Disinfection with Far-UV (222 nm Ultraviolet light) (2020) [pdf](boeing.com)

133 pointsby deegles3 lata temu141 comments

Disinfection with Far-UV (222 nm Ultraviolet light) (2020) [pdf]

https://www.boeing.com/confident-travel/downloads/CAP-3_Disinfection_with_Far-UV.pdf

147 comments

Nice to see this on HN, this is a big deal. I did research in 2021 to generate Far-UVC using nonlinear plasmonics.

The holy grail for this technology is a Far-UVC Diode. The guy who won the Nobel Prize for the blue LED (IIRC) is working with other physicists at UCSB to try and create said diode: https://www.news.ucsb.edu/2020/019949/uv-lights-way

If you want to learn more about Far-UVC itself (safety, etc), David Brenner is the real MVP: http://www.columbia.edu/~djb3/

throwaway20373 lata temu

Hat tip for the David Brenner link. The bottom of that page reads:

    Over the past six years, we have been working on a very exciting new approach to killing drug-resistant bacteria - superbugs- , as well as airborne viruses such as influenza, using a unique type of ultra-violet light. We have always known that ultraviolet light can efficiently kill all microbes, but conventional germicidal ultraviolet light is hazardous to our health, causing skin cancer and cataracts. We have identified a particular wavelength of UV light that has the best of both worlds - it's safe and it kills microbes - including superbugs.

While he doesn't say it directly, I guess he is talking about 222nm UV.

rngname223 lata temu

Wonder what it does to human health if the microbes on your skins surface are constantly exposed to Far-UV?

modestmc3 lata temu

Update: as a result of another comment, I stumbled into this: https://mdpi-res.com/d_attachment/ijms/ijms-23-09112/article...

My quick take on their experimental results is in the other comment, but in short it appears there will indeed be a trough of disillusionment somewhere down the line.

jefftk3 lata temu

Unless I'm misreading it, this paper looked at the effect on cells in isolation? But the reason we think 222nm is safe isn't that it has no effect on living cells, but that the living cells in our body are protected by a thin layer of dead cells that 222nm can't get through.

Here's the kind of paper I think is much more relevant, where they shined light into eyes directly: https://pubs.acs.org/doi/10.1021/acsphotonics.2c00041

Animats3 lata temu

> The holy grail for this technology is a Far-UVC Diode.

Right. Currently, 222nm lamps are gas-discharge tubes, and they cost far too much. There are fake 222nm LED lamps available online. There are also units that produce what Naomi Wu calls "homeopathic levels" of UV. Beware of scams.

If this is to go anywhere, a low-cost tester is needed. You can get a hand held UV spectrograph for about $3000, but that's more of a lab instrument. Something like a detector on a stick that lights up green for enough 222nm UV to be useful, and red for too much UV in dangerous parts of the spectrum.

One idea is to have a unit up near the ceiling that emits UV in a horizontal plane, so that air that makes it up to the ceiling gets sterilized. Convection, maybe with ceiling fan help, can move air through that region. But humans aren't up near the ceiling much, so they don't look into a UV source.

SexyCyborg3 lata temu

You can get 265-275nm LEDs- they are effective but you have to check them since there are constant scams.

https://twitter.com/RealSexyCyborg/status/154177301370350387...

You also have to dump a lot of heat so there's fan noise and Upper-Room GUV is already quite cheap so they aren't really game changers in that application- but they do work.

https://twitter.com/RealSexyCyborg/status/153744305018765722... https://twitter.com/RealSexyCyborg/status/153944537069847756...

222nm excimer lights are pretty costly per joule compared to 254-275nm given the 3,000hr or so lifespan of typical Chinese bulbs (although USHIO claims 10,000 is on the way) but from working with the factories they aren't quite as expensive as people think- the distributor markup is huge. You can also squeeze about 30% more out of them by switching to PTFE reflectors:

https://twitter.com/RealSexyCyborg/status/156236957519840051...

Best would be no reflector at all and pump as many joules into room air as we can with some air circulation, but right now we can only do that with unfiltered excimer lights- which aren't horrible but not something you'd want to sit with for several hours a day:

https://twitter.com/RealSexyCyborg/status/157656585826391244... https://twitter.com/RealSexyCyborg/status/159832965174278963...

Cylindrical 222nm cut filters would solve this but so far we can only get flat panes- and they are quite costly so building a square or triangular enclosure of filters costs more than you gain.

For what it's worth I make pretty extensive use of (filtered) 222nm- both portable and at home and I haven't caught COVID yet. Just an anecdote, but I've got no reason to stop using it- at least personally.

https://twitter.com/RealSexyCyborg/status/159942679977541222... https://twitter.com/RealSexyCyborg/status/159708372174773452... https://twitter.com/RealSexyCyborg/status/158850109792860160... https://twitter.com/RealSexyCyborg/status/161091221064529920...

The math on wearable Far-UVC didn't work out (exposure time is too short for the power, high power exceeds the TLV at that distance)- but it was a fun side project for a couple of days:

https://twitter.com/RealSexyCyborg/status/157297688745831219... https://twitter.com/RealSexyCyborg/status/158296013877611315...

As far as 222nm safety, I'm comfortable with it based on current data, used within recommended TLVs and have tested it on myself at length. But the one area I have concerns is folks with Lupus and other UV-sensitive immune disorders. It should be ok given that UVB seems to be the problem region, but we really have no information and I'd like some before any real widespread roll out of this technology.

https://twitter.com/RealSexyCyborg/status/155949983593741926...

Animats3 lata temu

> but from working with the factories they aren't quite as expensive as people think- the distributor markup is huge.

That is good to know. In the US these things are sold by high-markup "lifestyle" suppliers. Gas-discharge tubes are not inherently expensive, but the market is not yet large.

> A visible light filter that allows 222nm through. ... No blue UV death glow...

Yes. For long-term deployment that's needed.

galangalalgol3 lata temu

This still seems kinda scary. The scatter off the walls seems like it would be a problem for eyes or even skin over time. Would it generate ozone? What are the by-products of ionizing dust and what happens when you breath them?

MengerSponge3 lata temu

The good thing about far uvc is it isn't penetrating. It doesn't it make it through your your outermost cornea or epidermis layers.

Scatter is also negligible as long as its set up competently: reflectivity is very different for UV and visible light.

Ozone production certainly limits the maximum power that can be used, but as I understand it you don't need to crank anything close to max power to attenuate the airborne viral load.

ecesena3 lata temu

This is a recent interesting paper: https://doi.org/10.1111/php.13767

Showing effectiveness on surfaces, while remaining safe for humans.

I’m following closely the development, it’s still extremely costly to make a product but hopefully will see more adoption in the near future, starting at enterprise level. I have a device in my home, planning to permanently install it in the entrance where we leave shoes & co.

Feel free to dm me if you’re hacking in the space, happy to chat more.

blairanderson3 lata temu

I recently visited a national trade show for HVACR folks and found this company:

https://www.amazon.com/Blue-Tube-UV-Light/dp/B00D48XDO0/

Thought it might be applicable to computers, but realized that UV breaks-down PLASTICS as well, which is why you mostly find in ducting.

Very cool stuff if you're into clean/sterile living.

Note: Most of the dust in your home is comprised of human skin. Unless you've had an industrial vacuuming, other people's skin is moving around your house or gumming up the walls of your ducts. UV lights (and chemicals) are the only way to break that shit down.

throw0101c3 lata temu

> Very cool stuff if you're into clean/sterile living.

One concern I've heard about UV (and ionization) stuff is that you're adding 'active chemistry' into your ventilation system, which could possibly cause strange reactions you may not want.

Besides 'bugs' and dead skin, there are are VOCs and other chemicals that we use in our homes: how will those reaction? If these units are new and working properly, things may be fine, but how many homeowners will do (or have someone do) regular inspections/maintenance? Having this stuff in non-residential places may be fine because Facilities has a role in keeping HVAC working: regular people don't do that.

Having good filters (MERV ≥13) will get rid of most of stuff you don't want in a simpler fashion.

schiffern3 lata temu

HEPA gets all the hype, but if you can afford to recirculate the air for multiple passes (ie regular filtering, not a surgical theatre) then MERV-13 is the GOAT. It strikes a near perfect balance between particle interception efficiency and airflow volume.

Paradoxically, a 'more efficient' filter will generally achieves lower real-world performance (CADR) because the airflow drops so much.

The MERV rating are often hidden, instead you may need to look for numbers from a company-specific rating system like 3M's 'MPR 1900' or Home Depot's (yes, really) 'FPR 10.'[0]

(I almost don't want to include this last paragraph of info, because by sounding like an ad it will automatically 'taint' everything else, but fuck it....)

I find myself generally buying the 3M version (which is ~30% more expensive locally) which I observe has a much higher pleat count. That means more surface area (lifetime) and better pressure drop (airflow). By my math I come out ahead in cost per area of medium, which for me is a better metric than cost per filter.

[0] https://airfiltersdelivered.com/blogs/helpful-tips/merv-mpr-...

tempestn3 lata temu

Aprilaire 413 are our MERV 13 go-to. One other note not everyone may be aware of: if you have a central blower (aka furnace) that takes a standard 1" filter cartridge, it's usually not too expensive to add in a larger filter housing in the adjacent ducting. You just leave the default slot empty, or if you like, put a low-filtration backup filter in there. (Low filtration so as not to further restrict airflow.) So basically just because your existing unit only takes 1" filters doesn't mean you're stuck with that. Upgrade to 4" and you'll get better filtration and much longer filter lifespan.

schiffern3 lata temu

Great tip. I should compare the cost-per-area across 4" filters too. Often I'm just making a Corsi Box[0], so the filter thickness is unconstrained.

Anyone got recommendations for a reputable vendor online? Something other than BezosMart?

[0] https://cleanaircrew.org/box-fan-filters/

tempestn3 lata temu

It might be a bit more challenging to make one of those with 4" filters, but yeah, worth a look at least. The other reason I like it is that our furnace is in the crawlspace, so having to get down there less often to change the filters is a pretty significant benefit. I'd do it even if the total cost were equal or higher.

JoshTriplett3 lata temu

> put a low-filtration backup filter in there

It isn't just a backup; you want it there before the expensive fine-grained filter, to catch the big stuff and extend the life of the more expensive filter.

tempestn3 lata temu

That's not always feasible, as the built-in filter is usually integrated with the air handler. The add-on will generally have to be in the inlet ducting, so it will come first. I'm not sure that approach would even reduce cost though; much of the benefit of the large filter is that it has way more surface area, and so it lasts longer before restricting airflow too much. If you put a 1" filter in front of it, now you'll have two filters you need to replace regularly. You might preserve the life of the larger filter a bit, but not enough to make up for the cost of the whole extra filter. So I think I'd prefer to either just use a 4" alone (which is what we indeed do), or have the 1" as a backup, and basically use its condition to test whether anything significant is getting past the main filter. It would very rarely need to be replaced, as the primary filter should be catching everything.

schiffern3 lata temu

For a prefilter I sometimes wedge in a fiberglass "stick filter" to catch larger dust and pet hair. At service time I vacuum it off (or just bang it off in the trash) and reuse.

I wouldn't use a prefilter with any real pressure drop thought. Why not? Well...

In theory a two-stage filter is ideal, because you can cycle the filters through: swap the (mostly clean) post-filter over to the pre-filter during filter changes, optimizing both filtration level and using the full capacity of each consumable filter element. This is the procedure when changing the ISS water filters, incidentally.

There's a downside, of course...

Essentially it's the same as series and parallel resistors, so for two filter stages in series (to achieve the same rated pressure drop) you need double the rated size for each of the stages, therefore 4x the total filter area and size. In practice, nobody really wants to install that in their basement.

Some of the Chinese positive pressure systems have seemingly the ultimate low-consumables design: a washable stainless prefilter, washable electrostatic filter, two stages (supports cycling) of HEPA filter, and last a refillable granular activated carbon stage. Spent activated carbon could be used as a soil amendment, or returned to a local facility for regeneration into new activated carbon.

Very low consumables, but very costly up-front.

wnevets3 lata temu

Wouldn't UV-light in ducting generate ozone? Even relatively small amounts of ozone can be harmful.

> When inhaled, ozone can damage the lungs. Relatively low amounts can cause chest pain, coughing, shortness of breath and throat irritation. [0]

[0] https://www.epa.gov/indoor-air-quality-iaq/ozone-generators-...

Eisenstein3 lata temu

Ozone is produced at 185nm. Standard germicidal UV-C lights are ~250nm. The issue is that some germicidal bulbs do not filter out the lower wavelengths and thus produce ozone (sometimes on purpose since ozone is also germicidal). See [0].

[0] https://en.wikipedia.org/wiki/Ultraviolet_germicidal_irradia...

jefftk3 lata temu

> Standard germicidal UV-C lights are ~250nm.

The article is about KrCl 222-nm lights, which people want because they're safe [1] to shine on people, unlike Hg 254-nm lights.

[1] Probably -- I'd like to seem some specific additional experiments before widespread deployment.

lazide3 lata temu

222nm is not safe to shine on anyone! It will definitely cause skin cancer.

254nm is also not safe.

254nm destroys ozone, interestingly.

240nm and smaller (160nm being the highest producing freq.) produce ozone.

[https://onlinelibrary.wiley.com/doi/full/10.1111/php.13391]

bsder3 lata temu

> 222nm is not safe to shine on anyone! It will definitely cause skin cancer.

The whole point of using 222nm is that it doesn't cause effects on either the eyes or the skin. Consequently, you can use it at higher concentrations without worrying about the leakage.

The issue, as I understand it, is simply that we don't have a decent LED monochomatic source. All of the currently available sources have broad spectrums that have to be filtered out.

hedora3 lata temu

The claim that 222nm is an effective disinfectant seems to directly contradict the claim that it cannot penetrate skin. In particular, if it bounces off dead skin cells, and the environment contains dust, how can it possibly kill things on the dark side of the dust particles?

On top of that, reasonable disinfectant timeframes are a few minutes to a few hours, tops. Safety timeframes for human exposures need to be measured in decades if this technology catches on. Claims that lethal dosages of 222nm will penetrate typical glops of pathogens in the environment in seconds, but that cancer causing dosages will not penetrate human skin over years are extraordinary.

Extraordinary claims require extraordinary evidence. Are there long term safety trials for this technology? The article claims “reduced damage” in the abstract, implying routine 222 nm exposure is unsafe.

bsder3 lata temu

> The claim that 222nm is an effective disinfectant seems to directly contradict the claim that it cannot penetrate skin. In particular, if it bounces off dead skin cells, and the environment contains dust, how can it possibly kill things on the dark side of the dust particles?

It penetrates single cell walls but nothing deeper.

People are mostly interested in 222nm for doing things like sterilizing air circulation and handheld wands. You can put a very high flux without worrying about accidentally exposing someone to a hazardous level of UV light.

People aren't trying to sterilize skin directly (as far as I know), but, even there, it might help healthcare workers. Washing your hands or coating it with alcohol is nasty over time. Being able to hold your hands in a device for 15 seconds and sterilize it rather than having to dump alcohol on them could be an improvement.

hedora3 lata temu

"Airborne" viruses are almost always traveling in protective droplets of fluids, sloughed cells, etc, etc. Direct contact with air kills them. So, how does the UV get inside the droplet so that it can reach the pathogen?

iggldiggl3 lata temu

Apart from the human safety factor, I'm also curious what it does to other stuff typically found in houses? Even if you were to run the disinfection cycle only while the room is unoccupied, it still affects everything else in the room.

So is the combination of 222 nm + exposure times required for disinfection still enough to cause noticeable bleaching of paints, aging of plastics, etc. etc. over time?

scotty793 lata temu

It's basically because viruses and harmful bacteria are smaller than our dead skin layer. So the light gets into them and destroys their DNA/RNA.

harvie3 lata temu

but viruses and bacteria are probably never traveling alone. imagine someone sneezing on table. they will be embeded in pieces of dead skin or tiny droplets of phlegm, saliva, etc... in the linked article they are using it to disinfect surfaces in passenger aircraft. unless it can penetrate a bit, i don't see how it can be effective.

also viruses (eg. HIV, Coronavirii,...) are often killed by oxygen in air, dry out or die in other ways when not floating in bodily fluids.

jefftk3 lata temu

The light doesn't need to kill 100% of pathogens to be effective at decreasing risk. I agree that if the pathogen is on a table but under a protective layer the levels of UVC we're talking about aren't going to do anything to it. But the main concern is with airborne viruses which mostly aren't very protected.

lightedman3 lata temu

Sadly, not even LEDs are truly monochromatic and typically have a ~20nm spread on either side of the peak. They also exhibit drift in wavelength peak. This is seen at my job, where I run the UV testing and production.

scotty793 lata temu

I don't think it needs to be monochromatic. If the longest wavelength is 222nm, other penetrate skin even less.

jefftk3 lata temu

The longest wavelength isn't 222, that's the peak wavelength.

KrCl excimer lamps produce a relatively narrow spectrum as is: https://pubs.acs.org/doi/10.1021/acsphotonics.2c00041

If it turns out we need it to be even narrower, we could put filters on them.

jefftk3 lata temu

I don't see anything in your link about 222nm causing skin cancer? It's short enough that it shouldn't be getting through the outermost layer of skin, which is dead.

lazide3 lata temu

Welders have plenty of experience to contradict it. UV-C is usually blocked by the atmosphere, and most people don't get exposed to it directly - so it rarely comes up. But if you're sitting next to a UV-C generator, don't.

It cleaves DNA the same as UV-B, and there is no reason to think it isn't cancer causing. There are a number of areas that can get exposed that have very thin epidermis, or none at all (eyes), though eyes would get retinal keratosis not cancer.

That said, hopefully no one is spending enough time close to a high enough power UV-C source for this to REALLY be a problem.

Welding Cite - [https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5640727/]

Notably, while having a higher skin cancer risk despite being inside a lot (shop welders, not shipyard welders), the vast majority of welders in that sampled population will have been wearing heavy protective clothing continuously. There was a noticeable increase in risk of skin cancer on the neck, which is one of the few areas that is not always adequately covered.

Anecdotally, I knew folks who didn't wear proper full coverage PPE when welding and welded a lot (auto body repair in one case, farm equipment repair in another), and both died in their early 40's from multiple malignant melanomas. One of them, it was 10+ all at once, and he died in less than a year. No one was surprised, unfortunately. They were ALWAYS sunburned from it, and they didn't spend a huge amount of time outside otherwise. That is a pretty broad spectrum source though.

UV-C As Potentially Mutagenic/Causing Damage not caught by normal replication suppression mechanisms - [https://pubmed.ncbi.nlm.nih.gov/9951833/]

UV-C will also have no problem converting all sorts of organic chemicals into interesting, and often more toxic versions (albeit killing any organisms relying on their original structure in the process), same as UV-B or UV-A.

the84723 lata temu

welding light is broad-spectrum, so it's not relevant when comparing to a narrow-peak light source.

> UV-C As Potentially Mutagenic/Causing Damage not caught by normal replication suppression mechanisms - [https://pubmed.ncbi.nlm.nih.gov/9951833/]

p53-/- human keratinocyte cell line means that those were in vitro experiments which don't account for the wavelength-dependent penetration depth, which is the point of discussion here.

jefftk3 lata temu

None of your links are about 222nm; they're all about longer wavelengths or mixes that include longer wavelengths.

daniel_reetz3 lata temu

Let's be clear here. Nothing outside of some extremely filtered high end equipment is producing exactly and only 222nm light, and no cancer study is isolating exactly and only 222nm light. Except in extreme cases all light sources have some bandwidth. Most UV generators produce tens to hundreds of nm of bandwidth. A common MIG or TIG welder produces plenty of 222nm light in a broad distribution* of UV. UV lamps for curing applications have used arcs to generate deep UV for ages. Lack of a particular study for a particular 1nm band is not a meaningful signal.

*Source: https://www.ehime-iinet.or.jp/ehime_e/corp/toyo/ronbun/image...

jefftk3 lata temu

I agree welding is very broad spectrum, including both 222-nm and many other frequencies, and also dangerous. But these KrCl excimer 222-nm products generate light through a completely different mechanism and produce a far narrower spectrum. See https://pubs.acs.org/doi/10.1021/acsphotonics.2c00041 and specifically this chart https://pubs.acs.org/cms/10.1021/acsphotonics.2c00041/asset/...

We do know a lot about how dangerous different frequencies are, and when you combine the "risk to humans" curve with the "emissions by wavelength" curve you get very low risk.

I do still think we should run additional experiments here before rolling this out broadly for hours-a-day usage, but from what we know so far it looks very good.

daniel_reetz3 lata temu

Perhaps 222nm is absorbed primarily by dead skin cells - but why is skin the only tissue mentioned? It says nothing about damage to corneal and conjunctival tissues. Eye damage is a major hazard for humans with UV light in particular. "Very low risk" simply doesn't track. "Reduced risk" might.

jefftk3 lata temu

Eyes, like skin, have a layer of dead cells, and sufficiently short wavelengths can't get through. If you shine enough 222-nm into eyes they'll get dry and uncomfortable, but we're talking about much lower levels.

Here's an example of some of the research here, where they shined 222 nm vs 254 nm into rat eyes and looked for corneal damage. While 254 had some harmful effects 222 was fine: https://www.tandfonline.com/doi/abs/10.1080/10715762.2019.16...

red-iron-pine3 lata temu

Anecdote of one but...

Have an uncle who is / was (recently retired) a welder. He worked everywhere, did all sorts of welding, and even got certified to do underwater stuff -- which he did for 2 years and GTFO out of as soon as he made enough $$$$

He got skin cancer on his next and on his right elbow. Cuz that's where the gloves and other PPE clothing had gaps, esp. when he leaned certain ways or use his right hand to move the torch.

amluto3 lata temu

And yet Far-UVC seems quite safe for people.

Presumably what’s going on is that longer wavelength UVC from welding is extremely dangerous.

wnevets3 lata temu

>Ozone is produced at 185nm

Where did you find that 185nm number? Everything I see on google says ~250nm, not to mention the original post is about 222nm UV.

lazide3 lata temu

~ 250nm actually destroys ozone.

Smaller than 240nm creates it, to various degrees, with the ideal frequency being 160nm. 185nm is 'produces a noticeable amount'.

[https://onlinelibrary.wiley.com/doi/full/10.1111/php.13391]

wnevets3 lata temu

So the 254nm referenced by the linked product could actually reduce the amount ozone in the air? Assuming of course it wasn't also emitting lower frequencies.

lazide3 lata temu

Yes, but.... if you look at the paper, most of these lamps have some degree of lower wavelength light production. Some of them mitigate it through the glass they use, some of them make it worse. There is no good or easy way to tell. :(

etiam3 lata temu

I'm certainly not a physical chemist, but at that sort of energy levels wouldn't it rather be liable to drive the gas mix towards some sort of equilibrium?

I'd imagine it breaks down molecular oxygen (some of which goes on to form ozone), and it breaks down ozone (some of which goes on to re-form ozone).

At any rate, that seems like altogether too radical to be desirable near living creatures whose well-being one cares for.

lazide3 lata temu

Yup, and the paper I linked has some detailed analysis of some scenarios. In some cases (particularly bad mercury vapor lamps), it can produce dangerously high ozone levels (50x EPA safe working limits).

In others, no foreseeable issues even if run 24x7.

So, uh, maybe don’t buy cheapo units off Amazon unless you have some way to see/test what they’re doing.

jefftk3 lata temu

The linked product peaks at 222nm and is filtered to exclude longer wavelengths. It's being compared to Mercury vapor lamps that peak at 254nm.

wnevets3 lata temu

The blue tube product linked in the original comment I replied to says 254nm.

https://www.amazon.com/Blue-Tube-UV-Light/dp/B00D48XDO0/

jefftk3 lata temu

Whoops, sorry! I was trying to talk about the linked article, and missed that the comment had brought in a different product.

RetpolineDrama3 lata temu

Carrier at least claims their UV upgrade does not produce ozone. Not sure how accurate that is though.

KennyBlanken3 lata temu

You'll note the installation location - in the evaporator unit. It's to reduce mold growth in the evaporator unit, not sterilize air.

UV units intended for installation in return or supply ducts are snake oil. A waste of electricity and money (the bulbs have a pretty finite lifespan.) The velocity of air in most ducts is such that anything flying by wouldn't be sterilized, and you can just install a large air filter (like the Aprilair 413 others have mentioned) and it'll bring a lot more benefits to the table, namely much better reduction of dust.

The greatest problem with indoor air quality is offgassing of VOCs and other pollutants from construction materials, furniture, electronics, etc.

If you want the best indoor air quality: install a large filter like the Aprilair or some equivalent, an air exchange device, and if you have a gas stove/oven, switch that to electric.

lightedman3 lata temu

"UV units intended for installation in return or supply ducts are snake oil. A waste of electricity and money (the bulbs have a pretty finite lifespan.) The velocity of air in most ducts is such that anything flying by wouldn't be sterilized,"

If you just do the simple thing and point the lights in a self-facing ring in the duct, no, they will not work. The trick is to beam the light down the incoming pathway to drastically-increase the exposure time. Clean reflective surfaces in the ducting to even out the photon flux density will greatly help with this.

eutectic3 lata temu

It's a myth that household dust is mostly skin cells. It only makes up a small percentage.

thedougd3 lata temu

I believe these are for keeping your evaporator coils clean and funk free rather than cleaning your air. The air movies past it much too quickly.

purpleblue3 lata temu

At the beginning of the pandemic, I read about UVC light and purchased a UVC light bulb before they ran out online. I used it to sterilize my N95 masks which were impossible to find, and all the research I did showed that you could do this 20+ times without affecting air flow or filtration of the mask. I even found studies that talked about how to use it to disinfect flu virus so I used those as a guideline as to how long I should expose the masks. I even went so far as to buy ajar and tested that the UVC light at least killed bacteria as advertised. I know viruses are much tinier and there's no way to test for the virus but at least I knew it was working as advertised for bacteria.

Of course all this ended up being useless, but it was a fun project during the pandemic.

smileysteve3 lata temu

similar, i read something about uv-c in 2019; and also how washing machines most active cleaning is from water (they don't kill things well), so had added a uv-c light to "treat" my laundry.

mr_toad3 lata temu

The water and soap remove dirt and grease that bacteria feeds on and lives in. You don’t need to sterilise your clothes, you just need to stop them being a breeding ground.

maximilianburke3 lata temu

One of the most driven* and intelligent people I have ever had the opportunity to work with (Saimir Sulaj) left my company to found a startup that's building far UV disinfection devices:

https://www.uvxinc.com/

*I mean, it requires a certain kind of stubborn determination to do a hardware startup, and I hope he's crushing it.

com2kid3 lata temu

Unfortunate it is one of those "inquire now" things, if there was a "buy now" link I'd pick a few up right away.

sethikunal3 lata temu

donsupreme3 lata temu

I am curious if the ambience air can be too "sterile", that we will come to find out there are some good microbes in the air that is beneficial to our health.

Auracle3 lata temu

Well, keep in mind humans didn’t evolve to live in big cities and children in daycare and schools. I would think that the past 500 years or so the amount of illness each person suffers has gone up exponentially.

Viruses are also linked to all sorts of nasty outcomes like Alzheimer’s, cancer, etc. I doubt we’ll have any means to knock transmission back a ton anytime soon but it’d be nice to do what we can.

eutectic3 lata temu

I think it's extremely unlikely that rates of illness have gone up.

seszett3 lata temu

I think at least the profile of illnesses must have changed.

I spent a year on a rather isolated base on an island, with about 50 other people. Hygiene was certainly not as good as it is here in the civilised world as we often didn't have running water, ate wild meat that had simply been stored in the cold outside for days, food products with an expiration date a few years in the past, etc, and we just didn't get sick. We got sick when the supply ship came, though. It wasn't Antarctica either, the conditions are mostly similar to Northern Europe, not so different from Brittany.

I think the situation is quite similar to how humans lived for a long time, in small groups with only occasional contact with strangers, and in these conditions I'm sure infectious disease was much less common than it is now.

Of course disease did exist, but I think it would mostly have been diseases brought by insects or other vectors, not as much things like the flu or the common cold.

jwuphysics3 lata temu

As someone who is unaware of any relevant literature on the subject, I'd love to hone my intuitions a bit. Could you say more about your line of reasoning?

mrtesthah3 lata temu

Well, because we have things like clean water and sanitary preparation of food, we can avoid things like typhoid fever, cholera, ecoli, and all manner of parasites.

qbasic_forever3 lata temu

We also have jets and international air travel that can take a patient zero anywhere in the world and around any people in a matter of hours (well before they're too sick to know not to be traveling).

With the Spanish flu in 1918 it took months for it to get around, mostly through rail and steam ships. With COVID-19 we saw some variants explode around the entire globe in a matter of _weeks_.

refurb3 lata temu

I would think that the past 500 years or so the amount of illness each person suffers has gone up exponentially.

It's actually the exact opposite? Improved hygiene and vaccination means rates of illness have dropped.

qbasic_forever3 lata temu

Our body would have evolved to keep whatever these 'good' microbes are in and near our lungs, much like it does for our intestines and digestive system. The lack of this system, and the evolution of things like hair and mucous in our nose to filter and trap foreign objects is a pretty good hint that our body doesn't want anything except our clean atmosphere in our lungs.

malfist3 lata temu

Fair, but your body also does away with things it's not using. An inactive immune system for too sterile environments may result in not being able to protect yourself in less sterile environments, or the immune system finding uses for itself, i.e. an autoimmune disease like allergies.

qbasic_forever3 lata temu

The immune system is not a muscle--you don't need to keep exposing yourself to pathogens. Think how ridiculous that sounds--are you going to go get rabies, ebola, HIV, brain eating bacteria, etc. to be 'healthy'?

mr_toad3 lata temu

The whole point of a vaccine is to expose the immune system to an antigen.

qbasic_forever3 lata temu

No, you're exposing a harmless or safe part of an antigen to stimulate memory B and T cell immune response in the future.

Rawdogging unfiltered air with true COVID or other bad virons will expose you to a potentially harmful virus--millions of people have been killed and many more disabled from it so far. You have no way of knowing if you will join their fate and are just rolling the dice.

ajmurmann3 lata temu

Would you, by the same logic, suggest that we filter drinking water less?

wkat42423 lata temu

That's a good example of training the immune system actually..

Go to southeast Asia where drinking water isn't so great. Drink it as a tourist and you'll spend a few days running to the toilet. But a native will drink it just fine as they're exposed to it all the time and their immune system has learned to deal with it.

Low level exposure is good for that, you will find germs everywhere, not enough to make you sick but enough to give your immune system a heads-up for when it does come across a high level source of them like a contagious carrier.

Eisenstein3 lata temu

They also do end up getting serious diseases. There is no way to filter 'just a little to get enough of the bad stuff out but keep a tiny bit in' and ensure safety.

If you really believed this you would tell your surgeon not to bother wearing gloves or wash hands because you want to ensure your immune system is functioning ideally,

wkat42423 lata temu

No, this is because a surgeon actually works with carriers of infectious diseases. So a direct source of these, rather than a passing encounter. And vulnerable patients (open wounds etc) of course.

When the surgeon goes home on the metro he doesn't wear gloves either. Or a mask in many cases.

Of course living in a sterile environment works but the problem is that you will then have to do it all the time everywhere. Otherwise the first time you're out of that environment your immune system will have to catch up on everything. And there's a whole spectrum in between. Perfect "safety" is not possible while having an actual life.

The question is, does the covid pandemic indicate we should move towards the more sterile side of that spectrum? I personally don't think so, on the contrary. If you see the isolationist tactic employed by China it has been far less effective at getting the situation over with than our approach in the west. We were enjoying our lives for a year while the Chinese were still brutally locked up.

In the case of Southeast Asia, just getting used to the water is far more easily achieved than fixing it everywhere due to the high cost of a good water system. Some people get ill but life always carries risk. And for foreigners there's always bottled water. In our case we make a different tradeoff.

But training the immune system against common threats by exposing it to low level sources is really a thing. If it couldn't do that we would have been extinct millennia ago :) Because threats appear much faster than evolution can cope with them.

Eisenstein3 lata temu

> In the case of Southeast Asia, just getting used to the water is far more easily achieved than fixing it everywhere due to the high cost of a good water system. Some people get ill but life always carries risk. And for foreigners there's always bottled water. In our case we make a different tradeoff.

'Southeast Asia' doesn't make a trade-off because they analyzed the data and came to the conclusion that their population is better off with half-filtered water, they do it because they are poor and have bad infrastructure. Would you like their water supply so you can get your immune system trained? While at it maybe start eating unrefrigerated food. My friend from Africa did that growing up and has an iron stomach -- it sure does work (too bad about all the kids who died though because they got unlucky).

The problem isn't 'it doesn't work', the problem is 'you can't just get rid of the awful bad ones and leave the kinda bad ones. Either you do it or you don't.

This is why your type of argument is terrible.

wkat42423 lata temu

It's just that I draw the line at "good enough" with where we are now.

I'm ok with the risk and I don't want to go everywhere masked (which I find really horrible for historical trauma reasons) or bother with ventilation and sterilisation stuff. I will never do that kind of stuff willingly.

If anything covid told me it's better not to be too fussy because it's over quickly (unlike China which really tried to kill it at all costs).

But when people say the immune system can't be trained by exposure I just have to disagree.

Eisenstein3 lata temu

That isn't what this thread is about. You tagged on to an argument that 'we need to keep our immune systems active', which is bullshit because getting cholera or covid is not healthy and keeping environments like HVAC/vent systems as sterile as possible (for instance using UVC) is important so that COVID doesn't blow into peoples faces in the unnatural environment of people crammed into small enclosed spaces.

wkat42423 lata temu

I think it is important to 'see' a little bit of covid all the time so the immune system knows it's still a thing and keep making antibodies. And the cost of those HVAC sterilisations will of course be paid by all of us (customers of venues, transport etc).

But anyway your mind is set and so is mine so there is no point in continuing.

Eisenstein3 lata temu

> I think it is important to 'see' a little bit of covid all the time so the immune system knows it's still a thing and keep making antibodies.

So you are arguing because you feel like it is correct, based on nothing more than your own intuition.

> And the cost of those HVAC sterilisations will of course be paid by all of us (customers of venues, transport etc).

Are you willing to give up your nice clean water and get some 'southeastern asian' water to save a few cents? I mean, who cares how many people die from it, cause life is risky eh?

jefftk3 lata temu

Dereck Lowe ("In the Pipeline") has a good article on germicidal 222-nm: https://www.science.org/content/blog-post/two-twenty-two

EGreg3 lata temu

Hi everyone. I had this idea two years ago, and made an entire website and video about it: https://uvspinner.com/

Tried to get the NYC mayor's office interested, but they just pawned me off to a black hole of submitting forms that no one reads.

If anyone still wants to do it, shoot me an email, username is greg with the domain "qbix.com" or add me on Facebook

joezydeco3 lata temu

UV will break down a lot of plastics, especially if stabilizers are not added. I'm curious why the study didn't mention this at all. How long can that bathroom hold out?

jefftk3 lata temu

If you're Boeing considering building it into planes it seems like you're in a great position for choosing UV-compatible materials.

(Compared to the more normal situation of someone retrofitting an office, bar, or other normal space with 222-nm lighting.)

bilsbie3 lata temu

Remember when we needed germs to exercise our immune systems? Remember immune systems?

2muchcoffeeman3 lata temu

I think there is a big difference between exercising your immune system and creating a Petri dish for air borne diseases. If COVID has taught us anything, it’s that ventilation in many buildings sucks big time. We need to either improve ventilation, or start killing viruses.

I mean, if you’re going to go the naturalistic angle, then what’s natural about squashing people into buildings with poor air flow?

ChrisMarshallNY3 lata temu

> ventilation in many buildings sucks

We've known that for a long time[0]. I have friends that are plumbers and HVAC people, that have to do strange stuff, by law.

[0] https://www.cdc.gov/legionella/index.html

eutectic3 lata temu

Can you expand on this enigmatic comment?

ChrisMarshallNY3 lata temu

Just that Legionnaire's Disease has caused a whole lot of laws and codes to be created. Things like that weird gap under industrial sinks.

ragazzina3 lata temu

Are you sure the gap under the sink is due to Legionnaire's Disease? I think it's just not to contaminate the sink in case of backflow.

ChrisMarshallNY3 lata temu

According to my industrial plumber friend (over 40 years), the distance is set by law, and it is specifically for Legionnaire's Disease. Whole bunch of other stuff, too.

He worked on skyscrapers all over NYC.

marcosdumay3 lata temu

Or maybe the 20th century increase in allergies was caused by the sheer amount of bad stuff we created, or maybe it's because of the sheer concentration of badly ventilated environments where hundreds of people pass through every day.

AFAIK, there is no good evidence about any of those hypothesis, and weak ones for them all.

deegles3 lata temu

let me know how your exercise with avian flu, yellow fever, HIV, ebola, hepatitis, etc etc etc goes.

guntherhermann3 lata temu

1) Cool it with the snark

2) Ebola, Yellow Fever, HIV & Hepatitis aren't airborne, so probably wouldn't be the kind of viruses that the parent is talking about

deegles3 lata temu

They'll just have to chime in and clarify which pathogens they meant.

I was snarky because the idea of "exercising the immune system" is misinformation and used by "immunity debt" proponents.

RenThraysk3 lata temu

It's a shame we haven't figured out to make efficient Far-UV leds. The performance drops off a cliff once start to get below 265nm (IIRC)

lightedman3 lata temu

The performance drops off a cliff to tungsten-lamp levels starting in the UVB (290-310nm) range. We're still looking at state of the art at barely 3% efficiency for that and UVC.

jbm3 lata temu

The Canadian government has a page that includes some information about the effects of Far-UV light against Covid-19.

https://www.canada.ca/en/public-health/services/diseases/201...

> A whole room UV simulation demonstrated a far UV-C lamp (207-222 nm) could further reduce SARS-CoV-2 by 50-85% compared to ventilation alone and with both far UV-C and high ventilation the SARS-CoV-2 viral count was reduced by 90% in 6 minutes and 99% in 11.5 minutes Footnote 5.

I wonder if this is something that I could add to my pre-existing home ventilation system; no concerns at all about skin exposure (which doesn't seem to be an actual issue based on this Boeing paper), and it shouldn't be so hard.

* I found this (https://faruv.com/) but I don't know how reliable they are.

That said, if this really was that effective, I don't understand how viruses and bacteria are able to survive outside with our fusion-powered UV ray generator in the sky.

-edit- * I feel dumb, here it is at the end of the summary. Looks like Boeing is working w/ faruv.

> Boeing recently entered into patent and technology licenses with Healthe® Inc. and FarUV Technologies. Under these licenses, both companies will produce and distribute a commercial Far-UV 222 nm mobile wand, helping airlines and potentially others reduce the impact of the coronavirus pandemic.

com2kid3 lata temu

> That said, if this really was that effective, I don't understand how viruses and bacteria are able to survive outside with our fusion-powered UV ray generator in the sky.

There is a reason that even during the height of the pandemic, that outdoor events were not a large source of transmission.

People going into bars or houses after marching/protesting/partying were a problem, but standing around in the sunshine, even in a reasonably dense crowd, wasn't ever really a problem. (AFAIK, I remember news articles going "well that didn't turn out as bad as we all thought it would")

Krssst3 lata temu

If this was the reason, wouldn't it mean that we should be careful outside during the night?

hedgehog3 lata temu

There are a few different ways I've read about far UV being deployed, one of the interesting ones is illuminating the upper few feet of a room. Exhaled breath tends to rise so apparently doing just the top of the room is more effective than you might expect. I hope this pans out to be effective, it would be a way to improve air quality without adding more noise to the space.

Edit: The article's claim is that because far UV is absorbed in the upper atmosphere there's not really any evolutionary pressure for organisms to develop protection. Larger organisms just happen to be protected by virtue of our size.

ericbarrett3 lata temu

UV-C is absorbed by the ozone layer.

samstave3 lata temu

Wouldnt it be best to create a modular off-the-shelf instalable, positive pressure man-trap (extendable to walkable tunnel length, in the entrances to large public areas (stadiums, airports, trains, malls, etc)

turn that wand into wall panels and let people walk through it - just like any other clean-room-style man-trap?

https://i.imgur.com/8dMGNjN.gif

purpleblue3 lata temu

The wand will be useless unless they hold it above the area for 30+ seconds, which probably won't happen. Or unless the light is extremely intense which sounds dangerous.

lightedman3 lata temu

I tested this at work. 222nm, 265nm, 275nm, 290nm. Petri dishes colonized with human underarm flora were prepared, closed, then incubated for an hour at 80F. tested times were 30 seconds, 60 seconds, 2 minutes, 3 minutes, 5 minutes.

222nm doesn't take even 30 seconds to wipe things out. Every dish was totally clean.

265nm needed about 2 minutes to sterilize.

275nm almost got the job done at 3 minutes and had the 5 minute dish totally clean.

290nm was frankly pathetic. All of the dishes survived with barely-decreasing colony count across increasing times. I estimate it'd take an hour of exposure to clean the dish.

londons_explore3 lata temu

We need more studies, or maybe metastudies, that compare the germicidal benefits of UV lamps with the health disadvantages (skin cancer, ozone).

It seems that there is consensus on both effects, but I can't find anything conclusive that allows the scale of the effects to be measured sufficiently to do a benefit/cost analysis for each type of light spectrum and usecase.

modestmc3 lata temu

Far-UVC (~205-222 nm) light can’t penetrate cell walls and thus does not risk DNA damage.

However, our skin heavily depends on friendly bacteria to do useful things. One concern that I have yet to see research testing is the impact of extended Far-UVC exposure on these microbial populations.

thfuran3 lata temu

Human cells don't have cell walls.

modestmc3 lata temu

My apologies, the membrane. I went and dug more into this to brush up on the exact specifics and the exact conclusion of the research was that less than 5% of the intensity of the light reached the nuclear envelope, thus avoiding DNA damage. This is the original study: https://ieeexplore.ieee.org/abstract/document/1341520/

However, while I was trying to find the specifics on the DNA damage, I found this: https://mdpi-res.com/d_attachment/ijms/ijms-23-09112/article...

My only grief with this article is the conclusion they draw from the yH2AX staining. I can see several possible reasons for observing the higher proportion of cells with it.

Other than that, the paper raises a boatload of serious points and definitely observes negatively impacted cellular function. I still think FarUVC has incredible potential but just like cellphone towers the exact specifics to interact with it safely need serious further study.

lazide3 lata temu

Skin cancer is easy to prevent by not allowing the light to shine directly on anyones skin, and using non-UV reflective enclosures.

Ozone is already a known and easily tested quantity, and generally only happens at 240nm and lower wavelengths. So 222 as listed might produce some, but doesn't seem optimal (180nm seems better).

Found a paper - seems likely that is the case [https://onlinelibrary.wiley.com/doi/full/10.1111/php.13391]

Note scale on the first graph.

edit: ah hah, but many of these lamps have defects that can result in higher freq. light emission and high ozone production! See later parts of the paper.

[deleted]3 lata temu

apienx3 lata temu

This group's notorious for shining UV at fashionable pathogens. https://www.nature.com/articles/s41598-020-67211-2

refurb3 lata temu

https://www.biorxiv.org/content/10.1101/2022.02.22.481471v1....

However, cells exposed to 222-nm far UVC presented the highest degree of DNA damage as evidenced by yH2AX staining. Globally, these cells presented transcriptional changes in cell cycle and senescence pathways. Thus, the introduction of 222-nm far UVC lamps for disinfection purposes should be carefully considered and designed with the inherent dangers involved.

Maursault3 lata temu

> recently published studies have demonstrated that UV light at 222nm has the same germicidal capabilities of 254nm light without damaging skin or eyes.

222nm may have the same capabilities, but not the same efficacy and efficiency as 254nm (or 185nm, the germicidal action if which is it creates ozone, which does the disinefecting). Still, if it works but just takes longer without the sunburn and blindness, whether by proximity to 254nm such that some 254nm is still present, and/or by proximity to 185nm such that ozone is still created, well, ok.

hedgehog3 lata temu

According to the linked article: "While the effects on live tissue are diminished, Far-UV (222 nm light being the most prevalent) has increased efficacy for killing bacteria and viruses."

Maursault3 lata temu

That's misleading, increased efficacy as opposed to what? A control? It's not more than 254nm, which has been long proven, in repeated studies, to be the most efficient germicidal wavelength, decreasing in near wavelengths depending on how close they are to 254nm. 222nm is only 32nm of wavelength difference to 254nm, and I'll wager that even 238nm is more efficient than 222nm, but maybe 238nm burns skin. 222nm is nearly half way between 185nm and 254nm, so it will have some of the germicidal effects of both wavelengths, but it won't be more than either 185nm or 254nm. But it may be enough, and if it doesn't hurt people, then kudoes.

scythe3 lata temu

>254 nm

... which just happens to be exactly the second spectral line of a low-pressure mercury-vapor lamp. Actually 253.7. The other line is 184.5. Are you sure that the study you read isn't just reporting this wavelength as ideal because we have a convenient source of it? Efficient far-UV sources tend to be few and far between. It would be an awfully big coincidence if the two major spectral lines of an Hg plasma just happen to be the two ideal wavelengths for disinfection.

FWIW, zinc vapor has a persistent line at 214 nm, but I've never heard of this being applied in a commercial bulb. Other relevant possibilities are all toxic.

Maursault3 lata temu

> Are you sure that the study you read isn't just reporting this wavelength as ideal because we have a convenient source of it?

Studies, and yes. Mercury vapor's spectral emission is just a happy coincidence and why mercury vapor lamps are used for germicidal applications. The germicidal LED's they make are 255nm. But 254nm, not 255nm, not 253.7nm, is the most efficient wavelength for germicidal applications, in that it kills the most bugs the fastest. Please don't make me dig up the studies, please find them yourself, there are plenty, and it'll mean more to you.

viraptor3 lata temu

Just read the article. It's "compared with 254 nm light". Both sentences are in the abstract.

scotty793 lata temu

I think it's already used in some places: https://www.reddit.com/r/ZeroCovidCommunity/comments/10kbkhz...

[deleted]3 lata temu

ajmurmann3 lata temu

I learned about this not long after it came out. That this didn't see a big push my the government during the pandemic and that practically nothing has been spent on ventilation to me are some of the most confidence shaking aspects of how the pandemic was handled

nikolay3 lata temu

I've been researching this and it's too bad that only a few companies produce these, and the pricing is outrageous! I understand they want to make sure only 222nm UVC is produced, but still, come on!

Plough_Jogger3 lata temu

The team at R-Zero Systems has a Far-UV product on the market: https://rzero.com/vive/

[deleted]3 lata temu

beambot3 lata temu

As a safety & security robotics company, we looked at UVC applications early during the pandemic. We came to the same conclusions as Avidbots, which they published online:

https://avidbots.com/resources/what-you-need-to-know-about-u...

TLDR: The level of light insolation you need for disinfection makes them less useful for large area coverage and/or areas exposed to the public due to eye safety concerns.

ajmurmann3 lata temu

Note that this is about far UVC light. There were recent studies that showed that it's safe for humans and multi-celled organisms. The absorption by cells is so effective that the radiation is entirely absorpted by the top cell layer.

lstodd3 lata temu

Disinfection is harmful unless absolutely needed.

Same as overuse of antibiotics - it only breeds more resistant strains and harms the immune systems because of lack of less resistant strains.

msandford3 lata temu

Germs don't get a chance to evolve resistance to this, at least as far as I can tell. At least not any more than humans have the opportunity to evolve a bullet defense.

The UVC doesn't disrupt their metabolism or mutate their genetics subtly, it shreds their chemical bonds.

It's much more like worrying that germs will evolve resistance to hydrogen peroxide or ethanol or iodine disinfectants. It's not impossible of course, but it'll require the kinds of mutations that make them entirely other organisms.

lstodd3 lata temu

> The UVC doesn't disrupt their metabolism or mutate their genetics subtly, it shreds their chemical bonds.

But it does -- this only depends on an prompt dose, at which you have exactly one chance. How can you guarantee a lethal dose (for any definition of lethal) for every single microorganism? Even hard gamma was adapted for, compared to that UV is nothing.

msandford3 lata temu

I guess I don't follow your reasoning. You don't have to kill all of them, you just need to ensure all that get a dose die. If some dodge the death rays, that's ok.

Antibiotic resistance is a thing not because antibiotics are a molecular shredder that chews up the bugs. It's because they're some kind of metabolic poison.

I might be able to increase my resistance to Iocaine powder by slowly dosing up. But I can't increase my resistance to Andre the Giant tearing me limb from limb.

MrOwnPut3 lata temu

> you just need to ensure all that get a dose die.

I believe they were asking specifically that. How do you ensure that?

In other words, how do you ensure all get the correct (lethal) dose?

Some may be partially hit. It would be very hard to tell, no?

msandford3 lata temu

I believe that the way you do this is protocol and dosing.

If you put these in ductwork then you need to look at the flow rate through the duct and the required light flux and then ensure that the supplied flux is well in excess of that.

Remember we're not talking about your normal LD50 toxicity. It doesn't kill by metabolic disruption. It kills by turning the thing from organism into not organism.

If an organism survives it does so not by adapting its metabolism to the poison. It does so by enough of itself not being destroyed that it is able to rebuild.

blacksmith_tb3 lata temu

Potentially - though it's a lot harder to evolve resistance to physical destruction than it is to a given antibiotic. The other aspect, aka 'the hygiene hypothesis' still holds, killing more pathogens may well lead to weakened immune response from lack of exposure.

deegles3 lata temu

The immune system is not a muscle that needs to be "exercised."

wkat42423 lata temu

But it can be trained to recognize diseases at low dosages so it becomes more responsive when you have direct contact with a carrier

lstodd3 lata temu

By that logic vaccines can't work

deegles3 lata temu

Read this: https://www.mcgill.ca/oss/article/critical-thinking-health-g...

[deleted]3 lata temu

aaron6953 lata temu