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Enthalpy

Covid: Disinfect Money

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Hi everyone !

In shops, one remaining Covid contamination path is money. An answer is to allege that money doesn't host the virus, I read that. Or we can try to tackle the problem.

UV light is known to destroy virusses, including Sars-Cov2. UV LED are available for near-ultraviolet Hg wavelengths, compact, reliable, efficient. This could irradiate the money between the cashier's and the customer's hands, in both directions.

The rest is mechanical design, still imprecise. The apparatus must stop the UV from exiting but irradiate both sides of banknotes and coins.

Both users could introduce the money at the top, say between a pair motorised soft rolls, and grasp it at the bottom, after an other pair of rolls. UV between the pairs of rolls would be blocked by the rolls. Nice for banknotes, but the coins would fall at once. It also needs a soft material that survives UV. This shape has the smallest footprint.

Or a platter would tun slowly. The customer has a sector to introduce and extract money, the cashier has an other sector, and the two sectors in between irradiate the money under a cover. Silica and variants make the platter transparent to UV.

Maybe banknotes and coins should have different paths. Possibly the soft rolls for banknotes and the platter for coins.

The apparatus must be easy to open, and opening must halt the UV emission. Fluorescent surroundings would reveal any UV leak.

Marc Schaefer, aka Enthalpy

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You have introduced a very important topic to all of us but arranging such apparatus can't be an easy task for everyone. There are people who are avoiding transaction with cash. They are using scan and pay system. But not everyone is familiar to this contact less transaction of money. I would ask you to suggest some other techniques to disinfect the banknotes. It will help a lot of people out there.

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14 hours ago, Enthalpy said:

UV light is known to destroy virusses, including Sars-Cov2. UV LED are available for near-ultraviolet Hg wavelengths, compact, reliable, efficient. This could irradiate the money between the cashier's and the customer's hands, in both directions.

What duration of exposure is necessary?

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1 hour ago, swansont said:

What duration of exposure is necessary?

Swansont, here's a link to recent study I've seen: https://medicalxpress.com/news/2020-04-sunlight-coronavirus-quickly-scientists.html?fbclid=IwAR2ZQLaVm5X1N--fJQit5xyxBzSTHp8Ow4vsUfQsNjLKi7VF0HNpEf_Ys2A

They combine virus in aerosol with high diffusion; as I recall. Humidity is also involved. UV exposure as well. Conditions try to emulate outdoors rather than what Enthalpy suggests for money. But maybe you guys can get something else from it. With all factors together half-life seems to be cut down to 1.5 min. There are separate data with just radiation, just diffusion, just UV, if I remember correctly.

1 minute ago, joigus said:

Swansont, here's a link to recent study I've seen: https://medicalxpress.com/news/2020-04-sunlight-coronavirus-quickly-scientists.html?fbclid=IwAR2ZQLaVm5X1N--fJQit5xyxBzSTHp8Ow4vsUfQsNjLKi7VF0HNpEf_Ys2A

They combine virus in aerosol with high diffusion; as I recall. Humidity is also involved. UV exposure as well. Conditions try to emulate outdoors rather than what Enthalpy suggests for money. But maybe you guys can get something else from it. With all factors together half-life seems to be cut down to 1.5 min. There are separate data with just radiation, just diffusion, just UV, if I remember correctly.

For money disinfection, radiation intensity would be crucial, though, so maybe not so useful this study...

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8 hours ago, joigus said:

Swansont, here's a link to recent study I've seen: https://medicalxpress.com/news/2020-04-sunlight-coronavirus-quickly-scientists.html?fbclid=IwAR2ZQLaVm5X1N--fJQit5xyxBzSTHp8Ow4vsUfQsNjLKi7VF0HNpEf_Ys2A

They combine virus in aerosol with high diffusion; as I recall. Humidity is also involved. UV exposure as well. Conditions try to emulate outdoors rather than what Enthalpy suggests for money. But maybe you guys can get something else from it. With all factors together half-life seems to be cut down to 1.5 min. There are separate data with just radiation, just diffusion, just UV, if I remember correctly.

For money disinfection, radiation intensity would be crucial, though, so maybe not so useful this study...

1.5 min was for aerosol. 2 min for surfaces. Typically you look at >5 half-lives for significant reduction. That’s an extra 10 minutes. Assuming people tolerate the 80% humidity (they won’t)

Higher intensity, sure. That should help. I’d like to see a study, rather than someone just whipping this up out of thin air.

 

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2 minutes ago, swansont said:

1.5 min was for aerosol. 2 min for surfaces. Typically you look at >5 half-lives for significant reduction. That’s an extra 10 minutes.

That makes sense. Half the viruses is not so good.

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Admitting that the total doses matters, 100* the intensity would reduce the exposure time from 2min to 1s.

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40 minutes ago, Enthalpy said:

Admitting that the total doses matters, 100* the intensity would reduce the exposure time from 2min to 1s.

100* the intensity boosts you from ~1000W/m^2 solar insolation to 100 kW/m^2. I would worry that the cash will catch fire.

That's 10 W /cm^2

A US bill is ~ 100 cm^2, so it's exposed to 1 kJ

Specific heat capacity of paper is 1.4kJ/kgK (I know currency is not paper) which is 1.4 J/gK, and we have about a gram. Paper burns at ~230 ºC, so we need to raise the temp 210K. Add ~300J and it goes poof.

In one second we add 1,000 J

Also, we're exposing for 5 seconds (five half-lives), so it's 5x bigger than that.

 

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On 5/6/2020 at 10:45 PM, Enthalpy said:

UV LED are available for near-ultraviolet

Near UV isn't good at killing viruses.
The big problem is that , even at the right wavelengths, a virus hidden under a fingerprint is immune.

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13 hours ago, swansont said:

100* the intensity boosts you from ~1000W/m^2 solar insolation to 100 kW/m^2.

UV only.

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1 hour ago, Enthalpy said:

UV only.

The referenced paper didn't say it was UV only, they said it was sunlight. That's where the 2 min comes from. If you have a reference for UV and intensity, by all means, provide it. Like I said, I’d like to see a study, rather than someone just whipping this up out of thin air.

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On 7/14/2020 at 12:04 PM, swansont said:

The referenced paper didn't say it was UV only, they said it was sunlight. That's where the 2 min comes from. If you have a reference for UV and intensity, by all means, provide it. Like I said, I’d like to see a study, rather than someone just whipping this up out of thin air.

Trolling.

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On 7/14/2020 at 11:04 AM, swansont said:

The referenced paper didn't say it was UV only, they said it was sunlight. That's where the 2 min comes from. If you have a reference for UV and intensity, by all means, provide it. Like I said, I’d like to see a study, rather than someone just whipping this up out of thin air.

To be fair, we know that the effect of sunlight is almost entirely the effect of UV.
Virus particles are essentially made of proteins and DNA or RNA.

None of those absorbs visible light so viruses can't be affected by visible light. It won't even warm them up much since it will be scattered or reflected.

So, you can discount the roughly 90% of sunlight that isn't UV*.
Which makes the heating problem roughly 10 times less bad than you think.
It's also likely that most of the "killing" is done by UVB rather than UVA, in which case you can include another factor of 20.
In that case, the thermal load from the UV needed to get a good kill quickly is roughly the same as sunlight.

Which is all very well, but a hair drier is probably easier.
 

*

Based on
Most of the natural UV light people encounter comes from the sun. However, only about 10 percent of sunlight is UV, and only about one-third of this penetrates the atmosphere to reach the ground, according to the National Toxicology Program (NTP). Of the solar UV energy that reaches the equator, 95 percent is UVA and 5 percent is UVB. 

From
https://www.livescience.com/50326-what-is-ultraviolet-light.html#:~:text=However%2C only about 10 percent,and 5 percent is UVB.
 

 

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16 hours ago, Enthalpy said:

Trolling.

!

Moderator Note

Are you accusing or admitting? Can you please do everyone a favor and report a post with an explanation if you think it's breaking the rules, rather than tossing a cryptic post into the conversation? Thank you.

 

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5 hours ago, John Cuthber said:

To be fair, we know that the effect of sunlight is almost entirely the effect of UV.
Virus particles are essentially made of proteins and DNA or RNA.

None of those absorbs visible light so viruses can't be affected by visible light. It won't even warm them up much since it will be scattered or reflected.

So, you can discount the roughly 90% of sunlight that isn't UV*.
Which makes the heating problem roughly 10 times less bad than you think.
It's also likely that most of the "killing" is done by UVB rather than UVA, in which case you can include another factor of 20.
In that case, the thermal load from the UV needed to get a good kill quickly is roughly the same as sunlight.

Which is all very well, but a hair drier is probably easier.
 

*

Based on
Most of the natural UV light people encounter comes from the sun. However, only about 10 percent of sunlight is UV, and only about one-third of this penetrates the atmosphere to reach the ground, according to the National Toxicology Program (NTP). Of the solar UV energy that reaches the equator, 95 percent is UVA and 5 percent is UVB. 

From
https://www.livescience.com/50326-what-is-ultraviolet-light.html#:~:text=However%2C only about 10 percent,and 5 percent is UVB.
 

 

Thanks for adding some rigor to the discussion 

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