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. Germicidal lamps and ozone
) is a gas molecule that contains three oxygen atoms. Ozone is present in low concentrations throughout the earth's atmosphere. The ozone layer protects the Earth's stratosphere from the Sun's ultraviolet radiation, which could hinder the life on Earth. At sea level, however, a high concentration of ozone can be toxic to plants and animals. In humans ozone can induce adverse health effects in the respiratory tract (nose, throat and airways), in the lungs, and at higher concentrations, in the eyes.
UV light can react with oxygen and/or ozone molecules, depending on its wavelength:
- UV wavelengths < 240 nm generate ozone via photolysis of the oxygen molecule
- UV wavelengths between 240-315 nm destroy ozone via photolysis of the ozone molecule
A UV lamp emitting at 185 nm can generate ozone by splitting the oxygen (O2
) molecule into two oxygen atoms. These oxygen atoms can join other oxygen molecules, creating ozone. UV light in the 240-315 nm wavelength range will break this ozone molecule and convert it back to oxygen. Therefore, a UV-C lamp emitting at 253.7 nm wavelength can actually destroy ozone.
The tubes of most germicidal lamps are made of doped quartz glass, which blocks the transmission of the 185 nm line (ozone-producing wavelength) and allows the 253.7 nm radiation to pass through. Therefore, germicidal lamps with doped quartz tube cannot produce ozone. On the other hand, a pure quartz tube is transparent to all UV wavelengths and permits the radiation of the two UV-C peaks (254 nm and 185 nm) to be emitted. It is therefore possible to categories germicidal lamps into:
- ozone-free lamps, emitting at 254 nm only
- ozone-generating lamps, emitting at 254 nm and 185 nm
NASA Ozone Facts
UV-Resource: Why UV-C Cannot Produce Ozone Scientific Committee on Health, Environmental and Emerging Risks of European Commission
Oxidation Technologies LCC - Ozone production from UV What if a germicidal lamp breaks?
Low pressure mercury vapor lamps, often called "germicidal lamps", are a highly efficient electric discharge lamps in which UV light is emitted (predominantly at wavelengths of 253.7 and 185 nm ) by excited atoms of vaporized mercury (Scientific American, Working Knowledge: Compact Fluorescent Lightbulbs
; Lamptech, the Mercury Vapor Lamp
; Edison Tech Center, Mercury Vapor Lamps
); EnergyStar.gov, Learn about compact fluorescence bulbs
Mercury is a toxic heavy metal that can harm biological organisms if released. When a mercury-containing lamp (such as a germicidal lamp) breaks or explodes, mercury contamination can occur. Possible mercury contaminations have to be properly handled.
Mercury may have toxic effects on the nervous, digestive and immune systems, and on lungs, kidneys, skin and eyes. Mild, subclinical signs of central nervous system toxicity can be seen in workers exposed to an elemental mercury level in the air of 20 μg/m3
or more for several years (World Health Organization, Mercury and health
Germicidal lamps contain an average of 7.6 mg of mercury per lamp, with a high of 70 mg and a low of 5.5 mg (IMERC Fact Sheet - Mercury Use in Lighting
). According to another source
, germicidal lamps contain between 10 and 50 mg of mercury per lamp.
According to Environmental Defense Fund (see "Mercury Risk in CFLs: The Facts
"), the amount of mercury in a compact fluorescent light bulb (which use a technology very similar to that of germicidal lamps) is very small, almost one thousand times less than the amount of mercury found in old thermometers. Even if a bulb breaks, less than one milligram of mercury might become airborne in the room during the first eight hours, and only a fraction of that would be breathed in. Briefly, the exposure from breaking a mercury-containing bulb is in the same range as that deriving from eating a can of tuna fish. According to another study ("Release of Mercury From Broken Fluorescent Bulbs
"), between 17% and 40% of the mercury in broken fluorescent bulbs can be released to in a two-week period. In this case, 2-20 mg of mercury could be released from a broken germicidal lamp.
According to an E.U. Scientific Committee on Health and Environmental Risks opinion
, when a light bulb breaks, the amount of mercury vapor in an average room could briefly exceed the safety levels. However, these levels take into account adults who are regularly exposed to such quantities for 40-year work life, so they are not applicable to very short-term exposure. Most of the released vapor turns back to liquid form very quickly shortly after the breakage, therefore the level of mercury vapor becomes too low to cause any harm. According to an article
published in Environmental Health Perspectives, only a tiny fraction of the mercury is actually released when the bulb breaks. A study
in the Journal of Environmental Engineering Science reports that even if left unattended for 24 hours, a broken bulb will release from 0.04 to 0.7 milligrams of mercury. The researchers found that it would take weeks for the amount of mercury vapor in the room to reach hazardous levels. This can be avoided by quickly following a safe cleanup procedure.
For example, U.S. Environmental Protection Agency recommendation
for cleaning up
- Leave the room; air out the room for 5-10 minutes by opening a window or door to the outdoor environment; shut off the central forced air heating/air-conditioning system; collect materials needed to clean up broken bulb.
- Do not use a vacuum cleaner: vacuuming is not recommended, since it could spread mercury-containing powder or mercury vapor. Collect carefully broken glass and visible powder. Scoop up glass fragments and powder using stiff paper or cardboard. Use sticky tape to pick up any remaining small glass fragments and powder. Place cleanup materials in a sealable container.
A similar procedure is described in the "Cleaning Up a Broken Lamp" section of the "Safety Tips for Using Germicidal Lamps
(2017) from Lawrence Berkeley National Laboratory.
Other similar cleaning procedure: OSRAM –handling broken lamps
North Carolina Public Health Service document
concerning mercury-containing lamp bulbs
Lighting Europe 2020 - Frequently Asked Questions
on mercury related regulations for light sources
National Geographic – Myths and Facts
on fluorescent light bulbs
Scientific American - Are Compact Fluorescent Lightbulbs Dangerous?
Lamprecycle.org – Broken Bulbs
Lamprecycle.org – Dangerous mercury in compact fluorescent lights?
E.U. Scientific Committee on Health, Environm. and Emerging Risks - Opinion on mercury inside light bulbs