What Is UV-C Radiation
What Is UV-C Radiation
1. UV radiation
UV-C is part of the electromagnetic spectrum that ranges from 100-400nm. Because of the different characteristics of the wavelength regions within the range of the ultraviolet radiation, a subdivision has been made in Vacuum UV (100-200nm), UV-C (200-280nm), UV-B (280-315nm) and UV-A ( 315-400nm). UV-C (254nm) is mainly used for disinfection. The disinfecting effect of UV-C radiation has been known for more than 100 years and is used worldwide in a wide variety of applications.
2. The disinfecting effect
UV-C has a disinfecting effect because it affects the DNA structures of micro-organisms. It causes a photochemical effect in thymines. These dimerise, which means that two adjacent information carriers are improperly linked. This molecular change makes the DNA unusable for the essential process of transcription (metabolism) and replication (cell division). As a result, the micro-organism is made harmless and dies.
3. UV-C lamps
The most efficient method to produce UV-C is in the low-pressure mercury vapor discharge lamp, in which an average of 35% of the energy is converted to UV-C. Lamps of good quality are made of a special form of glass that blocks ozone-forming radiation and have a minimal dose of mercury. Philips lamps are also equipped with a special coating that keeps the intensity of radiation at least at 80% of the initial intensity until the end of its life.
For the exposure to UV-C radiation regulations exist. The Commission of the European Community has created a proposal for a guideline. In this proposal, the Threshold Limit Values for UV radiation as defined by the American Conference of Governmental Industrial Hygienists (1993) was acquired. The TLVs applicable to exposure to UV-C radiation at 254 nm, are based on a value of 0,2 μWcm2 at a continuous exposure for 8 hours. The intensity of the radiation and the time of exposure together determine the dose. This means that variations in the intensity or exposure time interact inversely proportional. Overexposure to UV-C 254nm causes irritation of the skin (erythema) and eyes (conjunctivitis). These consequences can be painful but have no long term effect. The short-wave UV-C radiation, as opposed to UV with a longer wavelength, does not penetrate into the deeper layers of the skin or in the lens of the eye.
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.