Using Far-UVC Light To Kill Airborne Human Coronaviruses

[ZapperZ]

TL;DR Summary

Using Far-UVC to kill airborne cononavirus - but is it as safe to human as we already know?

I know that there are at least a couple of threads related to COVID-19 scattered over PF, but I want to get a specific feedback on this latest research in terms of human health and safety.

This paper was published in Nature, and it presented a rather fascinating result if it is true. The researcher used far-UVC light (222 nm wavelength) to kill the viruses in airborne aerosol with a claim based on the current guidelines that far-UVC is not as harmful as UVA and UVB.

We know that UVC is used to sterilized stuff and can kill viruses, but it is also harmful to human. But far-UVC, with a shorter wavelength, appears to have very short penetration depth, making it less prone to affect human cells:

... far-UVC light has a range in biological materials of less than a few micrometers, and thus it cannot reach living human cells in the skin or eyes, being absorbed in the skin stratum corneum or the ocular tear layer.

In the end of their reports, this is their conclusion:

In conclusion, we have shown that very low doses of far-UVC light efficiently kill airborne human corona-viruses carried by aerosols. A dose as low as 1.2 to 1.7 mJ/cm2 of 222-nm light inactivates 99.9% of the airborne human Coronavirus tested from both genera beta and alpha, respectively. As all human coronaviruses have similar genomic size, a key determinant of radiation sensitivity27, it is likely that far-UVC light will show comparable inactivation efficiency against other human coronaviruses, including SARS-CoV-2.

According to the article, the safety limit for human exposure to far-UVC is

... a regulatory limit as to the amount of 222 nm light to which the public can be exposed, which is 23 mJ/cm2 per 8-hour exposure ..

They showed that they can "inactivate" 99.9% of the airborne viruses in just 25 minutes at that exposure rate, well below the regulatory limit. This means that, human and far-UVC may live together, with the ability to greatly reduce the amount of airborne viruses in aerosols.

My question is, how strong is the evidence that far-UVC is that safe for human, especially for our eyes. The authors gave ref. 12-15 as sources that claim that this type of EM radiation is relatively safe to human. Anyone here knows a bit more about this biological effects? If this is true, then it can definitely reduce one of the possible source of transmission of the flu and other illness due to airborne transmission.

Zz.

 

[jim mcnamara]

Here is a yes answer:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5552051/
UVC used during surgery to prevent mammalian wound infection by bacteria. For example, human skin samples exposed to this light regime show no DNA damage

Conclusion:

far-UVC light in the range of 200–222 nm kills bacteria efficiently regardless of their drug-resistant proficiency, but without the skin damaging effects associated with conventional germicidal UV exposure. [252nm]

There are a lot of papers on this subject.

 

[ZapperZ]

Here is a yes answer:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5552051/
UVC used during surgery to prevent mammalian wound infection by bacteria. For example, human skin samples exposed to this light regime show no DNA damage

Conclusion:

There are a lot of papers on this subject.

Is there a paper on long-term effect on the cornea or human eye?

Zz.

 

[Ygggdrasil]

This paper was published in Nature,

Just a quick note: the paper was not published in the journal Nature, but published in the journal Scientific Reports, an open access journal owned by the company that owns Nature. However, Scientific Reports (impact factor 4.011) is a much less prestigious journal than Nature (impact factor 43.070).

(Impact factors are imperfect measures of journal quality, but I'm just using them here to illustrate in a more objective way how the scientific community views the quality of the two journals).

 

[jim mcnamara]

Older paper on the subject shows considerable rabbit corneal damage on exposure to far UVC.
https://pubmed.ncbi.nlm.nih.gov/464507/
As a guess only and without evidence, a safe bet: it would not be wise to be exposed to far UVC without eye protection.

 

[ZapperZ]

Older paper on the subject shows considerable rabbit corneal damage on exposure to far UVC.
https://pubmed.ncbi.nlm.nih.gov/464507/
As a guess only and without evidence, a safe bet: it would not be wise to be exposed to far UVC without eye protection.

Thanks. Unfortunately, I don't have access to such a journal. The abstract doesn't say much in terms of exposure time. I also don't know what ".. 105 - 8 x 105 erg/cm2 ..." means. I can guess it is a 10⁵ magnitude, but "105 - 8" I can't quite decipher.

It appears that the intensities that were used were considerably higher than in the study that I cited (order of mJ/cm²). Still, maybe when the far-UVC light is on, everyone should be wearing some form of eye-protection.

Zz.

 

[Tom.G]

105 - 8 x 105 erg/cm2 ..." means. I can guess it is a 105 magnitude, but "105 - 8" I can't quite decipher.

From context, I get "105 - 8 x 105 erg/cm2" to mean "10⁵ to 8 x 10⁵ erg/cm²".

I'll let others here convert 'erg/cm2' (erg/cm²) to mJ.

Cheers,
Tom

 

[Eric Bretschneider]

Older paper on the subject shows considerable rabbit corneal damage on exposure to far UVC.
https://pubmed.ncbi.nlm.nih.gov/464507/
As a guess only and without evidence, a safe bet: it would not be wise to be exposed to far UVC without eye protection.

Generic UV-C encompasses a rather large swath of the spectrum. The range of 200 nm - 320 nm represents photon energies of 5.58 eV - 3.87 eV. For the chemically inclined that equates to 374 kJ/mol to 539 kJ/mol.

Absent references to specific ranges of wavelengths you shouldn't compare reports of cell damage.

 

[jim mcnamara]

@Eric Bretschneider
Good point. However if you read the abstract, they cite energies. Or some confusing numbers, anyway.
I am not defending the quality, just presenting the extent (or lack ) of knowledge.

The important part is the fact that there is a full page of PubMed citations on tissue damage from UVC.

Your assessment of the energies is correct. Just change the upper bound down somewhat to ~252nm

Yes, this is hand-wavy. But older medical literature is like that. So consider them as case reports. They certainly have confounding factors.

 

[ZapperZ]

I think that's why I'm asking about this to people who are more familiar with publications in this field. Coming purely from physics background, I find many of these papers a bit more challenging to decipher accurately, and certainly hunting for relevant references via Google Scholar doesn't tell me the whole picture.

Zz.

 

[Eric Bretschneider]

@Eric Bretschneider
Good point. However if you read the abstract, they cite energies. Or some confusing numbers, anyway.
I am not defending the quality, just presenting the extent (or lack ) of knowledge.

The important part is the fact that there is a full page of PubMed citations on tissue damage from UVC.

Your assessment of the energies is correct. Just change the upper bound down somewhat to ~252nm

Yes, this is hand-wavy. But older medical literature is like that. So consider them as case reports. They certainly have confounding factors.

The problem is the dosage is energy only. It ignores wavelength. You can deliver the same energy at 690 nm and you will get a far different result. Transmission through tissue is highly wavelength dependent in the short wavelength range for UV-C.

 

[Laroxe]

Of the systems in use there are the large units that can be left in areas for prolonged periods of time and smaller units used to reduce air born pathogens. Their effectiveness is highly dependent on the intensity and the distance from the source has a significant effect. One potential problem with using far-UVC is that at this wavelength there is an increased potential for the generation of Ozone, so its safety remains debatable when used in occupied environments..

 

[ZapperZ]

Of the systems in use there are the large units that can be left in areas for prolonged periods of time and smaller units used to reduce air born pathogens. Their effectiveness is highly dependent on the intensity and the distance from the source has a significant effect. One potential problem with using far-UVC is that at this wavelength there is an increased potential for the generation of Ozone, so its safety remains debatable when used in occupied environments..

I've been trying to look more into this, and decided to go to the "authority" and see what their official opinion is on this matter. The International Ultraviolet Association (I didn't know such an organization existed till recently) has a FAQ, and a few of them are on far-UVC. The issue of ozone generation is one of the FAQ, and this is what they wrote:

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 light 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 degradation; the tipping point at which this generation/degradation balance flips is ~242 – 243 nm. (Andrew et al., 2003; Santos, Burini, and Wang, 2012), Far UVC (200-225 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 UVC 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 well-ventilated area may not generate a measurable ozone concentration; a high-power system in an enclosed space may constitute a substantial risk.

Now, I'm not sure how path lengths have anything to do with ozone production in this case, but I can understand how the far-UVC range may be a "... very weak absorber..." may reduce ozone production. Unfortunately, being at home, I do not have access to the two references they cited.

So if anyone has anymore info on this...

Zz.

 

[Pratyeka]

Sterilray and Ushio are about to sell far UV-C lamps to the public and institutions. You can check their research
https://sterilray.com/
https://www.ushio.com/product/care222-mercury-free-far-uv-c-excimer/

 

[Tom.G]

Sterilray and Ushio are about to sell far UV-C lamps to the public and institutions. You can check their research
https://sterilray.com/
https://www.ushio.com/product/care222-mercury-free-far-uv-c-excimer/

Interesting.
I read the White Paper report on the USHIO site about disinfecting a conference room. Unfortunately it is only a sales pitch. The results look good but neither the lamp power nor the room size are given. There are irradiated power contours given but the location of the microbial tests are not shown.
These omissions make the report rather useless. Oh well.

 

[TeethWhitener]

Just a quick note: the paper was not published in the journal Nature, but published in the journal Scientific Reports, an open access journal owned by the company that owns Nature. However, Scientific Reports (impact factor 4.011) is a much less prestigious journal than Nature (impact factor 43.070).

(Impact factors are imperfect measures of journal quality, but I'm just using them here to illustrate in a more objective way how the scientific community views the quality of the two journals).

It’s probably important to point out that Scientific Reports has an interesting publishing philosophy that I think most people don’t know about: the reviewers are not allowed to judge the paper based on its perceived importance or potential impact on the field. They can only judge on the soundness of the data collection and analysis. The idea is to let the broader scientific community decide for itself whether the findings are noteworthy, rather than leaving that judgment in the hands of a few editors and reviewers.

 

[shjacks45]

Bad idea. Air becomes opaque at low wavelength, energy absorbed by Oxygen turning to Ozone and creating singlet Oxygen (Oxygen is usually inert). Although the skin stops most of this radiation, q.v. skin cancer. Mercury germicidal (Ozone) lamps emit at 184nm and 254 nm, both of which cause extensive DNA damage which is what kills bacteria and makes cancer in people. Coronavirus takes cells' membrane when created, so as vulnerable as human cells to soap, and other toxics. Human cell membranes have markers that tell the immune system its friendly. UVA is too low energy light to damage human DNA and also activates DNA repair. Titanium Dioxide (paint) activates Oxygen (air) with blue light to oxidize surface contamination. Stores like Office Depot and Costco used to use high pressure mercury vapor lights (cheapest cost per lumen then) that caused the beige plastic on computers to yellow (UV exposure) and (yes, I tested for Ozone) employees had respiratory problems.

 

[ZapperZ]

Bad idea. Air becomes opaque at low wavelength, energy absorbed by Oxygen turning to Ozone and creating singlet Oxygen (Oxygen is usually inert). Although the skin stops most of this radiation, q.v. skin cancer. Mercury germicidal (Ozone) lamps emit at 184nm and 254 nm, both of which cause extensive DNA damage which is what kills bacteria and makes cancer in people. Coronavirus takes cells' membrane when created, so as vulnerable as human cells to soap, and other toxics. Human cell membranes have markers that tell the immune system its friendly. UVA is too low energy light to damage human DNA and also activates DNA repair. Titanium Dioxide (paint) activates Oxygen (air) with blue light to oxidize surface contamination. Stores like Office Depot and Costco used to use high pressure mercury vapor lights (cheapest cost per lumen then) that caused the beige plastic on computers to yellow (UV exposure) and (yes, I tested for Ozone) employees had respiratory problems.

i don't think you've read the topic of this thread carefully enough.

it is NOT a means to treat sick people. It is also looking specifically in the far-UVC range.

You may want to read the article and links given.

Zz.

 

[chemisttree]

I wonder if the effects are due to the ozone produced? Has anybody measured ozone in these tests?

 

[Secan]

I don't want to create a new thread just for this question, which is related to this thread.

Can common uv sterilizer box (enclosed) kill the Coronavirus in the faceshield (with all surfaces exposed, i know it can't kill the viruses hidden in the n95 or surgical masks).

What follows is the uv sterilizer powered with double philips uv lamps (specs below) sterilizing the faceshield. Would it theoretically work? I'm asking "theoretically" and not definitely so do not worry about taking responsibility.

We are in a global emergency so sharing the specification may not a bad idea as I want to emphasize whether uvc lamp with a peak at 253.7nm can disinfect faceshield if all surfaces are exposed for say 15 minutes.

 

[ZapperZ]

But isn't that what is already being done with UV sterilization? This as long as a surface is exposed to such UV such as UVC, it'll zap such viruses. I don't believe that there is any doubt about that here.

Zz.

 

[Secan]

But isn't that what is already being done with UV sterilization? This as long as a surface is exposed to such UV such as UVC, it'll zap such viruses. I don't believe that there is any doubt about that here.

Zz.

Can it also zap the Covid virus? Its a special virus. I want to see data uvc can really kill the Covid virus. Is there any? Before considering airborne decontamination.

 

[ZapperZ]

Can it also zap the Covid virus? Its a special virus. I want to see data uvc can really kill the Covid virus. Is there any? Before considering airborne decontamination.

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).

It is all in the IUA FAQ that I had already linked to. So far, based on the biology of the COVID-19 virus, there's nothing to indicate that it will not follow the same SARS virus-type behavior.

Zz.

 

[shjacks45]

i don't think you've read the topic of this thread carefully enough.

it is NOT a means to treat sick people. It is also looking specifically in the far-UVC range.

You may want to read the article and links given.

Zz.

I think the topic is germicidal properties of UVC. It kills living things and popular in the dark old days of the 1900s, and there are alternatives in our current era. The exposure limit is archaic, and based on acceptable harm as are many federal industrial regulations. You see 'uvc stopped by skin' like scientists in the 1800s thought x-rays are safe because they go right through you. It is common in this day and age to read research papers where conclusions don't match experimental results, and most papers like the one listed here have not been replicated or peer reviewed. See Wikipedia "Ultraviolet" article, ultraviolet radiation (UVR), defined most broadly as 10–400 nanometers, can be subdivided into a number of ranges recommended by theultraviolet radiation is subdivided into a number of ranges recommended by the ISO standard ISO-21348, and you are disagreeing with the Standards body.

 

[ZapperZ]

I think the topic is germicidal properties of UVC. It kills living things and popular in the dark old days of the 1900s, and there are alternatives in our current era. The exposure limit is archaic, and based on acceptable harm as are many federal industrial regulations. You see 'uvc stopped by skin' like scientists in the 1800s thought x-rays are safe because they go right through you. It is common in this day and age to read research papers where conclusions don't match experimental results, and most papers like the one listed here have not been replicated or peer reviewed. See Wikipedia "Ultraviolet" article, ultraviolet radiation (UVR), defined most broadly as 10–400 nanometers, can be subdivided into a number of ranges recommended by theultraviolet radiation is subdivided into a number of ranges recommended by the ISO standard ISO-21348, and you are disagreeing with the Standards body.

First of all, the publication in the original post is rather new. So you are comparing what is already known with something that is still be researched on.

Secondly, this issue is not about all UV, or even all UVC. It is specific to far-UVC, and in particular, the 220 nm wavelength that was used in this study. There are already considerable amount of study in this particular range that seem to indicate that it is not as harmful to human as other forms of UVC:

https://physicsworld.com/a/the-potential-of-far-ultraviolet-light-for-the-next-pandemic/

But not all wavelengths of UVC are as damaging as others, as a group of researchers led by physicist David Brenner at Columbia University in New York, US, showed in 2017. Their research relied on an excimer lamp – a type of light tube containing molecules, or excimers, that can briefly exist in an excited electronic state before returning to their ground state, and in doing so emit UV radiation at various wavelengths in the UVC band depending on the molecules used. On exposing mice to 222 nm, far-UVC light from a krypton-chlorine excimer lamp, Brenner and colleagues found no evidence of skin damage, even though they found that the same light was effective at killing the superbug MRSA (Radiat. Res. 187 493).

The result was corroborated a year later by Kouji Narita at the Hirosaki University Graduate School of Medicine in Japan and colleagues. This team also confirmed that the 254 nm-wavelength emission of a conventional germicidal lamp did induce sunburn-like skin damage (PLOS One 13 e0201259). That same year, Brenner and colleagues found that 222 nm light is able to destroy airborne viruses as well. In their test, with an exposure of just 2 mJ/cm2, the far-UVC radiation safely inactivated more than 95% of airborne H1N1 influenza, the virus behind the 2009 swine flu pandemic (Sci. Rep. 8 2752). There is even evidence that far-UVC light is safe for the eyes: last year, Sachiko Kaidzu of Shimane University in Izumo, Japan, found no damage to the corneas of rats exposed to 222 nm electromagnetic radiation (Free Radic. Res. 53 611).

Many of these results are still new and I, for one, never advocated that we all go out and buy such UV sources and install them right now! Safety studies should never be a rushed job! But these results counter your argument there are no indication that there are any form of "safe" UV radiation. If you do not buy these results, I'd like to see your rebuttal sent to one or more of these published papers. And I do not know where you got the idea that the paper I cited "... have not been replicated or peer reviewed ... ". Read above!

Finally, I'm an experimental physicist. I've dealt with 252 nm Class 4 UV laser for a particle accelerator that is powerful enough to cause severe skin burn. And I've also had to deal with safety issues and documentations for the operations of our facility. So I am fully aware of the hazards surrounding this class of UV radiation. It was why I was surprised at the results surrounding far-UVC, and why I asked it in the Medical forum, because till recently, I considered almost all UV radiation as unsafe to human exposure at varying degrees.

Zz.

 

[.Scott]

For air cleaning, I'd put it in a box.

I purchased a regular 254 nm UVC lamp from Walmart - they're fairly inexpensive.
Should I need it for a COVID-19 household member, I will put it in a box with light-blocking baffles on each side and a fan that will slowly circulate air through it. This may not kill all of the COVID-19, but it should keep the concentration down.
Of course, if the weather is fair, I would just open a window.

Although UVC in the 200-225 nm range is more effective at killing Coronaviruses, I have a couple of questions about them:
1) I don't want 185nm (ozone) - and the 254nm lamp are made from a glass that blocks this. Can (and do) lamps in the 200-225 nm range also block 185?
2) 254 nm UVC lamps are easy to get - as I said I got mine at Walmart. Where would I purchase a lamp in the 200-225 nm range? Are these consumer goods or just for lab use?

 

[BillTre]

For air cleaning, I'd put it in a box.

I purchased a regular 254 nm UVC lamp from Walmart - they're fairly inexpensive.
Should I need it for a COVID-19 household member, I will put it in a box with light-blocking baffles on each side and a fan that will slowly circulate air through it. This may not kill all of the COVID-19, but it should keep the concentration down.

This would be a lot like a UV unit in an HVAC system. Not that unusual.
A similar thing is done in aquacultural water systems. The water is recirculated through pumps and filters. In the process the water can also be passed over submerged UV lamps.
This is one of two or three ways to control disease spread in high density water systems:

• Mechanically filter out infectious particles (not easy to get such small particles)
• UV illuminate to kill infectious particles (mostly single celled, clean water)
• Chemically treat the water separate from the animalls: usually ozone (O₃) is used to chemically oxidize water, in an area separate from the animals (which can be damaged). The ozone in the water is then either treated to remove the ozone (usually with UV illumination) or wait a period of time for the ozone to dissipate, before its eventual return to the animals' housings.

 

[Pratyeka]

Here is a paper on far UVC published in Nature open access on June 24 2020
https://www.nature.com/articles/s41598-020-67211-2

 

[ZapperZ]

Here is a paper on far UVC published in Nature open access on June 24 2020
https://www.nature.com/articles/s41598-020-67211-2

Er... isn't this the exact paper that I cited in the very first post of this thread?

{scratching head}

And you also neglected to address the issue in your earlier post in this therad:
https://www.physicsforums.com/threa...borne-human-coronaviruses.991363/post-6368103

Zz.

 

[Vanadium 50]

Why read when you can write!

 

[Pratyeka]

Er... isn't this the exact paper that I cited in the very first post of this thread?

Sorry, I picked the wrong thread, and I don't know how to delete my post.

 

[James Demers]

I'm not sure how path lengths have anything to do with ozone production

With a weak absorber like O2, a photon needs a lot of encounters with the molecule to have a fair probability of being absorbed. You get that passing through miles of atmosphere, but not in passing across a room.

Far-UV-C doesn't penetrate to skin cells' DNA, but that happens because it gets absorbed and deposits its considerable energy in the outermost layers of the skin. That will surely lead to photochemcal damage, but it's dead skin that's going to be shed anyhow, so overall, it's "safe". The cornea is another matter - it can repair itself, but there's no sacrificial layer, so at best we're talking about reversible damage, quite possibly with considerable discomfort. Eyeglasses or goggles would be highly advisable, but at least they don't have to be specialized UV filters.
Keep in mind that the proposed use, as a preventative measure, calls for constant, all-day exposure.
This raises the question of everything else in the room: Metals will be unaffected, but fabrics, paints, plastics, and surface finishes of all kinds will suffer from prolonged exposure. This, I think, is what makes far-UV-C illumination impractical in most environments. At best, you could circulate the room's air through an enclosed irradiator, reducing but not entirely eliminating airborne pathogens. Whether or not it affords effective protection from SARS-CoV-2, I bet you could get rich selling such units.

 

[DaveE]

This is a good interview with one researcher of Far UVC sterilization:
https://www.microbe.tv/twiv/twiv-666/

 

[Eric Bretschneider]

With a weak absorber like O2, a photon needs a lot of encounters with the molecule to have a fair probability of being absorbed. You get that passing through miles of atmosphere, but not in passing across a room.

Far-UV-C doesn't penetrate to skin cells' DNA, but that happens because it gets absorbed and deposits its considerable energy in the outermost layers of the skin. That will surely lead to photochemcal damage, but it's dead skin that's going to be shed anyhow, so overall, it's "safe". The cornea is another matter - it can repair itself, but there's no sacrificial layer, so at best we're talking about reversible damage, quite possibly with considerable discomfort. Eyeglasses or goggles would be highly advisable, but at least they don't have to be specialized UV filters.
Keep in mind that the proposed use, as a preventative measure, calls for constant, all-day exposure.
This raises the question of everything else in the room: Metals will be unaffected, but fabrics, paints, plastics, and surface finishes of all kinds will suffer from prolonged exposure. This, I think, is what makes far-UV-C illumination impractical in most environments. At best, you could circulate the room's air through an enclosed irradiator, reducing but not entirely eliminating airborne pathogens. Whether or not it affords effective protection from SARS-CoV-2, I bet you could get rich selling such units.

The layer of tears over the cornea is mostly water which is itself a strong absorber of far UV-C (i.e. 222 nm). Its not exactly a sacrificial layer, but it is readily replenished.

There also isn't a lot of information on the effect of far UV-C light on surfaces and materials. It isn't exactly a common wavelength. Those sources that do emit significant amounts (welding arc, deuterium lamps, etc.) are broad band emitters, so you have to sort out what wavelengths have an effect.