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.
Is UVC Harmful?
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.
Does it work?
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.
How does it effect germs?
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.
What does UVC or UVGI means?
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.
Do UVS lamps produce ozone?
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.
How do you size UV-C applications?
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.