UV-C - TECNICAL DATA (1)
For many years, ultraviolet (UV) germicidal lamps have been used for disinfection of air and surfaces within hospitals, care homes, laboratories and many other organisations where hygiene and cleanliness are of utmost importance. UV lamps are a proven technology when it comes to reducing bacteria, viruses and other harmful microorganisms that pose a risk to human health.
In light of the current Coronavirus outbreak, UV is one of the many technologies available and being utilised to help reduce and control the spread and it has been valued as a performing one
see International UltraViolet Association (IUVA) article
and UV air and surface treatment
recommendation from The American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) What is UV?
Ultraviolet (UV) light is part of the electromagnetic spectrum. UV is further divided into three wavelength ranges:
UV-A (near UV) - from 315 nm to 400 nm
UV-B (middle UV) - from 280 nm to 315 nm
UV-C (far UV) - from 180 nm to 280 nm
VUV (vacuum UV) – from 10 to 180 nm
UV-A radiations are easily transmitted through air and glass; they penetrate through the epidermis and the anterior ocular media. (NEHC 1992
; Int. UV. Association FAQs
UV-B and UV-C are transmitted through air and quartz, but absorbed by ordinary glass. These wavelengths are also absorbed by the ozone layer of the upper atmosphere and generally do not reach the earth's surface. UV radiation below 315 nm is primarily absorbed by the cornea or by the top epithelial skin layer. (NEHC 1992
; Int. UV. Association FAQs
Radiations with wavelengths from 10 nm to 180 nm are sometimes referred to as "vacuum" or "extreme" UV. These wavelengths are not transmitted through air; thus, biological studies on this UV range are of little concern. (NEHC 1992
; Int. UV. Association FAQs
Among UV wavelength ranges, UV-C has the best potential ability to inactivate microorganisms because the wavelength 250-270 nm is strongly and mainly absorbed by the nucleic acids. (Yin 2013
UV-C lights germicidal function is largely due to the result of thymine dimers formation, which inactivate the microorganism's DNA or RNA, leaving them unable to perform vital cellular functions. (Chanprakon 2019
; Spencer 2017
; Gostine 2016
; Ultraviolet germicidal irradiation handbook 2010
; Cutler 2011
; CIE 2003
Most commercial UV-C lamps are low-pressure mercury lamps that emit UV energy at 253.7 nm, very close to the optimal wavelength. What are the beneficial uses of germicidal UV?
UV germicidal technology is a non-chemical approach to disinfection. In this method, no chemical agent is added to the space/room to be disinfected, which makes this process safe, simple, and inexpensive; moreover, it requires very low maintenance. UV sanitizers utilize germicidal lamps that are designed to give a certain dosage of UV radiation. The germicidal exposure dose is a function of the UV irradiance multiplied by the exposure time; you must have a certain amount of both for a successful design.
Here are just a few of the applications…
- Drinking Water
- Airstream disinfection
- Food Processing
- Medical (see Engmotion's application in automation for syringe filling machines or citostatics and antibiotics preparation machines)
_________________________________________________ Warnings in case of UVC light high exposure
UV-C radiation is a low-penetrating form of UV as compared to UV-A or UV-B radiation. Measurements on human tissue show that the amount of UV-C transmitted through the epidermis is minimal (Diffey 1983
; Bruls 1984
Nonetheless, UV-C radiation is invisible to humans and exposure to U-VC radiation may have an effect on health, in particular on eye and skin (International Organization for Standardization 2016
Currently available data do not allow to assess quantitative the risk of cancer associate to UV-C lamps exposure. The attenuation provided by the stratum corneum and epithelial tissues of the skin greatly should reduce carcinogenic risk; however, UV-C can be capable of inducing skin cancer in humans (SCHEER 2017
Precautions are recommended when using UV-C light devices. Warning signs should be placed in certain locations to protect personnel or passersby from UV hazards. Appropriate locations include access doors, air-handling unit outside walls, equipment room doors, etc.
The EU health agency's safety guidelines on the use of UVC- sources can be found here
Eye damage can result in photokeratitis and photokeratoconjunctivitis. Symptoms can include an abrupt sensation comparable to sand in eyes , tearing, and eye pain. Such symptoms may appear within 1-12 h after exposure and resolve fully within 24-48 h. Acute overexposure to UV-C radiation may cause incapacity due to eye discomfort, but this generally regresses after several days, leaving no permanent damage. Cutaneous damage consists of erythema, a reddening of the skin similar to sunburn. The maximum effect of erythema occurs at a wavelength of 297 nm (therefore, in the UV-B band). UV-C radiation at a wavelength of 254 nm is less effective in causing erythema (CIE 2010
, International Organization for Standardization 2016
) So are UVC devices safe?
Like any disinfection system, UV-C devices must be used in a proper way. Some devices also produce ozone as part of their cycle, others produce light and heat like an arc welder, others move during their cycles. Hence, general machine-human safety needs to be considered with all disinfection devices, and these considerations should be addressed in the operating manual, in the user training, and appropriate safety compliance.
The International Commission on Illumination (CIE) completed a review of UV-C photocarcinogenesis
risks from germicidal lamps. They concluded that overexposure to UV-C radiation include transient corneal and conjunctival irritation and skin irritation (erythema), disappearing within 24–48 hours. UV-C radiation is not currently known to produce lasting biological damage. The attenuation provided by the stratum corneum and epithelial tissues of the skin greatly should reduce carcinogenic risk; however, according to European Commission Scientific Committee on Health, Environmental and Emerging Risks, UV-C are capable
of inducing skin cancer in humans. Currently available data do not allow to assess quantitative the risk of cancer associate to UV-C lamps exposure. Ozone may also be produced from UV-C lamps emitting wavelengths shorter than 240 nm. Exposure to ozone, above threshold levels, presents a risk of a variety of symptoms and diseases associated with the respiratory tract, particularly in sensitive individuals
_________________________________________________________ UV-C Photodegradation of Materials
The UV-C energy used in HVAC applications can be detrimental to organic materials. If the UV is not applied properly and vulnerable materials are not shielded or substituted, substantial degradation can occur, resulting in decreased filtration efficiency, defective seals, and damaged system components, causing a possible loss in system performance and/or potential safety concerns (2016 ASHRAE Handbook
; Kauffman 2010
; NEHC 1992
The extent of material degradation caused by UV-C energy varies greatly with the material, UV intensity, length of exposure and design of the component. The effects of UV on materials are dose-dependent, as they are for microorganisms (Kowalski 2009
Short-term UVC exposures (1000–11000 μW/cm2
irradiance level range) were performed by Kauffman (Kauffman 2010
). Based on the relative degradation of the tested samples, the materials were ranked in four categories with respect to the UV-C resistance as follows:
(A) No effect (inorganic materials only; all organic materials exhibit some degradation)
(B) Minor effect (mainly cosmetic changes, not likely to affect materials ability to perform its duty)
(C) Moderate effect (some cracking/pitting suggesting protection/shielding should be considered)
(D) Severe effect (structural damage, not recommended)
Nevertheless, these damages were observed only after days or weeks of exposure at irradiances > 1000 μW/cm2
. For a lower irradiance range (50–1000 μW/cm2
) very long exposure time (months) are required to substantially damage materials (Wolf 2017
Some common polymers such as PE show signs of degradation at UV doses (10-100 J/cm2
) that are several hundred or even thousand time higher than that required to inactivate microorganisms (Kaczmarek 2006
With limited time applications such as the case of UV-C sanitizer robots, the material photodegradation is not that critical. It can effect only very thin materials.