Helping You Find Solutions
Helping You Find Solutions
Castine Bernardy, graduate research assistant, Department of Civil and Environmental Engineering, University of New Hampshire
Corresponding author James P. Malley Jr., Ph.D., Professor of Civil and Environmental Engineering, University of New Hampshire
Worldwide concern over the risk of contracting or spreading COVID-19 has sparked widespread interest in using UV devices for air and surface disinfection. The purpose of this Operator’s Corner is to provide tips to the buyers and users of UV devices to inactivate air and surfaces. That market contains thousands of different products and is estimated to be $1 to $2 billion per year in sales. Unfortunately, it lacks uniform validation protocols, manufacturing specifications or guidelines. Hence, it can be the “Wild West” so “Let the Buyer/User Beware.”
Ultraviolet (UV) means many things
Buyers and users need to familiarize themselves in some fashion with the different types of UV including UV-A (wavelength: 315 to 400 nm), UV-B (wavelength: 280 to 315 nm), UV-C (wavelength: 200 to 280 nm) and Vacuum UV (wavelength: 100 to 200 nm). The wavelength ranges given here are based upon IUPAC Gold Book-2020, and for the discussion of disinfection by these UV devices, UV-C wavelengths should be the focus. A subset of that UV-C, which has received some recent attention, is far UV-C (200 to 225 nm) and this, at times, is vaguely and incorrectly simply called far UV. In general, the lower the wavelength, the more energy in the photons of light wave energy being employed by the device.
When discussing the disinfecting power of sunlight, consider a mixture of approximately 95% UV-A and 5% UV-B. Given enough time (days) these wavelengths surely have many effects, but it is a long timeframe and many other factors come into play, such as desiccation of the organisms on a surface, etc.
There are many benefits to sunlight and fresh air, but sunlight is generally not considered as a practical disinfection option due to long timeframes.
All forms of UV have pros and cons, and careful consideration of which UV wavelengths are being used and for what purpose must be done. Dosing human and animal tissues with any forms of UV energy should not be done by buyers and users of these UV devices. Special cases performed by experienced medical professionals under very tightly controlled conditions for very specific medical problems may be found in internet searches, but “do not do this at home” is the best message for all buyers and users of UV devices.
Human and animal tissues should not come in contact with any forms of UV light unless it is performed by a medical facility under the careful control and monitoring by healthcare professionals. The UV devices sold to the public are not carefully regulated, and some advertisements make claims that are not supported by clinical medical trials and testing.
Time is not the most important factor
Often the information provided by advertisements and many very brief user manuals for UV devices simplify operations to talking about time.
All UV professionals recommend that UV device specifications be discussed in terms of delivered dose, since time is not the most important factor. The effectiveness of any UV device or application depends upon at least four key factors: a) the irradiance or fluence rate of the light source at specific wavelength(s) emitted (some refer to this as intensity or strength of light, but those are vague, non-technical terms), b) the optical geometry of the UV device or how it is to be applied, c) the type of organisms to be targeted, including such things as their action spectra and what amount of percent removal (or log inactivation) is desired and d) contact time. Of these lamp characteristics, optical geometry and organism characteristics are far more important than time.