Sparks Electrical News May 2020

LIGHTING

18

UV Disinfection U ltraviolet (UV) light is a form of radiation that is invisible to the human eye and occupies the portion of the electromagnetic spectrum be- tween X-rays and visible light. UV radiation is produced by the sun and man-made sources. The International Commission on Illumination (CIE), classifies UV radia- tion as follows: UV-A, 315 nm– 400 nm; UV-B, 280 nm – 315 nm; UV-C, 100 nm – 280 nm. The CIE’s activities include the development of international measurement standards and procedures in the field of light, including ultraviolet radiation. The National Metrology Institute of South Africa (NMISA) Photometry & Radiometry (P&R) section is affiliated to the CIE via the Illumination Engi- neering Society of South Africa (IESSA) and has inter- national representatives on the different divisions within the CIE. CIE Division 6: Photobiology and Photochemis- try has specific research activities in the field of germi- cidal irradiation. The energy of a UV photon is wavelength de- pendent: shorter wavelength photons (i.e. UV-C) have higher energy than longer wavelength pho- tons. It is well-known that UV radiation interacts with living cells. Most of the UV from the sun is in the UV-A region, which penetrates deeply into the skin and causes most of skin ageing. Next there is UV- B, which causes sunburn and ultimately skin can- cer. Both UV-A and UV-B can be blocked by a good sunscreen. The sun also emits shorter-wavelength UV-C which is more energetic and more dangerous, but which fortunately gets completely filtered out of solar radiation by ozone, water vapour, oxygen and CO 2 in the atmosphere. Photobiological interaction In 1878, Arthur Downes and Thomas P. Blunt published a paper describing the sterilisation of bacteria exposed to short-wavelength light, and the 1903 Nobel Prize for Medicine was awarded to Niels Finsen for his use of UV against tuberculosis of the skin. Wavelengths between about 200 nm and 300 nm are strongly absorbed by nucleic acids, which can destroy the molecular bonds and result in defects of an organism’s DNA and RNA, and thereby prevent replication of genetic material or the expression of necessary proteins, resulting in the death or inactivation of the organism. Some micro- organisms, particularly bacteria, have a photorepair mechanism which uses visible and UV-A radiation to repair the chemical bonds damaged by UV-C, so care must be taken to keep these levels low. Uses Artificially produced UV-C is used in Ultraviolet germi- cidal irradiation (UVGI) and has been a staple method of sterilization against pathogens for over 60 years. UV-C light has been demonstrated to be effective against pathogenic organisms, including those respon- sible for cholera, polio, typhoid, hepatitis and other bac- terial, viral and parasitic diseases. The degree of sterilization by UVGI is directly re- lated to the UV dose. The dosage, a product of UV light irradiance (radiant power per area) incident on a surface and exposure time, is usually meas- ured in microjoules per square centimetre (μJ/cm 2 ), or equivalently as microwatt seconds per square centimetre (μW·s/cm2). Determining the dosage requires that the integrated spectral irradiance of such a source is calibrated using suitable radiomet- ric standards. Dosages for a 90% kill of most bac- teria and viruses range from 2 000 μW·s/cm 2 to 8 000 μW·s/cm 2 . UVGI is routinely used in medical sanitation to de- contaminate surgical surfaces and equipment, and modern applications have autonomous robots and drones covering a predetermined path in unoccu- pied areas, leaving them sterilized for use. UV-C lamps can be used to sterilize the air in ar- eas where illnesses like tuberculosis can pass from person to person in droplets ejected by coughing or sneezing. UVGI units are typically mounted on walls and irradiate the upper region of a room where they inactivate viruses and bacteria which circulate on air currents. UV-C is used as an environmentally friendly, chemical-free, and highly effective way to disinfect and safeguard water against harmful microorgan-

isms, including some parasites which are resistant to chemical disinfectants such as chlorine. UV-C is also used by blood transfusion services to irradiate blood. Here the dose is critical as too high a dose can potentially have a negative impact. Hazards In humans, skin exposure to UV in general can result in skin irritation (sunburn and in some cases skin cancer), and exposure of the eyes to UV-C can produce an ex- tremely painful inflammation of the conjunctiva (pho- toconjuntivitis) and of the cornea (photokeratitis), but usually disappears within 48 hours without permanent damage. Temporary or permanent vision impairment, up to and including blindness can occur in some cases due to cataracts caused by UV-B. Under extreme over- exposure UV-A can also damage the retina of the eye (photoretinitis). UVGI in occupied rooms should not exceed an exposure dose of 6 mJ/cm² per eight hours for low-pressure mercury lamps. Designers and users should also be aware of high UV intensities being re- flected from certain materials, for example the reflec- tors of open luminaires, windows, exposed ducting and metallic or high gloss architectural finishes, into the oc- cupied portion of the room. During any work with open UVGI devices, eye and skin protection should be worn. To use UV-C safely, specialist equipment and training is necessary. The World Health Organization (WHO) has issued a stern warning against using UV light to steri- lise their hands or any other part of their skin. Another potential danger is the UV production of ozone. UV-C light from the sun is partly responsible for the earth’s ozone layer in the stratosphere, but ozone at the atmospheric level can be harmful to a person’s health. This risk is mitigated using ozone-free lamps which are made of glass or fused quartz which is doped to block ozone-producing UV radiation. UV-C radiation can break chemical bonds, which leads to rapid ageing of plastics and other materials. Note that plastics sold as ‘UV-resistant’ are tested only for UV-B, as UV-C doesn’t normally reach the surface of the Earth. Lamps Germicidal UV-C for disinfection is typically generated by a mercury-vapor discharge lamp. Mercury vapor lamps may be categorized as either low-pressure or medium-pressure mercury lamps. Low-pressure mer- cury lamps have a strong emission line at 254 nm, which is close to 265 nm where the germicidal ef- fectiveness peaks and therefore offer high conversion efficacy (ratio of germicidal radiation output to power input) but lower power density (power per unit length) and have a bulb temperature of about 30°C. Medi- um-pressure mercury lamps operate at much higher temperatures, up to about 800°C, and offer higher ra- diation output and power density but lower conversion efficacy compared to low-pressure mercury lamps due to the fact that only 10-15% of the radiant output is in the UV-C. Recent developments in LED technology have led to commercially available UV-C LEDs. UV-C LEDs use semiconductors to emit light between 255 nm and 280 nm. The wavelength emission can be tuned by adjusting the material of the semiconductor. The electrical-to-UV-C conversion efficiency of LEDs is however lower than that of mercury lamps. Use of UV-C in South Africa and worldwide South Africa is one of the countries with the highest burden of tuberculosis (TB), a disease spread by air- borne aerosols which poses a threat to people in a contaminated area. The problem is exacerbated by the emergence of drug-resistant strains and HIV/AIDs. The disinfection effectivity of UVGI and the suscepti- bility of airborne microorganisms including M. tuber- culosis (TB) bacilli (peak sensitivity at around 265nm) have been scientifically proven, and the World Health Organization (WHO) policy on TB infection control recommends defined ventilation rates supplemented by Ultraviolet Germicidal Irradiance (UVGI). The output of the devices which produce UV-C for UVGI must be carefully characterised to ensure that an effective level of UV-C is emitted in the desired zone (typically the upper region of a room), while ensuring that the levels

of the entire spectrum of light (from UV to infrared) in the occupied region of the room remains below a safe level. This characterisation requires that the spectral ir- radiance of such lamp is calibrated against calibrated standards. Although there hasn’t yet been any research look- ing at how UV-C affects the COVID-19 virus specifi- cally, studies have shown that it can be used against other coronaviruses, such as SARS. Here too, the UV-C radiation warps the structure of the genetic material and prevents the viral particles from mak- ing more copies of themselves. As a result, UV-C is now a useful weapon in the fight against COVID-19. In China, whole buses are being irradiated each night, and UVC-emitting robots have been cleaning floors in hospitals. Banks have even been using the light to disinfect their money. UVGI has been shown to be an effective sterilization method for N95 filter- ing masks, which could become necessary with the current shortage. The Photometry and Radiometry section of NMI- SA has an accredited UV laboratory which is man- dated to continuously develop and maintain accu- rate and traceable national measurement standards, and which has extensive and unique experience in the measurement and characterisation of UV-A, UV-B and UV-C sources and detectors. It maintains international equivalence through participation in International Key Comparisons, participating in sci- entific committees and active involvement in inter- national workshops and conferences. The UV Laboratory of NMISA’s P&R section fre- quently calibrates broadband UV radiometers that are used to measure the effective UV irradiance pro- duced by a UV source. The accurate use of these radiometers requires an understanding of the prop- erties of the UV source and radiometer, as well as the measurement and calibration methods involved. The calibration of a UV radiometer depends on the source used during calibration, the properties (es- pecially spectral) of the radiometer and on the ef- fect to be measured. For the calibration of a UVGI radiometer the effective germicidal action is also important. If the calibration is not performed using the same source as the source to be measured in the field, very large errors can occur. It is therefore critical that the calibration of the UV radiometer is fit for purpose. This UV laboratory is currently undergoing up- grades to improve on its current capabilities. This includes a new automated three-axis calibration workstation capable of performing calibration and characterisation of UV radiometers, including UV-C, UVGI and UV hazard radiometers. Further upgrades underway in the NMISA P&R Spectroradiometry and Radiometry laboratories will also mean that the spectral characteristics of UV sources and radiom- eters can be determined with improved accuracy in South Africa. Lookout for an article on ‘The ultraviolet meas- urement capabilities at NMISA’ in the next issue of Sparks Electrical News magazine. By Liesl Burger, Pieter du Toit and Rheinhardt Sieber- hagen, Photometry and Radiometry Section, National Metrology Institute of South Africa (NMISA)

REFERENCES: 1. CIE 155:2003 Ultraviolet air disinfection, 2003 2. ISO/CIE 28077:2016 Photocarcinogenesis action spectrum (non-melanoma skin cancers), 2016 3. CIE 187:2010 UV-C Photocarcinogenesis risks from germicidal lamps, 2010 4. ISO/CIE 17166:2019 Erythema reference action spectrum and standard erythema dose, 2019 5. CIE 220:2016 Characterization and calibration methods of UV radiometers, 2016 6. Can you kill coronavirus with UV light? (www.bbc. com/future/article/20200327-can-you-kill-corona- virus-with-uv-light), 2020 7. Effectiveness of an ultraviolet-C disinfection system for reduction of healthcare-associated pathogens, Jui-Hsuan Yanga, Un-In Wu, Huei-Min Tai, Wang-Huei Sheng (www.sciencedirect.com/science/article/pii/ S1684118217302001), 2019 8. The effectiveness of UV-C radiation for facility-wide environmental disinfection to reduce health care– acquired infections, Nathanael A. Napolitano, Tanmay Mahapatra, Weiming Tang (www.sciencedirect.com/ science/article/abs/pii/S0196655315007579), 2015 9. Wikipedia - Ultraviolet germicidal irradiation (en. wikipedia.org/wiki/Ultraviolet_germicidal_irradiation) 10. Ultraviolet Germicidal Irradiation Handbook - UVGI for Air and Surface Disinfection, Wladyslaw Kowalski (link.springer.com/book/10.1007/978-3-642- 01999-9), 2009 11. UV Sterilization: Far-UVC light kills airborne flu viruses without danger to humans, John Wallace (1 April 2018) (www.laserfocusworld.com/lasers- sources/article/16555364/uv-sterilization-faruvc- light-kills-airborne-flu-viruses-without-danger-to- humans), 2018 12. Ultraviolet germicidal irradiation of influenza- contaminated N95 filtering facepiece respirators, Mills D, Harnish D.A., Lawrence C., Sandoval-Powers M., Heimbuch B.K. (www.ncbi.nlm.nih.gov/pub- med/29678452), 2018 13. N95 Filtering Facepiece Respirator Ultraviolet Ger- micidal Irradiation (UVGI) Process for decontamina- tion and reuse, Lowe J. L., et al (www.nebraskamed. com/sites/default/files/documents/covid-19/n- 95-decon-process.pdf), 2020 14. Ultraviolet germicidal irradiation (web.archive.org/ web/20160806185506/https://www.liverpool.ac.uk/ media/livacuk/radiation/pdf/UV_germicidal.pdf), 2016 15. Predicted Inactivation of Viruses of Relevance to Biodefense by Solar Radiation, David Lytle and Jose- Luis Sagripanti (www.ncbi.nlm.nih.gov/pmc/articles/ PMC1280232/), 2005 16. IUVA Fact Sheet on UV Disinfection for COVID-19 (www.iuva.org/COVID-19) 17. Using Light to Fight Bacteria and Viruses, Roger Pink (electronics360.globalspec.com/article/12151/using- light-to-fight-bacteria-and-viruses), 2018 18. Coronavirus disease (COVID-19) advice for the public: Myth busters (www.who.int/emergencies/ diseases/novel-coronavirus-2019/advice-for-public/ myth-busters) 19. Efficacy assessment of ultraviolet germicidal ir- radiation (UVGI) devices for inactivating airborne Mycobacterium tuberculosis, T Singh, Ngcobo, O Kgasha, W Leuschner, O Matuka, T van Reenen, P de Jager (Occupational Health Southern Africa 24, 4, August 2018

Enquiries: www.nmisa.org and www.iessa.org.za

SPARKS ELECTRICAL NEWS

MAY 2020