FREQUENTLY ASKED QUESTIONS
What does UV-C or UVGI mean?
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
What is germicidal UV, and what is UVGI?
Germicidal UV (GUV) refers to using ultraviolet radiant energy to inactivate bacteria, mold spores, fungi, or viruses. When the process is applied in a given location, it has generally been referred to as ultraviolet germicidal irradiation (UVGI).
Is all ultraviolet considered germicidal ultraviolet (GUV)?
No. Germicidal ultraviolet (GUV) – refers to short-wavelength ultraviolet “light” (radiant energy) that has been shown to kill bacteria and spores and to inactivate viruses. Wavelengths in the photobiological ultraviolet spectral band known as the “UV-C,” from 200 to 280 nanometers (nm), have been shown to be the most effective for disinfection, although longer, less energetic UV can also disinfect if applied in much greater doses.
Can UV-C kill viruses as well as bacteria?
Yes, UV-C kills living bacteria, but viruses are technically not living organisms; thus, we should correctly say “inactivate viruses.” Individual, energetic UV-C photons photochemically interact with the RNA and DNA molecules in a virus or bacterium to render these microbes non-infectious.
Can UV-C effectively inactivate the SARS-CoV-2 virus, responsible for COVID-19?
Yes, if the virus is directly illuminated by UV-C at the effective dose level. UV-C can play an effective role with other methods of disinfection, but it is essential that individuals be protected to prevent UV hazards to the eyes and skin. UV-C should not be used to disinfect the hands!
How does GUV work to disinfect air?
Commonly used GUV lamps generate predominantly 254-nm UV radiant energy, which is close to the peak germicidal wavelengths of 265 to 270 nm – both in the UV-C range, compared to the longer-wavelength ultraviolet (UV-A and UV-B) in sunlight. GUV radiant energy damages nucleic acids (DNA and RNA), thus preventing replication and leading to the death of virtually all bacteria and inactivation of all viruses—both DNA and RNA types. Bacteria and viruses vary somewhat in UV susceptibility, with environmental organisms, fungal spores, and mycobacteria being relatively harder to kill than more rapidly replicating and non-environmental microbes and most bacteria. But even fungi are effectively killed with high-dose UV, which is used, for example, to treat fungal contamination of air conditioning systems. GUV can be most effectively used to disinfect air in the upper room where ceiling height permits, but can also be used in ventilation ducts and room air cleaners, as noted. As explained below, upper-room GUV is considered the most effective application for room air disinfection, where feasible.
What is upper-room GUV?
Upper-room GUV is a safe means of air disinfection that is possible in rooms with high ceilings. In this method, specially designed and installed UV-C fixtures that irradiate only the air above 2.1 meters (7 feet) constantly disinfect the upper air volume. This is most effective when there is constantly mixed air by fans and HVAC ventilation, but even without strong ventilation or fans, air constantly mixes by
movements and normal convective currents.
Are GUV lamps safe?
UVGI lamp emissions can pose a workplace safety and health hazard to the eyes and skin if the lamps are improperly used or installed. However, these lamps can be used safely if workers are informed regarding the hazards and follow appropriate precautions. Upper-room GUV has been safely used for preventing airborne transmission for at least 70 years. A great deal is known about the human exposure
limits of 254-nm UV (UV-C) irradiation. Compared to the UV-A and UV-B in sunlight, UV-C is almost entirely absorbed by the outer dead layer (stratum corneum) and outer skin (outer epidermis), with very limited penetration to the deeper cellular layers of skin where new cells are constantly created. For comparison, the current daily safety limit of 254-nm UV-C for 8 hours is 6.0 mJ/cm2, whereas less than
ten minutes of summer sun exposure at a UV Index of 10 can deliver the equivalent limiting daily safety dose (1) because of its much more-penetrating UV-A and UV-B.
Will GUV increase my lifetime risk for skin cancer?
UV-C penetrates only the superficial layers of the skin and eye, with the shortest wavelengths hardly penetrating at all to living cells (epidermis), so only a very mild, transitory “sunburn” (erythema) occurs from accidental over-exposure of skin areas. Even though GUV lamps can pose a theoretical delayed hazard, incidental UV exposures in the workplace would not significantly increase one’s lifetime risk for cataract or skin cancer when compared to daily exposure to the UV radiant energy in sunlight. Solar UV is much more penetrating and reaches the germinative (new-cell producing) layers in the skin, with the result that skin cancer risk is significant, and sunburns can be severe. There is a small amount of UV-B (297, 303, 313 nm) from a low-pressure mercury lamp, but this is insignificant unless exposures are experienced at least an order of magnitude or more above the safety limits for 254 nm. (2)
How much UV “light” is required, and how long does the process take, to disinfect a volume of air or a surface?
There are very sophisticated programs to calculate the lamp sizes and in-air dose requirements in terms of energy required for space and radiant fluence (joules per square meter, J/m2) across a cross-section of a UV-C beam, but there is a much simpler evidence-based dose that has been developed over many years for TB control, typically specified as about 17 mW of 254-nm lamp-emission radiant power per
cubic meter (m3) of space to disinfect the air.(3) Although this sounds too simplistic to be true since the air in any room is always moving and mixing, one can correctly assume that all air will be treated—the better the air mixing, the sooner this will happen. Studies at the Harvard School of Public Health(3,4) and elsewhere show log units of reduction equivalent to 24 ACH to achieve 80% reduction of transmission. Of course,100% reduction is not possible, because of the multiple modes of transmission. To disinfect surfaces, this depends on the type of surface and its cleanliness; recommended exposures vary from 200 to 1,000 J/m2 (20 to 100 mJ/cm2).(5)
Can germicidal ultraviolet be used to disinfect keyboards, phones, computer mice, etc?
Yes. Exposed solid surfaces of many devices may be sanitized by germicidal ultraviolet radiation. Please keep in mind that disinfection does not take place on internal components and surfaces. Proper precautions should be taken so that personnel will not be exposed to the germicidal ultraviolet rays. Bear in mind that some materials and plastics may degrade when repeatedly exposed to intense or prolonged ultraviolet exposure.
What are the limitations to the use of germicidal ultraviolet for air and surface disinfection?
A) Germicidal Ultraviolet rays cause harmful irritation to skin and eyes. Always wear protective clothing, gloves, and eye shield (goggles, glasses, etc.) when working with direct ultraviolet radiation. Normal tightly woven clothing will oftentimes provide adequate protection.
B) Microorganisms suspended in air or water are susceptible to germicidal ultraviolet radiation. However, germicidal ultraviolet will not penetrate most ordinary materials such as cloth, paper, ordinary glass, and most plastics. Therefore, any surface or item that needs to be exposed to germicidal ultraviolet should have a direct uninterrupted path to the rays of the germicidal ultraviolet lamp.
(1) American Conference of Governmental Industrial Hygienists. 2020 Threshold Limit Values and Biological
Exposure Indices. Cincinnati: ACGIH; 2020.
(2) International Commission on Illumination (CIE). CIE 187:2010, UV-C Photocarcinogenesis Risks from Germicidal
Lamps. Vienna: CIE; 2010.
(3) Mphaphlele M, Dharmadhikari AS, Jensen PA, Rudnick SN, van Reenen TH, Pagano MA, Leuschner W, Sears TA,
Milonova SP, van der Walt M, et al. Institutional tuberculosis transmission. Controlled trial of upper-room
ultraviolet air disinfection: A basis for new dosing guidelines. Amer J Respir Crit Care Med. 2015;192(4):477-84.
(4) Miller SL. Upper room germicidal ultraviolet systems for air disinfection are ready for wide implementation
(editorial). Am J Respir Crit Care Med. 2015;192(4):407-9.
(5) Jelden KC, Gibbs SG, Smith PW, Schwedhelm MM, Iwen PC, Beam EL, Hayes AK, Mar4on N, Kratochvil CJ, Boulter
KC, et al. Nebraska Biocontainment Unit patient discharge and environmental decontamination after Ebola
care. Amer J Infect Control. 2015;43(3):203-5.