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 photo-biological ultraviolet spectral band known as the “UV-C,” from 200 to 280 nanometers (nm), have been shown to be the most effective for disinfection. UV-C wavelengths comprise photons (particles of light) that are the most energetic in the optical spectrum (comprising UV, visible, and infrared) and therefore are the most photo-chemically active.

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 photo-chemically interact with the RNA and DNA molecules in a virus or bacterium to render these microbes non-infectious. This all happens on the microscopic level. Viruses are less than one micrometer (µm, one-millionth of a meter) in size, and bacteria are typically 0.5 to 5 µm.

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 as elaborated in Section 4. UV-C should not be used to disinfect the hands!

No. UV-A and longer (visible) wavelengths do not have germicidally effective emission wavelengths to inactivate viruses. Their relative disinfection capability is very minimal on the order of 1,000 times less effective in terms of fluence rate than the low-pressure mercury germicidal lamp. There have been only very special applications of wavelengths in the UV-A and violet (e.g., 405 nm), which require very high doses not practical in an occupied environment and were not recommended for viral sterilization. The trace amount of UV-B that is emitted from some white-light fluorescent lamps probably has similar efficacy.

Light-emitting diodes (LEDs) have been available for some time in the UV-A region. The advantage of UV-A or visible-light LEDs would be that they can easily be incorporated into LED-based luminaires, and there might be no need for protective gear. However, the efficacy of violet or UV-A energy that is not harmful to the skin or eyes is minimal.

Yes, particularly in the late spring and early summer when the sun is high in the sky and the UV index is high. At a UV Index of 10, the duration to achieve at least a three-log kill of bacteria (99.9% killed) is estimated as less than one hour.

This is important, but difficult to answer in a simple fashion and it depends on how the microbes were made airborne, e.g., from a sneeze or cough, or by being blown up from surfaces or dusted off clothes. The smallest particles (1- to 5-µm droplet nuclei) can remain airborne much longer than cough droplets—for many minutes or even hours.

Diagnosis of infectious cases and their isolation is a critical intervention, but transmission from asymptomatic persons is believed to play an important role in community transmission. In the U.S., the Centers for Disease Control and Prevention (CDC) has recommended that everyone wear non-medical face covers to reduce spread by respiratory droplets, both large and small. Healthcare workers should wear well fitted respirators designed to exclude airborne particles, in addition to following all contact precautions. For the airborne component, ventilation, social distancing, and other means of air disinfection are expected to have a role. Natural ventilation outdoors and in homes can be highly effective where conditions are optimal in terms of airflow and temperature. Mechanical ventilation can be effective, but 6 to 12 air changes per hour (ACH) are recommended in general for air disinfection or dilution.

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) by causing mutations that prevent replication, thus 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.

Yes. Some hospitals have used portable GUV fixtures as mentioned in the introduction to disinfect air and surfaces in unoccupied rooms as a supplemental control measure to reduce the spread of healthcare associated infections.

Medical treatment facilities are using GUV in three primary ways: 1) upper-room GUV fixtures with air mixing, for controlling airborne pathogens in an occupied space; 2) mobile GUV units, to disinfect high-touch surfaces; and 3) GUV in HVAC air handling units, to treat recirculated air and to reduce mould growth on cooling coils. Mobile GUV units were used in the People’s Republic of China in response to COVID-19.

The most fundamental concept in photobiology is the action spectrum (or relative response) for a given effect. This action spectrum extends from 235 nm to 313 nm and peaks at approximately 265 nm. A wavelength of 254 nm has a relative efficacy of 0.85; by contrast, 313 nm in the UV-B has a relative efficacy of only 0.01.

 

Hydrogen peroxide (H202)-vapor disinfection has been the most recommended method now in use.However, if this is not available, studies by several laboratories have shown surprisingly effective UV disinfection despite the fact that UV photons will not have a straight-line pass through all the porous filter structure. Therefore, forward-scattered photons have to penetrate the mask, and substantial doses are required. This should only be attempted within a light-tight enclosure. In the U.S., NIOSH and the FDA have issued temporary guidance on this important subject.

Hand-held, compact GUV products (see Figure 4-1) have been marketed for more than a decade for disinfecting small objects such as cell phones. Most of these emit less than 2 mW/cm2 of 254-nm UV-C at contact (ours is > 12W/cm2 per bulb), meaning that the wand has to be held to the surface for several seconds for an effective multi-log unit disinfection. Waving it over an object such as a postcard for one second will not provide reliable disinfection. These products typically employ a safety switch that senses when the emission is not directed downward (away from the eyes) and shuts off if turned upward. Even if safely used, these might provide a false impression of effective disinfection.

To ensure the safe use of UVGI lamps for surface disinfection, follow these guidelines:
• Cleaning staff should place temporary warning signs at access points to the area being disinfected. They should either vacate the area during disinfection or place opaque barriers between the UVGI lamp and room occupants. If these areas are required to be occupied during disinfection and exposures cannot be avoided then personal protective equipment (PPE) should be used.
• Low- and medium-pressure mercury lamps, UVGI LEDs, and far UV-C lamps. Workers should wear plastic or glass face shields to protect the eyes and face, nitrile gloves or work gloves to protect the hands, and full-coverage clothing with tightly woven fabrics to protect all other exposed skin.
• Pulsed xenon arc lamps. Workers should wear welding or cutting goggles to protect the eyes, nitrile gloves or work gloves to protect the hands, and full-coverage clothing with tightly woven fabrics to protect all other exposed skin.

Low- and medium-pressure mercury UVGI lamps emit UV energy that poses a hazard to the cornea and skin. Some UVGI LED devices emit near 270 nm, which poses a hazard to the cornea and skin. “Far UV-C” lamps that emit around 222 nm can pose a hazard to the cornea, and recent studies have been inconsistent regarding whether far UV-C lamps pose a significant skin hazard. Differences may be the result of different glass envelopes allowing some longer-wavelength radiant-energy transmission.

Pulsed xenon arc UVGI lamps emit UV and visible radiant energy that poses a hazard to the retina,cornea, and skin. Some pulsed xenon arc lamps are filtered so that only the UV energy for disinfection is emitted. Xenon arc lamps can also pose additional safety hazards if they are not maintained properly.

These GUV lamps are generally used only in industry, to sterilize food and pharmaceutical containers, for example, but also have been used in GUV devices for hospital room disinfection. Maintenance and service should only be performed by authorized persons.

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.

No, not for safety if they are normal 254-nm UV-C lamps. Glass windows block potentially hazardous UV-B and UV-C transmission. Glass windows should be covered if pulsed xenon lamps are in use.

The most practical method of generating germicidal radiant energy is by passage of an electric discharge through a rare gas (usually argon) at low pressures (on the order of 130 to 400 pascals, or 1 to 3 torr) containing mercury vapour enclosed in a special glass tube with no fluorescent coating that transmits short-wavelength UV. Hot-cathode germicidal lamps are identical in shape, electrical connection, operating power, and life to standard fluorescent lamps, both linear and compact types. Maintaining the transmission of the lamp over life is more difficult than for standard fluorescent lamps. Cold-cathode germicidal lamps are also available in various sizes, usually for shorter, smaller diameter lamps. Their operating characteristics are similar to those of hot-cathode lamps, but their starting mechanisms are different
Approximately 45% of the input power from such a device is emitted at a mercury-discharge wavelength of 253.7 nm, in the middle of the UV-C band. The second major emission line is at 184.9 nm, but this emission is normally absorbed by the glass, since—if emitted through the glass, as it is with pure quartz—it would create ozone at levels far above the safety limit.

Medium pressure mercury (Hg) lamps are also used, particularly in water purification. Such lamps resemble high pressure mercury lamps—i.e., are much more compact—and use a clear or doped quartz envelope, depending on application.
Other sources, such as rare gas-halogen (e.g., krypton-chlorine, Kr-Cl) discharge, have been shown to produce significant emission in the far UV-C region (205 to 230 nm). The advantage of sources such as those emitting 207 nm or 222 nm, is that the deactivation rate of some bacteria and viruses appears to be relatively high, and the effect of the emission on human skin and eyes is much reduced compared to the 253.7-nm mercury emission. However, depending on the glass envelope, small but significant levels of longer wavelengths may be of concern. At this time, such sources have been developed in the research laboratory, but their presence in the marketplace is still very limited in comparison to that of mercury lamps, and there is little experience yet with any widespread use.

There are reports of companies developing LEDs that emit in the longer-wavelength UV-C region, generally at 265 to 270 nm but it’s likely to be a considerable time before commercially viable systems are brought to market.

There are a number of dedicated meters available; however, a wide range of scale is normally required, e.g., a range from 0.1 to 100 microwatts per square centimeter (µW·cm-2).
Safety readings require the lower range, and efficacy requires a range up to at least 10 mW·cm-2. A common practice is to have two calibrated meters: one in reserve and for reference. The two instruments should be periodically compared. The user should retain the manufacturer’s instructions, including a description of the meter, its safe use, and maintenance and calibration of it. Some healthcare facilities contract with a full, outside maintenance contractor that uses calibrated meters and correctly and safely replaces burned-out lamps. Some users retain a simple, less precise meter for staff to use, but the installer uses a professional meter.

The original idea on the need for this came from a general request for help to supply this type of unit from a Thoracic and Transplant Consultant Surgeon in the Mater hospital in Dublin. Among her initial comments to us was “They should be in every GP practice and hospital in Ireland”. In regard to the second part of your question, it’s important to point out that this is not a silver bullet solution and does not remove the need for standard deep cleaning as occurs now. What our unit does is that it lifts the level of clean, provides an additional layer of protection for workers and room users, adds security before and after deep clean through the removal of virus and bacteria still left behind after cleaning. The continuous and regular outbreaks of MRSA are proof of the limitations of standard deep cleaning.

This technology cannot see around corners or into shaded areas. It will not disinfect the inner pages of magazines which are not exposed. Depending on room layout, it may need to be moved/ repositioned a number of times to get the best possible result. Stacking units can help increase coverage. Having said that, the approx. time for the size of room you mention with furniture, magazines etc using one unit is approx. 10 minutes.

UV-C is well proven in relation to MRSA and while COVID-19 is the ‘new kid on the block’, it is also well proven against close relatives of COVID-19 in recent years. The International Ultraviolet Association (IUVA) believes that UV disinfection technologies can play a role in a multiple barrier approach to reducing the transmission of the virus causing COVID-19, SARS-CoV-2, based on current disinfection data and empirical evidence. UV is a known disinfectant for air, water and surfaces that can help to mitigate the risk of acquiring an infection in contact with the COVID-19 virus when applied correctly. This product will address the need to sterilise rooms.
UV-C light has been used extensively for more than 40 years in disinfecting drinking water, waste water, air, pharmaceutical products, and surfaces against a whole suite of human pathogens (Fluence UV Dose Required review IUVA: https://www.iuvanews.com/stories/pdf/archives/180301_UVSensitivityReview_full.pdf ). All bacteria and viruses tested to date (many hundreds over the years, including other coronaviruses) respond to UV disinfection. Some organisms are more susceptible to UV-C disinfection than others, but all tested so far do respond at the appropriate doses.
COVID-19 infections can be caused by contact with contaminated surfaces and then touching facial areas (less common than person-to-person, but still an issue). Minimizing this risk is key because COVID-19 virus can live on plastic and steel surfaces for many hours. Normal cleaning and disinfection may leave behind some residual contamination, which UVC can treat suggesting that a multiple disinfectant approach is prudent. Accepting as mentioned above that where the UV-C light cannot reach a particular pathogen, that pathogen will not be disinfected. However in general, reducing the total number of pathogens reduces the risk of transmission. The total pathogenic load can be reduced substantially by applying UV to the many surfaces that are readily exposed, as a secondary barrier to cleaning.

Handheld, compact GUV products are sold but are considered a serious safety concern in a general household environment, where children, pets, or careless adults can easily be overexposed. These products are typically less than 10 watts, with open and exposed mercury lamps. They may come with a safety timer; a person places the open lamp on a table or in a convenient location, sets the timer for several minutes to an hour, and is given a 10-second delay to quickly exit the room and close the door.

UV rays in general will degrade paint, yellow plastics, and destroy air filters based on their composition (thus, UV-C irradiation of respirators for reuse should be only be a last resort in a pandemic).
Furthermore, shorter-wavelength UV photons have higher energy potential than longer-wavelength UV photons, and may have an accelerated aging effect on materials and paints. UV-C may damage plants; therefore, hanging plants should not be placed in the disinfection zone in upper-room applications or in whole-room UV-C applications.

Hospitals and healthcare facilities have rooms that can be closed off to individuals for a length of time. So-called “UV-C robots” have been used to move around a room to disinfect surfaces with UV-C in all directions. The UV-C radiant energy is normally emitted by long, vertical mercury lamps or pulsed xenon lamps. It is a challenge to estimate dose, but very intense emission can cover much of the room in a relatively short time. Further, by moving autonomously around the unoccupied work space it can expose surfaces that would not be easily reached by fixed GUV lamp installations. If good air movement is present, most air will be disinfected as well, and the dose requirements noted in the answer to the previous question could be applied. Surfaces with thick buildup of residues may pre-absorb the UV-C photons before they reach the active virus or bacterium. As with all GUV systems, they should be considered as an effective adjunct to standard infection control cleaning guidance. These mobile units should be used after terminal cleaning of patient rooms and bathrooms.

This unit can be used to disinfect stables…particularly useful at the high-end/ high value racehorse sector. Room UV Sterilizers reduces the risk of infection and stops the spread of animal sickness. Healthy horses are a result of good hygiene and good disinfection practices. As many animal pathogens are airborne, UVC Sterilization can provide a clean living environment for the horses you care for.