What is the UVC dose for killing or disabling the COVID-19 virus?

Because the COVID-19 virus (SARS-CoV-2) is so new, the scientific community doesn’t yet have a specific deactivation dosage. However, we know the dosage values for comparable viruses in the same SARS virus family are 10-20 mJ/cm² using direct UVC light at a wavelength of 254nm; this dosage will achieve 99.9% disinfection (i.e., inactivation) under controlled lab conditions. In real-life, the virus is often hidden or shaded from direct UVC light, reducing UVC’s effectiveness. To compensate, researchers are applying dosages of 1,000 - 3,000 mJ/cm² to ensure 99.9% deactivation, the current CDC disinfection goal (see CDC’s recently published guidelines, online).

CDC’s recently published guidelines

Can we use tanning beds to decontaminate PPE?

No. Tanning beds are not considered useful to decontaminate PPE. The lamps in tanning beds are emitting a spectrum of UVA and UVB, wavelengths between 300-400 nm. While there is some antimicrobial efficacy in the UVB spectrum, it is generally pretty low. The UVC portion of the spectrum, 220-280 nm, is much more effective for disinfection. Therefore, I’m afraid that tanning beds cannot be relied upon for this purpose. Theoretically, you could replace the lamps in a tanning bed with those that emit UVC, but you’d also have to remove the acrylic bed surface because UVC does not transmit through that material. By the time you do that much modification to the bed, you may as well build a simple disinfection device using UVC lamps from scratch.

Can we use UVC disinfection to reuse our N-95 masks as our supplies are limited?

There are several manufacturers now offering equipment dedicated to disinfecting N95 masks. Please visit the IUVA supplier listings. Note that the IUVA does not endorse any product. This list is intended to highlight vendors who are self-identifying as having devices that may be helpful during the covid-19 pandemic.

That being said, the research community is scrambling right now to try to answer some of these questions as quickly as possible. See the following for some preliminary “educated guesses” about how to do it, in the context of disinfecting hospital masks. https://www.nebraskamed.com/sites/default/files/documents/covid-19/n-95-decon-process.pdf

There is some thought in the UV community that UVC together with some other process, notably heating to 65C in a humid environment, or hydrogen peroxide vapor, might be a good multi-barrier process. The heating or hydrogen peroxide vapor can penetrate into material better than UV and is believed to be able to kill the SARS-CoV-2 virus, but it may be less effective against many of the other pathogens that still exist in hospital settings. The UVC can supplement the virus kill, while also killing many of these other pathogens.

IUVA supplier listings

Can the products I find on websites such as Amazon be safely used for medical disinfection?

Devices sold on general marketplaces such as Amazon and Alibaba are not regulated for their UV output, and devices sold as UV-C emitters cannot be guaranteed to perform as described. UV-C sources and devices should be purchased from trusted, reputable suppliers. Please consult with the supplier and see the IUVA Advice for further guidance.

IUVA Advice

Can You Use UVC for direct human disinfection?

UVC is damaging to the skin and to the eyes. DO NOT look at the UV light or expose any part of your body. UVC should not be, and is not intended for, use for direct human disinfection.

A possible exception is far UV light (see the FAQ that is specific to far UV light).

How do operators remain safe when using UVC lights to clean surfaces?

• Like any disinfection system, UVC devices must be used properly to be safe.
• They all produce varying amounts of UVC light in wavelengths of 200 – 280nm. UVC light is much more energetic than normal sunlight, and can cause a severe sunburn-like reaction to your skin, and similarly, could damage the retina of your eye, if exposed.
• 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, in general, machine-human safety needs to be considered with all disinfection devices.
• Suitable PPE should be worn at all times when there is a risk of UV exposure to the skin or eyes. Be aware of stray light from the UV source and avoid irradiation of reflective surfaces.
• These considerations should be addressed in the operations manual, in the user training, and appropriate safety compliance.

Would the use of UVC at 185nm wavelength, which generates ozone, be as effective as germicidal UVC or only 254nm?

Studies have shown that UVC light at wavelengths of 254nm-265nm disrupts the DNA/RNA replication process in the cells. Ozone is a toxic chemical produced by 185nm UVC light interacting with oxygen in the air, that disinfects much like any chemical disinfectant. While ozone does dissipate in time, it can be corrosive and its effects on the item being treated needs to be understood before being used. Also, it is a lung irritant, and is regulated by NIOSH as a known safety hazard.

Where can I find third-party testing of the efficacy of UVC lights?

Some suppliers of third party testing are listed in our IUVA supplier listings.

IUVA supplier listings

We are looking into the use UVC light to disinfect certain areas of the electric power plants. Have you done any research on the noise that these devices can induce into electronics (EMI/RFI effect)?

Most UVC disinfection devices make UVC light using a fluorescent-light bulb; the bulb is unique, but otherwise the device uses ballasts, wiring and controls similar to any other fluorescent light fixtures. Other sources include LEDs (typically low voltage/low current) or xenon flash bulbs (using high voltage capacitor discharge circuits). The potential for EMI/RFI effects will vary accordingly.

Can you tell us more about the penetration of UVC through "normal household" items?

There is essentially zero penetration of UVC into any solid material that doesn’t otherwise transmit it – it would all be absorbed within a few microns. There are only a scant few materials that do transmit UVC: high-purity silicate glasses, very thin sections of certain fluoropolymers, sapphire, and some other crystals. Most other polymers, even if visibly transparent, are not at all transmissive UVC. I think thin sections of pure polyethylene can transmit some UVC, depending on its microstructure and how it was processed. It is probably safe to say that a thin enough film of any polymer could transmit UVC to some degree.

Depending on how thick a cotton T-shirt is, it may allow some UVC to get through because of porosity (gaps between fibers/yarns) and some tiny amount of internal reflection, but otherwise cotton fibers do not transmit UVC, per se.

Cardboard is as good as a brick wall. White paper or cardstock might transmit a bit of UVC based on the same principle like the cotton textile, but likely not much.

Two generic tips:

• For a disinfection application in which you WANT something exposed to UVC, assume it has no penetration into the material at all. It is only a surface phenomenon.
• For a shielding application in which you DON’T want exposure to UVC, if you cannot see blue light from the lamp getting through the material, it is safe to assume that you have also blocked all the UVC.

How can you tell if "UV protective" glass and glass films are actually treated to block UVA rays. Is there an easy way to tell?

If you can get access to a UV spectrophotometer. which can record the transmittance of the glass or film as a function of wavelength, you can easily see if the UV rays (less than 400 nm) are blocked.

One other way would be to get access to a UV lamp that is used in sun tanning parlors. If you expose this UV light to a white shirt, the shirt will glow blue due to fluorescence from the pigments in the shirt (this is the common “disco” effect). If you place the glass or film between the UV lamp and the shirt, the blue glow will disappear if the material blocks UV.

We keep seeing the terms ‘watts’ and ‘joules’ in descriptions of how much UV is required to disinfect something. What do these terms mean? Are they the same? Why are they important?

Most people seem to be familiar with the term ‘watts' (from light bulbs and electric bills); but probably not the term ‘joules' (a metric measurement term). In short, both are used in measuring energy in any form (e.g., electricity as well as light):

• A Watt is a measure of the rate of energy delivery (analogous to gallons-per-minute flow rate for water delivery).
• A Joule is a cumulative measure of the total amount of energy delivered (analogous to total gallons of water delivered).

It usually is associated with how much time was needed to deliver the energy.

The way the units work is 1 Joule (J) of energy delivered = delivering 1 Watt (W) of energy for 1 second. In the UV world, we usually measure things in small increments, i.e., thousandths of a Joule or Watt. These are shown as ‘milli-Joules' (i.e., ‘mJ’ or 1/1,000 of a Joule), and milli-Watts (i.e., ‘mW’ or 1/1,000 of a Watt).

Example: 40mJ (cumulative energy) = 10mW delivered for 4 seconds

Is far UV (200 – 225 nm) a promising disinfection technique to address COVID-19 and other pathogen disinfection?

Yes, in 2021 IUVA created an Task Force to review the current knowledge of Far UV-C. A “white paper” developed by the Task Force can be found here: https://iuva.org/resources/covid-19/Far%20UV-C%20Radiation-%20Current%20State-of%20Knowledge.pdf. As with all UV-C solutions we need accurate inactivation (dose) response curves to determine the UV exposure (UV dose) required for the desired level of disinfection. Existing literature indicates that Far UV-C can be effective in inactivating SARS-CoV-2 and other airborne pathogens (e.g., those that cause influenza and the common cold), given sufficient UV exposure.

Is far UV (200 – 225 nm) 'skin safe'

Far UV-C is high-energy radiation which can directly damage DNA and key organic molecules such as proteins. The biophysical basis for the claims that Far UV-C is ‘skin and eye safe’ is that the damaging radiation is entirely absorbed within the outer, dead, layers of skin and eye and does not reach the inner, live cells; if the radiation were to hit these cells (which happens at longer wavelengths like 254 nm or longer), they would be damaged as a result. An increasing number of studies have been published discussing acute and chronic exposure to Far UV-C, most commonly using optically-filtered Kr-Cl excimer lamps. These studies have investigated the effects of Far UV-C radiation on mice and human tissues by measuring key chemical and physical changes known to indicate damage from UV-C exposure. It was found that these same damage indicators were not observed under Far UV-C irradiation. (Yamano et al., 2022, Yamano et al. , 2022; Buonanno et al., 2017; Narita et al., 2018)

Additionally, the exposure of humans to ultraviolet radiation is the subject of numerous regulations and standards worldwide: 2006/25/EC (Europe), ACGIH 2022 TLVs (USA), and IEC 64271 (CB Scheme, global) all employ an actinic UV hazard curve which lists all UV-C, including Far UV-C, as potentially harmful, though the Far UV-C range being the least (and significantly less than 254nm or longer wavelengths). These standards therefore define an upper limit to how much Far UV-C radiation the human body can be exposed to. This would then need to be compared to the dose that humans are being exposed to over typically 8 hours.

Does far UV (200 – 225 nm) generate ozone?

From a photochemical perspective, yes.

The Chapman cycle (Chapman, 1930) describes the counteractive processes of ozone formation and degradation from the interaction of electromagnetic radiation with molecular oxygen (O2) and ozone (O3). The rate of generation of ozone by Far UV-C (known as the Herzberg continuum in atmospheric science) outweighs the rate of its degradationFar UV-C (200-230 nm) only generates ozone in the upper atmosphere, where path lengths are very long. In a normal laboratory setting, ozone would not be generated because oxygen (O2) is a very weak absorber in the Far UV-C region.

As with any process, the risk of such hazards should be assessed on an application-by-application basis. A low power lamp operated in a ventilated area will likely not generate a measurable ozone concentration; a high-power system in an enclosed space may constitute a substantial risk.

For more information, or if you are at all uncertain, please contact your vendor for guidance and apply suitable risk management procedures.