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I'm not sure I understand how you can draw a comparison between LN2 and small magnets.

An adult could quite easily harm themselves or others when playing with LN2, in a lot of ways that aren't inherently intuitive, or just because they are a bit lax with precautions.

An adult is very unlikely to just swallow a magnet for no reason, much less multiple.

> The CPSC appeared to have been fine with that too; its problem wasn't with you owning little magnets

This isn't true. https://www.cpsc.gov/Regulations-Laws--Standards/Rulemaking/...

"objects that are marketed or commonly used as a manipulative or construction item for entertainment, such as puzzle working, sculpture building, mental stimulation, or stress relief."

Even if they were not marketed as such in any way, any magnet set that was commonly used for this would have to have flux index of 50 kG2 mm2 or less.

The CPSC's ruling basically banned the sale of spherical strong magnets to consumers.

I'm not expert in the field, but what purpose does the average person have for small spherical strong magnets?

I know a few people of various professions, trades, students, and I've never known anyone to have a use for spherical strong magnets that wasn't manipulative or construction item for entertainment.

larger than zen magnets, they're useful in repairing dings and dents in brass instruments

I suspect you’re not using spherical magnets for this purpose?

Is there a list of shapes you consider worthy of retail sale?

You seem to have posited that no use case could exist, and as each person mentions a use, you respond to ask ~"but really?"

I use magnets that are stronger in gaming figures. I have a board game that came with a bunch of "Armor Kits" for the plastic figures. If I just used plastic cement to assemble them, they would no longer be customizable. Instead I drill out small holes for magnets on the various pieces, superglue them in there, and then I can swap our pieces as needed.

I suppose the end goal is still entertainment, but they are a utility piece in this example, and you could use them similarly for anything you are building where you want a small magnet.

I suspect you’re not using spherical magnets for this purpose?

Mostly, no. But they work well if you want to emulate an articulating joint

I'm sorry, but I don't understand what you're saying. CPSC's Final Rule specifically says the action pertains only to magnets marketed as entertainment devices.

Marketed or commonly used

That specifically is an or statement, not and.

They're commonly used that way because of how they're marketed. The idea is that it's probably fine if you're acquiring these in lots on Alibaba the way you would a bundle of sapphire crystal rods or whatever, but it is not OK to sell them on a site that has a streamlined checkout flow and exists to promote the magnets as entertainment.

In other words: it'd be OK if they were sold if you specifically had to know what you were looking for to get them, just like with LN.

(Obviously this is all a moot point now.)

Can you please elaborate why gloves are bad ?

I've never handled liquid nitrogen, but everytime I've seen someone handle it they wore gloves like these:

https://www.2spi.com/category/cryo-gloves/

Perhaps because of the Leidenfrost effect? LN would evaporate before, or very briefly during, contact with skin, creating a cushion of air under the droplet, making it just roll away and avoid freezing of the skin.

Maythe the LN would "stick" to the gloves, freeze them, and then freeze the skin?

Proper long cryo gloves are fine. It's what you are supposed to use. The issue you are mitigating with the gloves is mostly that you may inadvertently touch surfaces which are extremely cold, freezing your skin itself or freezing it to the surface. Due to the Leidenfrost effect one is rather safe from touching LN directly unless it is for more than a couple of seconds.

Gloves are not inherently bad, but the risks they do not protect from are not obvious. For the sake of this comment room temperature is 0 heat, cold is negative heat (offset scale).

Gloves are not a perfect insulator, therefore they absorb heat and cold. It takes time for the cold to permeate the gloves - i.e. you observe significant temperature gradient over thickness of the glove. By the time your hand feels the cold, the whole width of the glove is bloody cold. In order to remove the cold from the glove you need to heat it. The only heat source is your hand inside of the glove, therefore the heat is taken from your hand. You need as much heat from your hand as much cold you have taken from LN to bring the gloves to 0. Unless you remove the gloves when the cold starts to permeate - hello frostbite.

While Leidenfrost effect allows one to splash LN on their hands without any or at least significant damage, gloves simply allow more splashes, not full immersion. Handling LN with gloves is a delaying technique, gloves do not magically protect from cold.

Thank you - this makes perfect sense !

I don't doubt that you are right. But that whole description could, to my inexperienced ears, just as well be an argument as to why you really really should be wearing gloves at all times.

If the gloves slow down the process enough so that when you feel cold you have time to put down the container and remove the gloves (less than five seconds?). I mean, to me I'd imagine that is the sole purpose to wear them in the first place?

It would, I imagine, also help from panic. If you notice that you got LN on your gloves there is less panic than getting it on your skin - less chance of a reflex reaction that just makes things worse.

You are correct, one of the main purposes for wearing gloves when handling really cold/hot materials is to provide that time cushion to handle the thing or contain accident safely. The question was why gloves are not necessarily a good preventative measure.

For example if you are arc welding and some nasty blob of molten metal drops on your hand, gloves will provide "heat through" time cushion to remove the gloves more or less safely (easily removable layer also helps avoid hot/cold blob sticking to your body), but keeping the gloves on will most likely still result in a burn. There is a hidden danger with cold that cold does not radiate like heat and we have much less intuitive understanding of how cold affects the skin. Sometimes people get frostbitten during winter activities without them noticing that something was too cold for too long.

What if your hands have sweated, and your skin freezes to the glove material? Removing the gloves might be difficult to do quickly.

This depends on how insulated they are. You could make gloves that allowed you to stick your hand in -200C all day long. It's the same reason winter coats work, slow heat loss below the body's heat protection and you get unlimited duration.

The problem is most gloves are designed for vastly warmer temperatures and you don't notice frostbite if your hand cools down slowly.

> You could make gloves that allow you to put your hands in -200C all day long

I don't think so. The only way you could make an object like a glove for continuous LN2 exposure, and not have it be 2 feet thick, is multilayer vacuum insulation (like LN2 dewars use). But that would not let you move your hands or fingers at all.

Check out polyimide aerogels, it's flexible and has ridiculous insulating properties. On top of that your hands are providing heat which makes a big difference.

Though I suspect mittens are probably far easier to manufacture as that's what current designs for -60c use. Either way you are not going to have much flexibility, but could grab something.

It's sort of similar with very hot things. I'm a blacksmith, and I rarely wear gloves. Steel is a poor conductor of heat, so if you grab it just a few inches away from the red-hot end you're fine. If you hold it too close, you realize it instantly and let go before any serious damage happens. But if you wear cotton gloves for a while, you'll grab the steel closer to the heat without realizing how hot it is, and then the accumulated sweat inside the glove suddenly vaporizes, and you get a nasty steam burn before you can get the glove off.

Similar thing working in a kitchen: always grab things out of the oven with a dry towel. Use a wet towel once and you'll never make that mistake again: the steam exploding against your skin will hurt you a lot more than the metal on your bare skin would have.

Similar with calfskin welding gloves. They'll protect you, but if you grab something really hot, after a moment you end up with a really hot piece of calfskin against your skin. And when you let go of the hot metal object, you still have the hot calfskin against your skin.

In addition to my sibling comment, the practical risk is that instead of splashes skittering across your skin (probably harmlessly), gloves present an opportunity for LN to get trapped up against your skin, where it will most certainly burn you.

> [the CPSC's] problem wasn't with you owning little magnets, but with companies selling them as novelty stress relieving desk devices to rekindle your sense of childlike wonder and also make excellent refrigerator art (all things on Zen Magnets current page).

One could sum up your use of liquid nitrogen similarly. What something is ultimately used for (play, in both cases), is orthogonal with how hard it is to get. In fact, relying on something being a bit of a hassle to get is probably the wrong idea, as that setup is easily invalidated by someone going through the hassle and then eg giving away the proceeds as party favors.

What we really need is a clear label that points out warning, you're now straying from the herd immunity and now dealing with a novel type of danger. But the problem is we're already drowning in warning labels, as there's no downside on spuriously including them - eg how many times do I have to skim over an admonishment to not use an electrical appliance in the rain? Heck, I've seen a bunch of products lately that don't even come with an instructive manual, just pages and pages of common sense and cya-to-be-ignored warnings. So this hypothetical label would have to be distinctive to stand above the useless chaff and also restricted to only referencing novel dangers, not reiterating basic sense that one should have learned by elementary school.

Unfortunately, under our entrepreneurial form of government the CPSC won't just come up with such an "opt out of us" label standard on their own, as it would diminish their own scope. So a private company has to spend a fortune working to legally define a narrow exception from an adversarial regulator rather than just both working together to solve the problem.

People have been hurt by liquid nitrogen. How many people were hurt by Zen magnets?

Thousands, according to CPSC.

This analysis, linked from the article, makes a strong prima facie case that the CPSC's analysis is unfair.

https://www.youtube.com/watch?v=uLwR81UyceE

In particular, the basis of their "thousands" claim is an overbroad stat whose magnitude actually declined following the commercial introduction of these entertainment magnets in 2009. So the CPSC is either measuring mostly something other than these toy magnets, or miraculously these toy magnets displaced other more dangerous magnet-play, or both.

I am not sure I got what you're saying but it sounds like you, of course, are adult enough to play with fun but dangerous toys. But other people - they are not up to your level, and can't be trusted with such toys, because surely nobody is adult enough to handle it. Since idiots exist, everybody must be treated like an idiot. With some exceptions of course, like you.

I think they are saying that you, too, should be able to get your hands on liquid nitrogen as long as you know what you’re doing. If you have to jump through a few hoops, well, that’s part of the process that demonstrates that you’re competent.

They're not really even hoops. We bought the dewar on Amazon, and we get it filled at a welding supply store. You just have to know what you're looking for. But I can't, like, go to Bed Bath & Beyond and get LN.

Was the question about Bed Bath & Beyond ? I think they were prohibited from selling magnets even on their own site, let alone Amazon or welding supplies store. They were sued to close the sale and recall the product, not to stop selling it to Bed Bath & Beyond. Do you really think the situation is in any way similar?

I think the situation is basically identical. Retail availability wasn't really my point.

Wait, so what was your point? You compare LN - seriously more risky, but available to you, and you think it's great - to magnets, much less dangerous, made not available to anyone, and argument it with "LN should not be available in retail", yet you claim your point is not about retail. And you claim LN being dangerous, but available, is the same as magnets being less dangerous, but completely banned. I must admit if there's a point there, beyond "I like this but don't like that, so the law should follow" it's not easily accessible.

"Not available to anyone" is where you're losing me. CPSC didn't ban little magnets; it banned them when sold as part of an entertainment set. So to extend the analogy: I am fine if you have to go on Alibaba and order them directly from the manufacturer.

Wait, so it's not dangerous if the label says "magnets" but is dangerous if nothing changes but the label says "entertaining magnets"? Makes zero sense to me. Then again, people put "do not swallow" warnings on coat hangers now, so maybe that's what we've gotten to.

They are just talking about adding a little bit of friction to the process of buying something that’s useful but potentially dangerous. What is so difficult about that?

Of course there will be tricky borderline cases, and arguably nonsensical outcomes. That’s true of pretty much every law. It doesn’t necessarily mean it’s a bad law.

Of yeah? When I was 9 or so, I had access to dewars of LN and eventually ended up peeing in one to see what happens. It was fine. I've got you on the children, easy access and the Bed Bath & Beyond!

https://www.youtube.com/watch?v=osKzzED3ASA