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Can UVC lamps inactivate the SARS-CoV-2 coronavirus?

Posted by June Lai on

Can UVC lamps inactivate the SARS-CoV-2 coronavirus?

During the Coronavirus pandemic, there have been many questions about UVC sanitizing devices, (a.k.a. ultraviolet-C (UVC) lamps) to disinfect surfaces versus using bleach or disinfectants to clean everything. This is probably because it seems lamps would be a little easier to work with when you have parts that can’t be doused with liquids, like bleach.

However, most consumers aren’t aware devices may not work or be safe to use when they’re disinfected to prevent the spread of COVID-19.

There's a huge need for COVID-19 education, but there's a gap in credible sources. We committed to spending the time and effort educating consumers on the fast-evolving world related to viruses and disinfection.

Firstly, what is UVC light? 

UVC is the radiation from the highest energy portion of the UV spectrum (100-280 nm)1.

Basically, it comes naturally from the sun, filtered by the ozone layer; but, it can also be created by artificial sources used in industry, commerce and recreation2.

UVC radiation has been employed to disinfect things such as:

  • drinking water
  • air
  • titanium implants
  • contact lenses, among other things3.

For this reason, UVC lamps are often called "germicidal" lamps, meaning that it kills germs. The range of 200–270 nm is known as the “germicidal UVC spectrum”4, because it is strongly absorbed by the nucleic acids and disrupting the DNA of a microorganism; and, therefore, is the most

How does UVC destroy germs?

UVC is electromagnetic radiation that works to inactivate germs and microorganisms, such as bacteria, viruses, yeast, molds, or protozoa. It does this by damaging their genomic material (their DNA or RNA).

Specifically, in viruses, viral inactivation works by altering the surface chemistry of a virus, making it unable to infect new cells. Many viruses contain lipid or protein coats that can be inactivated by chemical alteration, heat processing, solvents, etc.

UVC inactivation of viruses works by destroying the outer protein coating. This further damages the genetic material in the nucleus of the cell, or nucleic acids in the virus, which damages the DNA of the microorganism6,7.This makes the virus unable to replicate itself and infect new host cells, effectively killing the virus’ ability to spread.

UVC radiation has several potential applications, but unfortunately its effectiveness against germs is influenced by many factors like:

  • organic matter e.g. blood, body fluids, tissue
  • type of suspension, surface (e.g. porous or non-porous, flat or curved)
  • temperature
  • type of microorganism
  • UV intensity, which is affected by distance and dirty tubes and output3.

Currently, UV-C lamps are becoming more popular than ever, however it is critical to understand if they actually eliminate the virus that causes COVID-19.

Can UVC be used to disinfect against COVID-19?

According to the FDA, we don’t know; we don’t have enough information about the conditions needed for UVC to be used against COVID-19. There is very limited data published about the correct wavelength, dose, and duration of UVC radiation that would inactivate the SARS-CoV-2 virus from surfaces and equipment2.

There is some data that indicates that Far-UVC (222nm) may be effective. In a study on 2 different similar coronaviruses, Far-UVC light at the specific wavelength of 222nm was shown to destroy the outer protein coating of these human coronaviruses (alpha HCoV-229E and beta HCoV-OC43), ultimately leading to inactivation of the virus. 

Far UV-C radiation (222 nm) may also be effective in inactivating the SARS-CoV-2 virus (the human beta HCoV-OC43 comes from a similar family of coronaviruses as SARS-CoV-2), although these results are still preliminary8.

However, there are a lot of caveats. Even if these UVC devices do work, you may have a false sense of safety since you need to meet all of the conditions for the device to be effective, and not all of the virus on a surface may be killed.

The problem is that in order for UVC light to work, you need to directly expose the virus on all surfaces and all angles. That means that the UVC device needs to have a direct line of sight to the virus. For it to work correctly, the virus cannot be covered by dust or soil, contaminants such as bodily fluids, or embedded in porous surface or on the underside of a surface. 

Is it safe to use UVC lamps?

No. In general, direct exposure to UVC light is not proven to be safe and further studies are needed. According to the FDA, UVC lamps that are used for disinfection purposes may pose health and safety risks to you, depending on the UVC wavelength, dose, and duration when you are directly exposed to radiation from the device.

Depending upon the wavelength, direct exposure to UVC light is known to cause skin cancer or eye damage. UVC light can severely damage the human eye (photokeratitis), even causing a burning eye sensation9. UVC light can cause a stark, sunburn-like reaction to the human skin, with DNA mutations that can lead to cancer11 .

You should never look directly at a UVC lamp source, even briefly, due to the damage it may cause to your eyes. When around these devices, wear protective eyewear or a face shield, and fully cover up with clothing to avoid any exposure of your skin to the device2.

There are other significant safety risks. Ozone (O3) can be produced unintentionally in the air upon exposure to UVC rays, particularly with low-pressure Mercury (Hg) vapor lamps that can emit Vacuum-Ultraviolet (VUV) light at 185 nm10 12 . Ozone is a known human toxin. When inhaled even in relatively low amounts, it can damage the lungs, cause chest pain, coughing, shortness of breath and throat irritation.13

Ozone generation should be evaluated to ensure it is below the maximum acceptable level of ozone established by the FDA in 21 CFR 801.415.14 This states a device will not generate ozone at a level of .05 PPM by volume of air circulating through the device, or cause an accumulation of ozone in excess of .05 PPM by the volume of air in the atmosphere of the enclosed space. According to OSHA, the current NIOSH limit of ozone exposure for an 8-hour day of industrial workers, is .1 PPM15 .

The most common UVC lamps are made with mercury. Since mercury is toxic even in small amounts, you need to be very careful if you break the lamp and follow recommended safety guidelines from the manufacturer to clean and dispose of the lamp. The EPA provides instructions on how to safely clean up a broken lamp that contains mercury. These steps include leaving the room since mercury vapor may be released and not using a vacuum, which could otherwise spread mercury-containing powder or mercury vapor in broken parts.16

What are the different types of lamps that can produce UVC radiation?

Not all UVC lamps are the same, which complicates the conversation about whether or not UVC lamps work or are safe.

Lamps may emit very specific UVC wavelengths (like 254 nm or 222 nm), or they may emit a broad range of UV wavelengths. The wavelengths emitted by the lamp may affect the lamp’s ability to inactivate a virus. Some lamps emit multiple types of wavelengths including IR and visible light. Testing of the lamp can determine whetherit puts other wavelengths, and if so, how much. Some of these other wavelengths can also be a health hazard, both to the skin and eye.

The most commonly used UV lamp is a low pressure mercury-vapor arc lamp, which mainly (>90%) emits around 254 nm and also emits at other wavelengths. There are other lamps available that emit a broad range of UV wavelengths, but they also emit visible and infrared radiation, which can cause eye damage.

More recently, pulsed xenon lamps have been used in hospital operating rooms to disinfect surfaces when people are not present. These lamps emit a short pulse of broad spectrum (including UV, visible and infrared) light, filtered to emit mainly UVC radiation.

Light-emitting diodes (LEDs) that produce UV radiation are also becoming more commonly available, but there are a lot of questions about whether or not these work (see section on how reliable UVC lamps are below). Typically, these LEDs emit a very narrow wavelength band 

of radiation, usually with peak wavelengths at 214 nm, 265 nm, and 273 nm. While it is a good that they contain no mercury, the small surface area and higher directionality of LEDs may make them less effective for germicidal applications.

Lastly, there is some evidence that Excimer lamps (or Far-UVC lamps) that operate in the Far UVC light spectrum (207 to 22nm) with peak wavelength of 222-nm, may cause less damage to the skin, eyes, and DNA than the 254 nm wavelength, but long-term safety data is lacking. These excimer lamps contain argon-fluorine, krypton-bromine, or krypton-chlorine mixtures, which product Far-UVC light at 193, 207 and 222nm respectively.17, 18

At this time, these excimer lamps are mostly being used for evalutaion in labs, but are not the most commonly available UVC lamps in the marketplace, and there is very little experience with any widespread use.19 A major safety concern when considering excimer lamps for consumer use is UV sources emitting < 240 nm light can produce ozone. This is hazardous to human health, and would require sufficient ventilation to reduce the concentration of ozone.

How long do I need to use the UVC device for it to be effective?

It depends upon the wavelength and the dosage (output of the device). Many UVC lamps sold for home use are designed to provide a low dose. Even if the dosage is sufficient, it may take a lot longer exposure time to a given surface area to potentially inactivate a bacteria or virus.

So, the wavelength has a direct impact on safety and effectiveness, the dosage needs to be strong enough to work, and the lamp needs sufficient output to meet the dosage requirement.  The amount of UVC energy needed to effectively sanitize is much higher than normal sunlight10, which carries risks to humans if the device is not installed properly, or used by untrained individuals2.

There is a regulatory limit for the amount of 222 nm light the public can be exposed to, which is 23 mJ/cm2 per 8-hour exposure36,37. Based on test results on the beta HCoV-OC43 human coronavirus, continuous Far-UVC exposure at the regulatory limit would result in:

  • 90% viral inactivation in approximately 8 minutes
  • 95% viral inactivation in approximately 11 minutes
  • 99% inactivation in approximately 16 minutes
  • 9% inactivation in approximately 25 minutes.

How reliable is this method of disinfection?

It depends upon the conditions. The application of UV radiation in the health care environment (i.e., operating rooms, isolation rooms, and biologic safety cabinets) is limited to the destruction of airborne organisms or inactivation of microorganisms on exposed surfaces3. In other words, the virus or bacterium will not be inactivated if it is covered by dust or soil, embedded in porous shell, or on the underside of a surface2.

Even if scientific studies were done to establish the wavelength, dosage and duration to effectively disinfect against COVID-19, you would need to make sure the UVC lamp produces a high enough UVC output in order for the dosage to be effective. For UVC light to quickly inactivate in a short duration of time most germs (bacteria, viruses, yeast, molds, protozoa), you would need a high energy dosage of UVC to achieve a high kill factor (effectively inactivating most of the germs on a surface)20:

UVC lamps usually carry power ratings based on their power consumption rather than their power output. UV-C irradiance should not be calculated from rated lamp power, as bulbs do not have 100% efficiency in converting electrical energy to optical power. To determine the output, you would need measure irradiance using a UVC specific at the surface to measure the dose from lamp power. A rule of thumb for the most common mercury UVC lamp is that their actual 254nm output is between 10 and 30% of their input rating because of heat losses and the inefficiency of the lamp ballast. There are better quality, larger, high-power lamps but they cost more.21

Quality is important because it is possible to find inexpensive UVC lamps from China sold online whose quality is questionable. Many of these are advertised as being in the 10-W range. Experts say that for a 10-W lamp, a good ballpark output would be 1 W, so the output would actually only be 10% of the power rating.

What can we learn from research on UVC use to decontaminate and reuse masks?

Even in the scientific community, it has been important to validate each UV device manufacturer, as not all UV sources provide the required UVC wavelength range, irradiance, or irradiance uniformity. According to N95Decon.org (a consortium of scientists that have studied using UVC to support essential workers fighting COVID-19 by sharing scientifically-based information on the proper use of respirators, masks, and other personal protective equipment) viral inactivation protocols using UVC designed for surfaces or air are insufficient/not effective to decontaminate N95 masks for re-use22.

Testing of UVC sources used in research laboratories to disinfect and reuse masks (e.g., biosafety cabinets) found unacceptable non-uniformity and low power. The exact UVC dose on the N95 surface needs to be studied to understand conditions needed for that device to sufficiently decontaminate against COVID-19.

The consortium recommends using a substantially higher UV-C dose of 1.0 J/cm at the N95 surface for UVC light to be effective. The shape of the item being disinfected also impacts the dosage of UVC light received from a lamp depending upon the distance and angle of exposure to a surface. 23 UVC exposure needs to be irradiated on multiple sides/angles with no obstructions or materials blocking line-of-sight. This includes things such as cosmetics and sunscreen (which may block UVC) in order for all surfaces need to be exposed to the marginally acceptable UVC dose, and the CDC does not recommend wearing makeup or sunscreen with masks. The efficacy of UVC on different materials is different even on masks made of different materials, with incomplete decontamination on some materials requiring a second disinfection method (such as the elastic straps of facepieces) and other materials reflect light and thereby amplify dosage, and that at too high a dosage, some materials would be damaged. High humidity decreased effectiveness of UVC and soiling agents (dirt, makeup, sunscreen) also could reduce the effectiveness of UVC.

The consortium also found that many consumer UV products do not emit UV-C with sufficient irradiance, and have peak emission in the UV-A range (e.g., nail polish curing lamps, tanning bed lamps, etc.), which is ineffective for decontamination.

Are there other considerations that affect UVC devices?

The design (or form factor) of the device also has an impact on output. A typical 10-W lamp is about 8-in long, but the light-emitting part of the tube is only about 5-in long.

Lamps typically must warm-up before reaching full output. For some lamps, the process of turning the lamps on and off can diminish their lifespan and some manufacturers say that cycling the device on and off more than four times daily can diminish the life of the UVC bulb.

Most commonly available UVC lamps are made of mercury and produce UVC at 256nm at lower dosage output, however UVC light at this wavelength causes DNA mutations in cells. While Far UVC light (222nm) is less common, and while it is less likely to cause damage to skin or eyes, ozone forms at wavelengths below 242 nm and this creates additional safety concerns especially for use by consumers.

Beware of low cost UVC lamps. There are cost differences between mercury vapor UVC lamps and LED UVC lamps. For the same output level, LED UVC lamps are more expensive than ordinary LEDs. Unlike mercury vapor UVC lamps, high powered LEDs would likely require an additional heat sink, which also adds to cost. There have been reports that a lot of the germicidal lights based on LEDs are actually fake, putting out light in some other wavelength range other than UVC or that their UVC output is so low that the UVC light dosage probably isn’t able to disinfect anything:24

Can UVC damage my phone, my case or other protective equipment or materials?

Yes, UVC can damage materials, such as plastic, polymers and dyed textile. In general, it will degrade paint, turn plastics yellow and destroy air filters based on their composition2, 4, 10 . The problem is these are the materials used frequently in cases for phones, smartwatches and tablets and it’s what many devices are primarily made of.

With enough exposure, UV light can cause photodegradation, a chemical reaction that affects organic compounds causing the material to breakdown leading to changes in material and chemical properties. The degree of photodegration depends on the environment, including if there are any other chemicals or substances on the surface, the light intensity, and the degree of absorption, which depends upon the UV wavelength. For shorter UV wavelengths (with a lower UV wavelength number) they have a higher energy potential than longer wavelength UV. This has an accelerated aging effect on materials and paints.

In most plastics, it’s common to add UV stabilizers. This helps avoid aging from UV light which turns plastic yellow, and may cause it to become brittle, develop stress cracking, and make it more prone to breaking.  Most phone and device manufacturers do not factor this into the natural aging of the device, so this may impact the lifespan of the device and possibly invalidate or void the warranty of the device manufacturer. Use of these devices would also be outside the instructions of most manufacturers, and likely would invalidate any warranty.

Because it is also absorbed by these components, it can result in photo-degradation leading to the loss of material characteristics and properties.25

UVC may damage plants; therefore, hanging plants should not be placed in the disinfection zone in upper-room applications or in whole-room UVC applications19.

Given these safety issues, how are these devices regulated?

The FDA is responsible for regulating firms who manufacture, repackage, relabel, and/or import medical devices sold in the United States.

If the device is a medical device with claims for medical use, the device requires FDA clearance, approval, or authorization prior to marketing. A device is considered to be a medical device if it makes claims for medical use, e.g. stating it's for medical purposes; reduction or prevention of infection; prevention of any adverse health effect such as alleviation of allergies, asthma, et cetera; or if it claims to provide any specific

health benefits; or if it is for use on another medical device.

The FDA regulates electronic products that emit radiation (both non-medical and medical products), such as UVC lamps, through the Electronic Product Radiation Control Provisions, originally enacted as the Radiation Control for Health and Safety Act.

UVC lamp manufacturers are responsible for compliance with all applicable regulatory requirements, including Title 21 Code of Federal Regulations (CFR) Parts 1000 through 1004, and section 1005.25 and, as applicable, 21 CFR Chapter I, Subchapter H. The radiological health regulations include reporting of Accidental Radiation Occurrences, notification to the FDA and customers of radiation safety defects, and designation of a U.S. agent for imported lamps.

When a UVC lamp is regulated only as an electronic product, there are currently no specific FDA performance standards that apply. However if the device claims any function of a medical nature, it would then be subject to compliance with FDA regulations. Consumers can report a problem with a UVC lamp to the manufacturer and the FDA.

If the UVC lamp is not considered to be a medical device, it would be regulated under the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) as a pesticide device. If it is sold or distributed with claims to kill or be otherwise effective against viruses and/or bacteria, and unless an exception applies, the UVC manufacturer must comply with certain statutory and regulatory requirements.26

UV lights that are sold or distributed with claims that the product can be used for preventing, destroying, repelling or mitigating any pest (plant, animal, virus, bacteria or other microorganism) are federally regulated by EPA under FIFRA as a device, in particular FIFRA Sections 2(q) and Section 7.26

While not all UVC devices need to be EPA-registered, some states do require registration of devices that EPA does not regulate, or they may have other regulations that apply to devices. Devices need to be produced in an EPA-registered pesticide producing establishment, follow production reporting requirements under 40 C.F.R Part 167, and must be labelled per federal regulations at 40 C.F.R Part 156 to include warning and caution statements, directions for use and the EPA establishment number.24

More importantly, all marketing of any UVC device should be true including about the UVC effectiveness, safety, how it works and should be used and how it shouldn’t be used, and this should be supported by testing and documentation.

According to the EPA, there has been an increase in the production of unregistered, misbranded, and unproven pesticides and pesticide devices claiming to reduce or eliminate SARS-CoV-2 being offered for sale online27.

Any false marketing materials or false information on websites violate FIFRA Section 12(a)(1)(F), including if a manufacturer makes false or misleading statements about the UVC lamp’s effectiveness (known as efficacy), claims about the product’s safety that are untrue, false or misleading comparisons with other pesticides or devices, or any statement directly or indirectly implying that the device is recommended or endorsed by any Federal Government agency.

According to the EPA, consumers should beware of imposter disinfectant products that are being marketed online with potentially dangerous claims of protection against the novel coronavirus. EPA is working with the Department of Justice and other federal agencies to bring the full force of the law against those selling fraudulent or unregistered products.

In a press release from the EPA on Oct 15, 2020, they EPA said that “Unregistered disinfectants put consumers at risk. Whether these products are being sold to make a quick buck or are being sold out of ignorance, EPA will not allow the public to be endangered by companies taking advantage of the COVID-19 situation and selling ineffective products,” said EPA Regional Administrator Pete Lopez. “Disinfectants and other pesticide products that are not properly tested and registered can pose a serious risk to public health. EPA is working with public and private partners to ensure that pesticide products imported into, and sold in, the U.S. are safe and effective.” The EPA Administrator also has reached out to major retailers and third-party marketplaces to ensure that only approved disinfectant products are available for sale.27

If a UVC device claims to “Kill SARS-CoV-2”, it may be misleading if that device hasn’t been tested against the coronavirus SARS-CoV-2. “SARS-CoV-2” refers to a virus. “COVID-19” refers to a disease and diseases cannot be “killed.” Therefore, the claim “Kills COVID-19” is always considered false and misleading.

EPA advises consumers to use all pesticidal devices ONLY in accordance with the Directions for Use, which are required to appear on the product label. EPA recommends that consumers contact the manufacturer or seller of the pesticidal device directly if they have any questions about how to use the product, the product’s safety, or the product’s efficacy. All of these things should be documented since the EPA advises companies to maintain records with information and data to substantiate claims made in regard to devices.

If the UVC device is imported, then the manufacturer also needs to comply with the U.S. Customs and Border Protection (CBP) regulations set forth at 19 C.F.R. §§ 12.110 -12.117. The device must be in compliance with FIFRA prior to entry into the United States. The EPA has stopped imports of illegal pesticide products from entering the country working with the CBP.

To report a violation to the EPA, visit: https://www.epa.gov/enforcement/forms/enforcement-contact-us

For more on how what is the best procedure to keep surfaces and devices clean check out our recommended protocol here.

References:

 1. WHO, UV Lights and Lamps: Ultraviolet-C Radiation, Disinfection, and Coronavirus. https://www.who.int/health-topics/ultraviolet-radiation#tab=tab_1, World Health Organisation, (2020).

2. FDA. https://www.fda.gov/medical-devices/coronavirus-covid-19-and-medical-devices/uv-lights-and-lamps-ultraviolet-c-radiation-disinfection-and-coronavirus Medical Devices (2020).

3.  CDC. Miscellaneous Inactivating Agents: Guideline for Disinfection and Sterilization in Healthcare Facilities (2008). Infection Control https://www.cdc.gov/infectioncontrol/guidelines/disinfection/disinfection-methods/miscellaneous.html#anchor_1554329810 (2008).

4.  Irving, D. et al. A comparison study of the degradative effects and safety implications of UVC and 405 nm germicidal light sources for endoscope storage. Polymer Degradation and Stability 133, 249-254, doi:https://doi.org/10.1016/j.polymdegradstab.2016.09.006 (2016).

5  Gurzadyan, G. G., Görner, H. & Schulte-Frohlinde, D. Ultraviolet (193, 216 and 254 nm) photoinactivation of Escherichia coli strains with different repair deficiencies. Radiat Res 141, 244-251 (1995).

6 Chang, J. C. et al. UV inactivation of pathogenic and indicator microorganisms. Appl Environ Microbiol 49, 1361-1365, doi:10.1128/aem.49.6.1361-1365.1985 (1985).

7. Dai, T., Vrahas, M. S., Murray, C. K. & Hamblin, M. R. Ultraviolet C irradiation: an alternative antimicrobial approach to localized infections? Expert Rev Anti Infect Ther 10, 185-195, doi:10.1586/eri.11.166 (2012).

8.Scientific Reports, Nature Research, Far-UVC light (222nm) efficiently and safely inactivates airborne human coronaviruses, https://www.nature.com/articles/s41598-020-67211-2.pdf (2020)

9. Sliney, D. Balancing the risk of eye irritation from UV-C with infection from bioaerosols. Photochem Photobiol 89, 770-776, doi:10.1111/php.12093 (2013).

10. GLA. Position Statement on Germicidal UV-C Irradiation UV-C SAFETY GUIDELINES. https://www.globallightingassociation.org/images/files/publications/GLA_UV-C_Safety_Position_Statement.pdf Global Lighting Association (2020)

11. ACS. Ultraviolet (UV) Radiation. https://www.cancer.org/cancer/cancer-causes/radiation-exposure/uv-radiation.html American Cancer Society (2019).

12 . Szeto, W., Yam, W. C., Huang, H. & Leung, D. Y. C. The efficacy of vacuum-ultraviolet light disinfection of some common environmental pathogens. BMC Infect Dis 20, 127-127, doi:10.1186/s12879-020-4847-9 (2020).

13 . EPA. Ozone Generators that are Sold as Air Cleaners. https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-are-sold-air-cleaners USA Environmental Protection Agency (2020).

13 Kitagawa, H. et al. Effectiveness of 222-nm ultraviolet light on disinfecting SARS-CoV-2 surface contamination. American Journal of Infection Control, doi:10.1016/j.ajic.2020.08.022.

14. FDA. CFR – Code of Federal Regulations Title 21. https://www.accessdata.fda.gov/scripts/cdrh/cfdocs/cfcfr/cfrsearch.cfm?fr=801.415 U.S. Food & Drug Administration (2020)

15. Occupational Safety and Health Administration, Standard Interpretations / 8-hour total weight average (TWA) permissiable exposure limit (PEL) https://www.osha.gov/laws-regs/standardinterpretations/1995-10-06-3 United States Department of Labor (1995)

16. EPA. Cleaning up a Broken CFL https://www.epa.gov/cfl/cleaning-broken-cfl USA Environmental Protection Agency (2020).

17. National Library of Medicine. Germicidal Efficacy and Mammalian Skin Safety of 222-nm UV Light. https://pubmed.ncbi.nlm.nih.gov/28225654/ , (2017),

18. Nature, FDA. Depending on the glass envelope, small but significant levels of longer wavelengths may be of concern.23 Woods JA, Evans A, Forbes PD, Coates PJ, Gardner J, Valentine RM, Ibbotson SH, Ferguson J, Fricker C, Moseley H. The effect of 222-nm phototesting on healthy volunteer skin: A pilot study. Photodermatol Photoimmunol Photomed. 2015;31:159-66.(2020)

19. Illuminating Engineering Society, IES Committee Report CR-2-20 FAQs, https://www.ies.org/standards/committee-reports/ies-committee-report-cr-2-20-faqs/, (2020)

20. American Air & Water, Germicidal UV Dose, UV Irradiation Dosage Table https://www.americanairandwater.com/uv-facts/uv-dosage.htm, (2020).

21. Power Electronic Tips, Shedding light on how much UV-C you need for disinfection, https://www.powerelectronictips.com/shedding-light-on-how-much-uv-c-you-need-for-disinfection-faq , (2020)

22. N95Decon Research Document, Technical Report for UV-C Based N95 Reuse Risk Management, https://static1.squarespace.com/static/5e8126f89327941b9453eeef/t/5f39ec50d689050994c07338/1597631576383/20200826_N95DECON_UVC_technical_report_v2_1.pdf (2020).

23. Wiley Online Library, UVC Germidical Units: Determination of Dose Received and Parameters to be Considered for N95 Respirator Decontamination and Reuse, https://onlinelibrary.wiley.com/doi/full/10.1111/php.13322, (2020)

24. Power Electronic Tips, When it comes to UV-C LED lights, buyer beware, https://www.powerelectronictips.com/when-it-comes-to-uv-c-led-lights-buyer-beware (2020)

25. Singh, B. & Sharma, N. Mechanistic implications of plastic degradation. Polymer Degradation and Stability 93, 561-584, doi:https://doi.org/10.1016/j.polymdegradstab.2007.11.008 (2008).

26. EPA, Compliance Advisory: EPA Regulations about UV lights that Claim to Kill or Be Effective Against Viruses and Bacteria, https://www.epa.gov/sites/production/files/2020-10/documents/uvlight-complianceadvisory.pdf Environmental Protection Agency United States, (2020)

27. EPA, EPA Takes Action to Protect Public from Coronavirus Protection Scams, https://www.epa.gov/newsreleases/epa-takes-action-protect-public-coronavirus-protection-scams, (2020)

 

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