The UV region of electromagnetic radiation extends from 200-400 nm and is divided into UVA. (320-400 nm), UVB (290-320 nm) and UVC (200-290 nm). Below 200 nm, the radiation is absorbed by air molecules; hence, it is called vacuum ultraviolet, as one needs to pull a vacuum to observe it. The ozone layer absorbs the UVC region of the Earth entirely and partially absorbs UVA and UVB. About 80% of UVA and 20% of UVB make it to the Earth's surface. Bacteria and viruses have not been exposed to natural UVC radiation; therefore, UVC can act as a germicidal radiation that disrupts their DNA and prevents them from multiplying.
It is well known that viruses are obligate parasites that attach to host cells and cannot multiply without the support of host cells (Reference 1). In any environment, different surfaces can become contaminated when body fluids infected with the virus come into contact with them, or when aerosol particles emitted through sneezing and coughing settle on them. The virus survives on the surface for a few hours until it finds a suitable host in the form of another person touching that surface, followed by touching the mouth, nose, or eyes. Recently, there have been a number of outbreaks due to viruses such as Hepatitis Virus, West Nile Virus, Enterovirus (Related to the intestines), Severe Acute Respiratory Syndrome (SARS), and, most recently, COVID-19, which has caused a worldwide pandemic. The most threatening viral emergence is enteric viruses and SARS, which have posed significant public health threats. The ability of these viruses to spread through close interpersonal contact and also through droplets when a person touches a contaminated surface with infected droplets and then touches his/her face makes them very dangerous.
Many measures can be taken to control the spread of viral diseases, such as SARS-CoV, which occurred in 2003, and SARS-CoV-2 (COVID-19), which is happening now, by disinfecting surfaces where these viruses reside. These measures could include heating the surface to sterilize it, using chemical disinfectants such as Lysol, and Ultraviolet Germicidal Irradiation (UVGI). However, the first two methods could potentially damage surfaces, as some surfaces cannot be sterilized by heat, and chemical solutions may also damage them. Unlike the first two methods, UVGI has proven to be an effective disinfection method that does not damage surfaces. The absorption peak of a DNA molecule is around 264 nm, and using a mercury lamp that emits at 253.7 nm generates dimers that can interfere with DNA replication and also destroy nucleic acids, effectively destroying viruses.
Viruses can be divided into four groups: single-stranded RNA (ssRNA), single-stranded DNA (ssDNA), double-stranded RNA (dsRNA), and double-stranded DNA (dsDNA). In one study, it was found that the double-strand versions of RNA and DNA are less sensitive to UV decontamination than the single-strand versions and require two to three times the UV irradiation to be deactivated. The radiation dose and humidity levels also played a part. To calculate the radiation dose, the irradiance at a given distance is multiplied by the exposure time in seconds, as shown below.
Dose UV (J/cm2) = Irradiance (W/cm2) * Temps (s)
It turns out that a dose of 2-5 mJ/cm 2 will reduce the virus population by 90% (Reference 1, Reference 4). For example, for a lamp with 200 mW/cm 2 irradiance at 10 ft, it will take 10 to 25 seconds to disinfect a surface 10 ft away. Increasing humidity will also reduce the effectiveness of UV disinfection, as the study found that at 85% humidity, it was harder to disinfect the surface than at 55%. This could be due to the absorption of UV radiation by the water covering the surface, reducing the dose that reaches the virus and deactivating it.
Aside from disinfecting surfaces, UV germicidal lamps have also been used to clean N95 masks and hospital equipment. Due to the current pandemic, there is a shortage of N95 masks, and one strategy is to reuse them by disinfecting them with UVGI.
Dans ce projet, deux puissants systèmes UVGI, chacun doté de huit lampes à mercure de 34 watts émettant à 254 nm, ont été placés aux sommets opposés d'un losange, distants de 2,4 mètres. Des fils ont été tirés sur la plus grande diagonale du losange, longue de 4 mètres, et des filtres N95 y ont été suspendus. Les unités devaient fournir 200 mW/cm² à une distance de 3 mètres. Un détecteur UV, illustré à droite de la figure, mesurait 400 mW/cm² pour les deux unités. Une dose de 800 à 1 200 mJ/cm², nécessitant 15 à 20 minutes d'irradiation, a suffi à désinfecter les masques avant leur réutilisation.
Outre les lampes à décharge telles que les lampes au mercure (254 nm) et les lampes au xénon pulsé (200-320 nm, UVC-UVB) à impulsions millisecondes, les panneaux DEL UV sont également utilisés pour la désinfection et l'élimination des bactéries et des virus. Des DEL UV à 266, 270, 275 et 279 nm ont été fabriquées et utilisées pour éliminer les bactéries dans les aliments (référence 5). Les DEL UV présentent quelques avantages par rapport aux lampes à décharge :
- La longueur d'onde n'est pas fixe (254 nm pour une lampe à mercure) et peut être personnalisée. Certaines longueurs d'onde, comme 260 nm, sont plus efficaces pour tuer les bactéries et les virus.
- Les lampes à décharge ont une faible activité dans les environnements réfrigérés
- Risque d'exposition au mercure
However, discharge lamps are generally more powerful and preferred for decontaminating a spacious hospital room.
Le rayonnement UVC est dangereux pour la peau et les yeux. Les locaux doivent être complètement évacués pendant les opérations de désinfection. Si les lampes UV sont utilisées par le personnel, celui-ci doit porter un équipement de protection individuelle (EPI) approprié pour protéger sa peau et ses yeux. Il pourrait être plus simple d'utiliser un robot pour déplacer la lampe UVC dans la pièce afin de désinfecter les surfaces et d'éviter tout danger pour les opérateurs humains.
Allied Scientific Pro has introduced a line of UVC germicidal lamps mounted on very useful robots.
References:
1 - Inactivation of viruses on surfaces by Ultraviolet Germicidal Irradiation, Chun-Chieh Tseng et.al, Journal of Occupational and Environmental Hygiene, 4, 2007.
2 - https://memoori.com/ can-uv-light -kill- coronavirus- in-our- contaminated-buildings/
3- Irradiation germicide ultraviolette des masques respiratoires filtrants N95 contaminés par la grippe,
Devin Mills et al., American Journal of infection control, 46 (2018)
4- Masque respiratoire filtrant N95 Procédé UVGI pour décontamination et réutilisation, médecine du Nebraska, 2020.
5- Utilisation de diodes électroluminescentes UVC à des longueurs d'onde de 266 à 279 nm pour inactiver les agents pathogènes d'origine alimentaire et le fromage en tranches pasteurisé, Soo-Ji Kim et.al, Applied and Environmental Microbiology, volume 82, numéro 1, 2016.