What is UVC?
UV-C is one of many electromagnetic frequencies emanating from the sun. Like other of these waveforms, its properties are unique to its wavelength. To synthesize this frequency, a glass tube is evacuated and refilled with argon at far below atmospheric pressure. Added to this is a small amount of mercury. When the mixture is energized (excited) it creates a glowing plasma of electrons that pass through the mercury vapor. As they strike mercury atoms, a mercury electron is liberated at a frequency representative of mercury’s spectral line, which is 253.7nm. The dominant emission (>90%) from these lamps is UV-C energy. The "C" frequency of the electromagnetic UV family has, amongst other things, germicidal effects. This was so important that Westinghouse quickly commercialized the low-pressure mercury vapor "germicidal" lamp in the early 1930's. Its humanitarian value has had worldwide success since.
We’re exposed to parts of the UV spectrum while outdoors. Generally, excessive UV exposure can produce adverse effects depending on wavelength, type and duration, and UV response differences between individuals. The three basic wavelengths:
o UV-C - includes the germicidal wavelength of 253.7nm and is used for air and water disinfection. Human overexposure causes temporary skin redness and harsh eye irritation, but no permanent damage, skin cancer, or cataracts.
o UV-B - is a narrower but more dangerous band of UV. Prolonged exposure has been associated with skin cancer, skin aging, and cataracts (clouding of the lens of the eye).
o UV-A - is more predominant outdoors than the other two. It helps to tan our skin and is used in medicine to treat certain skin disorders. It is generally a harmless wavelength. UVA, B and C will damage collagen fibers and accelerate skin aging. Generally, UVA is least harmful; UVB contributes to DNA damage and cancer. It penetrates deeply but does not cause sunburn. Because of no reddening (erythema) it cannot be measured in SPF testing. There’s no good clinical measurement of UVB blocking, but it is important that sunscreens block both UVA and B. UVC however, penetrates superficially and has not been associated with long term tissue effects.
Microorganisms are simple organic structures that readily absorb the UV-C wavelength, causing photo-disassociation (destruction). A microbes DNA (deoxyribonucleic acid, is first to be adversely effected due to its weaker molecular bonds. In hundredths of a second it suffers irreparable damage. The subsequent loss of genetic instructions causes cell death and/or the inability to replicate, rendering them harmless. Continuous exposure causes uninterrupted degradation, such as the sun does, only significantly faster.
Yes, scientific and anecdotal references abound for UV-C’s efficacy both in literature and in reports of field applications. Of the government reports, NIOSH, OSHA, CDC, GSA, EPA are the most notable. Science in the public forum comes from the University of Cincinnati, Tulsa University, University of Colorado and McGill University (Canada) to name a few. The two labs conducting independent testing and showing very favorable results are ARTI and Battelle. The list of prestigious field studies are too numerous to mention. UVC is used worldwide, more in other countries per capita than in the US. Much of this broader use is for the disinfection of drinking water and treatment of sewage in waste water treatment.
The letters "UV" relates to the magnetic wavelength spectrum known as UltraViolet light. This spectrum is more often broken down into four categories: Vacuum, Short Wave, Middle Wave and Long Wave’ or VUV, UVC, UVB & UVA. UVC is the frequency that is the most germicidal and the term UVGI refers to "Ultraviolet Germicidal Irradiation" as used by Federal Agencies such OSHA, NIOSH, GSA, EPA and the CDC when referring directly to UVC.
No, but UVC does provide exceptionable conditioning of the air much like the sun does outdoors. UVC fixtures are an air conditioning component that’s in addition to other system parts. Those include the filters, coil, heating core, fan, dampers, humidifiers, etc. All are designed to provide a specific function in the job of processing air for occupied spaces.
No, a UV-C fixture is an air conditioning component that is in addition to other system parts. These include the coil, heating core, fan, dampers, humidifiers, filters, etc. All are designed to do some form of work within the air handler a UV-C fixture is just one of these components.
Yes, in varying degrees depending on their rated efficiency. Note that for an anticipated infectious disease application, the type, efficiency and location of a filter should be of major concern. For microorganisms, the filters goal is to provide a reduction in the total number of viable microbes per "unit volume of air" downstream of it. Fortunately, some filters can also be utilized with UV-C in an approach referred to as "catch and kill". With the proper filter, UVC can kill and/or degrade what the filter has caught. Thus, for a given microbe and its products, the filters effect can be an integral part of the resulting concentration in a space. It should also be note that viruses can be as small as 0.02 microns so the target organism needs to be known so as to provide a predictable result. Additionally, a filter system can’t abate microbial growth on surfaces, in drain pans, or in plenum's and ductwork, UV-C is the tool of choice here.
For IAQ, improved heat transfer, reduced maintenance and odor, an approach used for well over ten years is to put the lamp row centerlines on 30 - 45" centerlines. Most highly regarded manufacturers have software that can size these types of installations, and more. Only consult one of these reputable manufacturers when sizing infectious disease agent applications.
Not at all. Simple installation instructions are provided along with layout drawings populated with all the necessary dimensional specifics. Product designs are emerging that allow installation of UV-C in AHU’s in under an hour in many cases! This also includes fan-coil, unitary and rooftop units, the hardest systems to keep clean. Consult a reputable factory and then involve them in any infectious disease application.
UV Resources’ fixtures are designed specifically for installation in HVACR systems, and applications. In existing equipment, microbial infestations are common. Anywhere moisture intermittently or continuously forms. Simple testing bears this and its eventual remediation out. Best results are obtained when the UV-C is located close to the offending surface. Fixturing is generally installed from 6" to up to 50" away from the surface to be irradiated. This way the application is sure to degrade and eliminate surface and waterborne contamination.
Results are obviously more dramatic when you don't but it really gets down to time. UVC will degrade organic material on, and often within a surface in a time frame unique to the type and amount being removed. But usually within 180 days or less. Once the contaminants are known, UV Resources might help you make that decision. Generally, cleaning first is done to hasten the cleanup process. Where the contamination is unknown, it is wise to irradiate the contaminants for at least 30 days and fully gowning before disrupting them.