Intro to Far-UV 🧵
Far-UV is possibly the best tool we have against COVID and very few people actually know what it is. Here's an intro of what it is, effectiveness, safety and how it's created.
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Far-UV is possibly the best tool we have against COVID and very few people actually know what it is. Here's an intro of what it is, effectiveness, safety and how it's created.
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TLDR - Far UV is a range of UV light that you can expose people to in comparatively high doses to other UV light. You can safely shine it in an occupied room and it will be extremely effective at killing airborne microbes. This can't be done with other UV light.
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What is Far-UV?
UV is broken up into 3 ranges:
UVA: 315-400 nm
UVB: 280-315 nm
UVC: 100-280 nm
Far-UV is a range of UVC light between 200-230 nm. It's "far away" from visible light. Near UV is 300-400 nm.
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UV is broken up into 3 ranges:
UVA: 315-400 nm
UVB: 280-315 nm
UVC: 100-280 nm
Far-UV is a range of UVC light between 200-230 nm. It's "far away" from visible light. Near UV is 300-400 nm.
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UVC wavelengths are good at killing microbes. When it's used for that purpose, it's called ultraviolet germicidal irradiation (UVGI) or germicidal ultraviolet (GUV). It can disinfect air, water and surfaces.
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Effectiveness
The best data we have so far is this experiment. A 15 W far UV lamp in a 32 m³ room gives 33-66 equivalent air changes per hour. A CR box would give you 15 eACH. So 1 far-uv lamp = 2-4 CR boxes in a typical room in your home.
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nature.com/articles/s4159…
The best data we have so far is this experiment. A 15 W far UV lamp in a 32 m³ room gives 33-66 equivalent air changes per hour. A CR box would give you 15 eACH. So 1 far-uv lamp = 2-4 CR boxes in a typical room in your home.
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nature.com/articles/s4159…
You can easily scale this up. Using 5 lamps, it provided 128-322 eACH (like 9-14 CR boxes in your dining room. Can you imagine having that many going? 🤣) The equivalent clean air delivery rate from far-UV vastly exceeds anything possible with ventilation or filtration.
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The experimental data was recently confirmed through mathematical modeling showing you can achieve more than 100 eACH with far-uv.
To state this as clear as possible: there are no other technologies that are that effective.
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dx.doi.org/10.13140/RG.2.…
To state this as clear as possible: there are no other technologies that are that effective.
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dx.doi.org/10.13140/RG.2.…
Safety
What makes Far-UV special is that light between 200-230 nm is really bad at penetrating anything. The outer layer of your skin is the stratum corneum. It's dead tissue. It provides a protective layer to the living tissue underneath.
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What makes Far-UV special is that light between 200-230 nm is really bad at penetrating anything. The outer layer of your skin is the stratum corneum. It's dead tissue. It provides a protective layer to the living tissue underneath.
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Your eyes are also covered with a tear layer and far-UV is not good at penetrating that either. Think of your whole body with a protective covering 3-30 µm thick. Why is this important?
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colorado.edu/today/2021/10/…
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colorado.edu/today/2021/10/…
For other UV wavelengths, you cannot expose a room to UV light at doses effective at killing microbes when people are there. Because far-uv does not penetrate the outer layers well, your body can handle a high dose and you can irradiate the room with people there.
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For reference, most UVGI uses mercury lamps with 254 nm light. The exposure limit per day is 6 mJ/cm². For far-uv, the limit on the eyes is 160 mJ/cm²
and skin is 479 mJ/cm². A factor of 27 and 80 x respectively.
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and skin is 479 mJ/cm². A factor of 27 and 80 x respectively.
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https://twitter.com/joeyfox85/status/1608624087563399169?s=20&t=cSgke8qeguh4wdxdYbV8tg
So you can shine far-UV light in a room, it will be very effective at killing microbes and will have minimal effects on the occupants. This is what makes it unique and cannot be done with other UV wavelengths. You still need to remain within limits.
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https://twitter.com/joeyfox85/status/1608624087563399169?s=20&t=cSgke8qeguh4wdxdYbV8tg
Creating Far UV
KrCl excimer lamps give off light in the far-uv range primarily around 222 nm with some light outside the far-uv range. Many companies add a light filter to remove wavelengths outside the far-uv range.
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uvmedico.com/lamps/uv222-pe…
KrCl excimer lamps give off light in the far-uv range primarily around 222 nm with some light outside the far-uv range. Many companies add a light filter to remove wavelengths outside the far-uv range.
13/14
uvmedico.com/lamps/uv222-pe…
Lots of questions and comments. Here are some follow ups.
Far UV has a ton of potential, but there is still a lot we don’t know. There are many possible issues which I believe can be mitigated. Caution is still warranted at this time.
Far UV has a ton of potential, but there is still a lot we don’t know. There are many possible issues which I believe can be mitigated. Caution is still warranted at this time.
https://twitter.com/joeyfox85/status/1565735783255969795
For those looking to purchase, here are the manufacturers I know of. I have no conflicts of interest.
https://twitter.com/joeyfox85/status/1594147502076428289
For personal far uv, we don’t have evidence it is effective and I’m skeptical it does anything. I won’t use it until there is some proof (like the experiment in tweet 5 or mathematical modelling). It can be used for sterilizing surfaces, but that doesn’t help with COVID.
https://twitter.com/joeyfox85/status/1594780404745228291
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