Disinfecting with GUV Simplified: Focus on Dosage, Duration, and Danger
January 14, 2021 Author: David P. Drumel, P.E. Images courtesy of IES.
There has been a substantial level of excitement in the industry and in the news about the potential of GUV (Germicidal Ultra-Violet) to help in the fight against Coronavirus. The concept isn’t new; it has been in use for 75 years for Tuberculosis and other viruses and is proven to work. Really, it would be more correct to say that it has never been proven not to work on any virus, microbe, fungus, or spore, which means the solutions we put in place now should help on future outbreaks that are unfortunately likely to follow. But for those of us looking for actual products to specify, there seems to be a wild (or even wild west) variety of expensive options with misleading claims of performance and a lack of standards to measure them against. This leaves specifiers having to make more product evaluations on their own to ensure that the products and solutions they select are performers, not pacifiers. The key? Focus on Dosage, Duration, and Danger.
This is not as simple as it sounds; technically my failures in golf can also be broken down to just distance and direction but knowing that hasn’t made me any better at the sport. However, a focus on Dosage, Duration, and Danger when evaluating potential GUV solutions and products can provide some clarity.
Evaluating the Solutions
There is no single solution or approach that can be applied to every space type, but the three main GUV implementation approaches are:
1. Upper-room GUV Systems to reduce airborne transmissions in occupied spaces.
These systems are recommended for spaces with minimum 10’-0” ceiling height. UV-C fixtures mounted at 7’ or higher will efficiently disinfect the air above. Low velocity fans in the room ensure air is quickly cycled into the upper space for disinfection.
Dosage: Can be very high. Lamps must be mounted where no direct line of sight is possible for anyone in the space.
Duration: Lamp is on continuously and has sustained exposure to the airborne viruses.
Danger: When installed properly with no direct line of sight to the lamps, there is no danger, and the space can remain occupied.
This solution gets a very high total score as dosage, duration, and danger level are all excellent.
2. GUV in HVAC Air Handling Units to treat recirculated air and reduce mold growth.
Dosage: The UV source can operate continuously, but more lamps are needed to achieve the desired results as the large volume of air passes by.
Duration: The air is passing through the disinfecting zone at a high rate of speed, limiting the amount of time the UV source can act on the virus.
Danger: Safety measures must be implemented to ensure technicians servicing the HVAC unit are not exposed.
This solution gets a good score, but it is not as efficient, effective, or safe as upper-room disinfection. It is somewhat effective in ensuring that contaminated air does not re-enter a space or circulate into other areas but is not effective in preventing occupant-to-occupant transmission in shared spaces.
Dosage, Duration, and Danger: A simple rule to remember is that if it is dangerous to a virus, it is dangerous to a person. Mobile/portable GUV units (high dosage, short duration required) can be very effective in disinfecting surfaces, but great care must be taken not to expose people. Hand-held GUV wands are usually either underpowered and not dangerous or are functional but can easily be mis-used causing accidental exposure to the operator and surrounding occupants.
While this solution can certainly be effective under the right conditions, it also increases the risk of accidental exposure and should be carefully selected and applied by qualified personnel.
The same questions on Dosage, Duration, and Danger can be applied to the products as well.
Dosage: What is the power output? What light wavelength does the fixture produce? One of the keys to the effectiveness of a GUV product is the wavelength of the light that is emitted. Past products often used Mercury lamps which emit a highly effective 254nm wavelength, but there are a number of new products appearing on the market today using other sources and producing wavelengths well outside the ideal 200-280 band. To be effective outside of that band will require a substantial increase in power or duration.
Key Point: Look for products that operate in the 200-280nm wavelength.
Beware of: Products that don’t disclose the wavelength, source type, or output as well as those that operate at a wavelength that makes their usefulness questionable.
Duration: How long will the dosage be applied to the air or surface you are trying to disinfect? How fast do you need it to act? A source with a low score on dosage (low output and/or ineffective wavelength) will need a substantial duration to be effective. In some cases, the virus may not survive long enough on a surface for UV-C radiation to be relevant.
Key Point: Look for products that are designed to expose the UV light to the air or surface to be cleaned as quickly as possible after contact and for a sufficient amount of time to complete the disinfection.
Beware of: Products that don’t expose the source to the virus for a sufficient amount of time or require durations that are longer than the virus would survive in the environment anyway.
Danger: Can the source be seen? Will people or pets be exposed to it? Despite claims made by some manufacturers, most researchers believe direct exposure to any portion of the UV-C spectrum can be dangerous to humans, animals, and plant-life and should be avoided. UV-C can also damage or destroy organic materials like fabrics and plastics. Personnel should always wear proper personal protective equipment (PPE) when operating exposed GUV emitters that require the operator to be present during disinfection.
Key point: If it is dangerous to a virus, it is dangerous to a person. Far-UVC has potential to break this barrier, but more research is needed before specifying these products.
Beware of: Manufacturers that do not install safeguards, offer training, or require PPE use when direct exposure to their light source is possible.
Specifiers applying the tests of Dosage, Duration, and Danger can make good decisions about the new GUV products in the marketplace today and provide real solutions that will help in the fight against Coronavirus and whatever comes next. But remember the rule you were taught as a child still exists: If it sounds too good to be true, it probably is!
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