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WHAT IS UVC? WHAT IS OZONE? |
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WHAT IS UVC? WHAT IS OZONE? |
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Just What Is
This Thing Called Ultraviolet?
The use of ultraviolet germicidal radiation to eliminate the growth of micro-organisms was pioneered by Fuller Ultraviolet Corp., and its wide applications since 1951 have placed us in an authoritative position to meet the demands of our customers. Ultraviolet germicidal energy is radiation produced by low pressure mercury lamps. The lamps are made of special glass which allows the passage of light rays emanating at 253.7 nanometers. This particular radiation has the ability to kill all micro-organisms it comes in contact with. The destruction is accomplished quickly and effectively. The UV rays strike the various micro-organisms, whether they are bacteria, virus, yeast, mold or algae, and they break through the outer membrane. The radiation reaches the heart of the organisms (commonly known as the DNA) where it causes abrupt modifications. The modified DNA transmits incorrect codes or messages, and this impairment actually brings about destruction of the micro-organisms. The World of Ultraviolet Light Germicidal light has powerful, built-in inherent determinates that, under the right design conditions, provide a means for lethal destruction of microbial organisms whether they be in air, liquids or on exposed surfaces. The ultraviolet rays emitted from germicidal tubes radiate through its chosen medium and destroy micro-organisms in their path. This propensity for destruction can be likened to the photographic effects of light in that an exposure is the product of intensity and time. In theory, such an exposure to germicidal ultraviolet rays may be obtained through a long time exposure with low UV intensities, or through a short time exposure with very high UV intensities. In practical applications, the design of a UV system is usually determined by the requirements of the job to be done with a range of up to one minute for air disinfection to a fraction of a second for liquid disinfection. Design considerations must be adjusted to secure adequate exposure times.
1. Just What Is This Thing Called Ultraviolet? There are basically four principal wavelengths in the ultraviolet spectrum that lend themselves to specific applications. These principal wavelengths are described below: a. Photochemical: which is commonly called longwave (or blacklight). This type of light is in the longer wavelength region of the UV spectrum and typically has a peak emission of about 365 nanometers. The principal uses of UVA have centered on inspection of fluorescent surfaces, body tanning, and treatment of skin diseases like psoriasis. b. Erythemal: which is commonly called UVB. UVB light is found in the middle wavelength region of the UV spectrum and generally has a peak response at 312 nanometers. The principal use of UVB lamps has been medically for the treatment of skin diseases. There is some commercial use in the aging/degradation cycles for products. c. Bactericidal: which is commonly called UVC. UVC light is found in the shorter wavelength region of the UV spectrum and generally has a peak response at 253.7 nanometers. Its primary use is for the destruction of bacteria and other micro-organisms in air, liquid or on surfaces. d. Ozone: ozone is a gaseous allotrope of oxygen and is generated photo-chemically through ultraviolet lamps. There are other ways to generate ozone such as corona discharge; however, for our purposes, we will talk about photochemical produced ozone. It is produced as a gas at 185 nanometers in the UV spectrum. Its principal use has been as an oxidizing agent and as an effective sterilant.
2. The Invisible Universe Called Microbiology Microbiology is the world of unseen life; it's a world of teeming microbial life comprising bacteria, mold spores, yeast and viruses. Each of these tiny live organisms is a microbe, yet each is very different from one another. They can be located and identified by sophisticated microscopes, and upon measurement we find these microbes are very, very small, generally about 1/25,000th of an inch. They reproduce at phenomenal rates. For instance, if bacteria reproduction was left alone, we could be inundated. Assuming a generation period of one bacterium of thirty minutes (these microbes reproduce by one cell dividing every 20 to 30 minutes) you could expect a bacterial mass weighing 10,000 tons in 36 hours! Fortunately, environmental inhibitions and other factors control microbial epidemic activity, and we are not faced with this uncontrolled growth activity. Nevertheless, some of these little "critters" play a very destructive role in contaminating air, liquids and product surfaces. Means must be provided to control this contamination, and ultraviolet germicidal lamps provide the tools for control. Later on there will be further discussion of microbial contamination.
3. Ultraviolet Germicidal Light . . . Lethal; Fatal; Deadly; Final The killing of microbes is necessary in many situations. For instance, the manufacturers of foods, pharmaceuticals and drinks are very aware of the legal and economic hazards of product contamination. Microbial contamination creates a hazard in these industries, and it is simply not limited to these locations. It is everywhere. So, how to kill them? The destruction of micro-organisms is accomplished with the UVC rays directly striking them. The kill ratio of course is dependent on time of exposure and the intensity of the UVC ray. Thus, micro-organisms that come in direct contact can be readily destroyed. However, if the micro-organism, whether it be bacteria or mold spores, is hidden below the surface, or if the microbe is not in the direct path of the rays, they will not be destroyed. If any of these conditions prevail, alternative means such as the use of photo-chemically generated ozone can be used. Generally, if you can see it, UVC won't kill it. Organisms of a size visible to the naked eye are usually too resistant to be killed by practical exposures; however, very small insects may be killed if their movement is contained, and they are subjected to a relatively long exposure time. Flying insects can be attracted to visible light generated by UVC bulbs. Their ultimate death near a UVC fixture sometimes gives a false impression of ultraviolet killing potential. On the other hand, some larvae and small worms (such as vinegar eels) are killed by UVC exposures comparable to those effective on mold spores. As a matter of interest, mold spores are very resistant to UVC kill, and it may take 10 to 100 times the intensity to kill them compared to that of common bacteria. Calculations of killing ability are not difficult providing you have all of the necessary ingredients for such lethal destruction. What do we need? Let's assume that we want to kill the Staphylococcus aureus bacterium. This particular micro-organism has the ability to withstand a certain amount of ultraviolet germicidal light energy before it finally decides to call it quits. It will require 6600 microwatt seconds of energy to level the final death blow. A typical G36T6 lamp operating at 420 m.a. will provide in excess of 778 mw/cm2 at a 12 inch distance from the lamp surface to the irradiated surface. So in the above case of our friend S. aureus, we should make the kill in about 8.5 seconds of exposure. Water-borne protozoa and amoeba can be killed with practical exposures. Many insects, such as cockroaches which are a problem in food processing and storage areas, do not like light and the UV light emitted from UVC lamps. Keeping an ultraviolet germicidal system operating 24 hours per day is an effective way to reduce both health and property hazards.
4. UVC Penetration Capabilities Penetrating, permeating, entering, perforating; no matter the description, it is an important function, and one that deserves careful consideration in designing UVC systems. UVC rays do not have great penetration ability on most substances. Obviously, in the case of air, it has a very effective killing range. Penetration is ineffective on such substances as meat, cloth, food, glass and other such "solid" materials. Consequently, air and surface irradiation are principal functions of UVC light. On the other hand, the bactericidal treatment of a liquid is very effective depending, of course, on the conditions imposed by the liquid, the methods of handling it, and the effective transmission of the UVC germicidal energy into the liquid. In the case of disinfection techniques of granular materials and powdered solids, the theory is practically the same as for high absorptive liquids. Actively stirring and agitating the surface of such materials is necessary to ensure an effective depth of agitation. Equipment must be capably designed and operated to provide for the minimum UVC germicidal transmission. Later, we'll discuss the use of an alternative method using ozone generated by UVC lamps. Ozone, as a gas, has the ability to reach those hard to expose nooks and crannies. It is an important alternative.
5. Deciphering UVC Emission Terminology There is certain nomenclature used in designing UVC systems, and a knowledge of these terms will make your understanding much more complete and effective. First of all, the UVC light source is emitted from a cylindrical tube with varying diameters, usually ranging from 1/2" diameter to 1" diameter. These tubes can be selected from a variety of sources. Refer to Section 6 for the types available. The emission intensity of a UVC germicidal light tube is usually expressed in a term called "microwatts per square centimeter" (Mw/cm2), and this creates an aura of uncertainty to those not used to such a term. So what does this actually mean? Well, the maximum intensity provided by a single tube is at its surface. So, if we calculate the surface area of the UVC lamp and only use that area which effectively emits UVC rays, we have established the "Effective Emitting Area". Simple mathematics show that the surface area of a cylindrical tube is p D L. Now if we envision effective emitting area as having a screen with squares 1 centimeter in size, the picture becomes clearer. Each of these cm2 areas now, for measurement purposes, emits a UVC lamp intensity measured in microwatts . . . thus, the term microwatts/cm2. UVC light decreasingly varies as the distance from the light gets greater. There are some involved design considerations for calculation of true intensities. For instance, many UV designers only consider the fact that intensity inversely varies as to the distance from the tube axis to the irradiated surface. This is true, but only partially since as the distance goes past a point called "effective length", there is a transition or change in the way the UVC intensity varies with distance. These considerations must be used in UVC design to provide an effective system. In actual practice, it is
possible to not only significantly increase the emitted UVC radiation by
the use of well-designed reflectors, but to control or contain the rays.
This is an especially important safety feature.
6. Germicidal Ultraviolet And Its Influence On Infection Infection, a dreaded word, is actually the spread of disease-producing organisms called pathogens. Pathogens live nearly anywhere in our everyday environment: air, water, surfaces and within the body in body fluids. Obviously, there are certain locations and occupations that have a higher risk, and this is usually found in the medical and dental environment. However, wherever people congregate, the chance of infectious transmission is highly significant. The use of germicidal devices to reduce or eliminate the threat of microbial transmission is an efficient, effective environmental method, whether the transmission is airborne, waterborne or on surfaces. Pathogens must enter the body for a person to become infected. This transmission enters the body most commonly through cuts or scrapes in the skin or mucous membranes and also by direct transmission to mouth, eyes, nose or aspiration into the lungs. Microbial contamination of food, water or other liquids also provides another causative pathway for infection. Fuller UV germicidal devices
are designed to meet the threat of just about any type of microbial
contamination in almost any environment. We suggest contacting a
Fuller-trained engineer to discuss your particular problem. 7. UVC Devices and Applications
There are many applications of ultraviolet germicidal
tubes, and these applications may range from simple fixtures that direct
UVC rays to a source of contamination to the more complicated designs. One
of the more complicated areas is animal protection. In a number of kennels
we serviced, the problem was to irradiate a particular area while moving
pathogen infested air across the ultraviolet lamps. It was a tough
design, but nonetheless accomplished, decreasing kennel cough throughout
the kennels.
Another area in which UVC is very appropriate is in
personal protection. UVC dis-infection of
There are numerous conditions which require or need non-
chlorinated water for processing.
UVC Applications
WHAT IS OZONE?
1. Ozone . . . That Awful Word Ozone . . . you've heard it almost daily in the weather forecasts. The average person thinks of it as a nasty substance, and that it is a major pollutant in our environmental involvement. As usual, erroneous media reporting has cascaded the term "ozone" into a most unpleasant word. So what is the real truth about this most remarkable substance. What is it? What isn't it? How does it work? Does it work? What does it do? Let's take a brief look at ozone. Ozone is a gaseous allotrope of oxygen, and it is known as a very strong oxidizing agent in addition to being an extremely effective sterilant. It has been commonly used for many years as a water sterilant. Many major cities use ozone for this purpose, including Moscow, Paris, Nice and, most recently, Los Angeles. In fact. L.A. has the largest ozone generating plant in the world. Ozone has been found to be extremely effective against microbial contamination of other materials. It has a unique advantage in that it is a gas and, as such, has the capability of reaching all those "nooks and crannies" to perform its odor destruction in a most efficient manner. Ozone is efficiently generated by ultraviolet radiation having wavelengths below 200 nanometers and, most specifically, at 185 nanometers. Ozone is excited by other UV radiation and is destroyed by ultraviolet emissions at 253.7 nanometers. It is noteworthy that organic molecules are also excited by ultraviolet energy across the spectrum. The most efficient design of UVC equipment uses a combination of wavelengths to achieve a balance between ozone generation, decomposition and molecular excitation. Ozone is a most useful tool by itself, and when used in conjunction with UVC, the overall decontamination process works synergistically Practical Uses for Ozone Generators The use of highly efficient, low maintenance, photochemical ozone producing systems are multifold in industrial, commercial, and in some cases, residential. While the potential scope of application is virtually unlimited, find below examples to illustrate the variation of uses. We manufacture many types of ozone devices and systems to fit virtually every level of offensive odors. Keep in mind the key to removing these odors is to extinguish them at the source while keeping living spaces around these areas virtually ozone free. Fuller ozone generators are designed to emit ozone levels below the standard .03 p.p.m. as required by the E.P.A., OSHA, and the F.D.A. .
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