 3 2 2
Peak Exposure @ 2” (µW-s/cm²) 11,125 11,125 11,125 11,125
Total CALCULATED Dosage (µJ/cm²) 6,874 13,748 4,583 9,165

miniZapr® Handheld Module – Calculations for Various Operational Speed/Passes for Energy Exposure

Module Speed (feet per second – fps) .5 .5 .5 .5
Passes over field 2 3 2 3
Peak Exposure @ 2” (µW-s/cm²) 4,410 4,410
Peak Exposure @ 3” (µW-s/cm²) 2,940 2,940
Total CALCULATED Dosage (µJ/cm²) 4,900 7,350 7,350 11,025

NOTE: The blue highlighted columns represent the recommended basic operation.

The operational requirements of this system are flexible and users can adjust their protocols to meet their needs. Using the basic variables listed above, each user can optimize the UVGI treatment system and design a regular treatment schedule that effectively targets microbes of particular concern. For the optimum results in any setting, however, the user should be aware that a slower, deliberate delivery method delivers significantly higher levels of exposure and more effective germicidal efficacy. Of course, a higher germicidal efficacy provides greater confidence of sterility and safety.

Incident Energies of Germicidal Ultraviolet Radiation at 253.7 Nanometers (UVC) Necessary to Inhibit Colony Formation in Organisms (90%) and for 3-Log (99.9%) Reduction

Energy needed for kill factor Microwatt seconds per square centimeter

ORGANISM 90% 99.9%
Bacillus anthracis 4,520 8,700
Bacillus magaterium sp. (spores) 2,730 5,200
Bacillus magaterium sp. (veg.) 1,300 2,500
Bacillus paratyphusus 3,200 6,100
Bacillus subtilis spores 11,600 22,000
Bacillus subtilis 5,800 11,000
Clostridium tetani 13,000 22,000
Corynebacterium diphtheriae 3,370 6,500
Eberthella typosa 2,140 4,100
Escherichia coli 3,000 6,600
Leptospira Canicola-infections Jaundice 3,150 6,000
Methicillin-resistant Staphylococcus aureus (MRSA) 2,600 6,600
Micrococcus candidus 6,050 12,300
Micrococcus spheroides 1,000 15,400
Mycobacterium tuberculosis 6,200 10,000
Neisseria catarrhalis 4,400 8,500
Phtomonas tumeficiens 4,400 10,000
Proteus vulgaris 3,000 6,600
Pseudomonas aeruginosa 5,500 10,500
Pseudomonas fluorescens 3,500 6,600
Salmonella enteritidis 4,000 7,600
Salmonella paratyphi-enteic fever 3,200 6,100
Salmonella typhosa-typhoid fever 2,150 4,100
Salmonella typhimurium 8,000 15,200
Sarcina lutea 19,700 4,200
Serratia marcescens 2,420 3,400
Shigella dysenteriae-Dyentery 2,200 4,200
Shigella flexneri-Dysentary 1,700 3,400
Shigella paradysenteriae 1,680 3,400
Spirillum rubrum 4,400 6,160
Staphylococcus albus 1,840 5,720
Staphylococcus aureus (Staph) 2,600 6,600
Streptococcus hemolyticus 2,160 5,500
Streptococcus lactis 6,150 8,800
Streptococcus viridans 2,000 3,800
Vibrio comma-Cholera 3,375 6,500
PROTOZA 90% 99.9%
Chiarella vulgaris (Algae) 13,000 22,000
Nematode eggs 4,000 92,000
Paramecium 11,000 20,000
VIRUS 90% 99.9%
Bacteriophage (E. coli) 2,600 6,600
Infectious Hepatitis 5,800 8,000
Influenza 3,400 6,600
Poliovirus-Poliomyelitis 3,150 6,000
Tobacco mosaic 240,000 440,000
YEAST 90% 99.9%
Brewer’s yeast 3,300 6,600
Common yeast cake 6,000 13,200
Saccharomyces carevisiae 6,000 13,200
Saccharomyces ellipsoideus 6,000 13,200
Saccharomyces sp. 8,000 17,600
MOLD SPORES Color 90% 99%
Aspergillus flavis Yellowish green 60,000 99,000
Aspergillus glaucus Bluish green 44,000 88,000
Aspergillus niger Black 132,000 330,000
Mucor racemosus A White gray 17,000 352,000
Mucor racemosus B White gray 17,000 352,000
Oospora lactis White 5,000 11,000
Penicillium expansum Olive 3,000 22,000
Penicillium roqueforti Green 13,000 26,400
Penicillium digitatum Olive 44,000 88,000
Rhisopus nigricans Black 111,000 220,000