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iPhones are allergic to helium (ifixit.org)
1289 points by kwiens on Oct 30, 2018 | hide | past | favorite | 340 comments

> So what else could it be? Well, at the heart of every electronic device is a clock. Traditionally, these are quartz oscillators, crystals that vibrate at a specific predictable frequency—generally 32 kHz.

Watch crystals run at 32[.768] kHz because you can divide with a binary counter by 2^16 and get 1 pps to drive the Lavet stepper driving the seconds hand.

Watch crystals are also commonly used by MCUs for their RTC (real time, very low power clock), but never used to produce the main clock of a SoC or something like that. Mostly because that'd need an insanely high multiplication through a PLL (higher frequency multiplication ~ higher phase noise). Base clock crystals are typically 20-50 MHz.

Quartz crystals used to be hermetically sealed.

> Quartz crystals used to be hermetically sealed.

Are they sealed against helium though? It can get through a lot of materials that more common gases can't.

Traditional crystals come in what's referred to as a "hermetic metal can", i.e. a metal box soldered closed with leads going through glass seals. I don't know if that's good enough for Helium.

The sealing is mostly because of humidity. I wouldn't expect quartz crytals to be overly sensitive to some gas, since they're basically tuning forks; the crystal physically vibrates in a resonance mode caused by and inducing an electric current across the crystal.

Hermetically sealed by definition is airtight, i.e. "excludes the passage of air, oxygen, or other gases". [1] With that said, the diffusion rate depends on both the properties of both the seal and the gas.

[1] https://en.wikipedia.org/wiki/Hermetic_seal

Sometimes, definitions aren't the most mechanically sound constructs available.

Very few air seals protect against helium, the smallest gas. Most materials, even metals, are like sponges to helium. It'll seep through slowly.

I was about to correct you and say that hydrogen is the smallest, but apparently, hydrogen's atomic radius is actually a bit bigger. Helium's radius is smaller due to the larger charge of the nucleus making for a tighter electron cloud.

I too had the same thought, and then thought maybe hydrogen molecule is being considered. Read up to see that hydrogen atom has bigger radius. TIL.

Hydrogen creates molecules H2.

Yup. Larger atomic radius due to less nuclear charge, and it's only stable in molecular form - H2.

Helium can cause problems with the metals containing fusion reactors - He bubbles can get inside the metal structure and weaken it considerably:

"The sun makes energy by fusing hydrogen atoms, each with one proton, into helium atoms, which contain two protons. Helium is the byproduct of this reaction. Although it does not threaten the environment, it wreaks havoc upon the materials needed to make a fusion reactor.

"Helium is an element that we don't usually think of as being harmful," said Dr. Michael Demkowicz, associate professor in the Department of Materials Science and Engineering. "It is not toxic and not a greenhouse gas, which is one reason why fusion power is so attractive."

However, if you force helium inside of a solid material, it bubbles out, much like carbon dioxide bubbles in carbonated water.

"Literally, you get these helium bubbles inside of the metal that stay there forever because the metal is solid," Demkowicz said. "As you accumulate more and more helium, the bubbles start to link up and destroy the entire material.""


Case in point, helium filled balloons that deflate over a couple days.

That’s just because rubber balloons are extremely porous, especially when stretched. They don’t hold other gases well either.

Helium balloons are commonly made out of Mylar instead of rubber, and can keep inflated for weeks.

The type intended for keeping around / in a shop for longer time are, but the children's party type often are inflated on the spot.

Completely irrelevant, yet amusing: At a former employer, we had access to what can only be described as unlimited supplies of hydrogen.

This led - in addition to lots and lots of eardrum-splitting workshop pranks - the occasional kids' party balloons being inflated with hydrogen. (As it was free, which He definitely isn't. HS&E be damned.)

A then colleague of mine claimed they'd cracked a window and caused instant panic at his son's birthday party when a bright spark decided to put a balloon to a lit candle to show the other kids it'd pop.

I doubt the cracked window (given a standard party balloon is pretty small - and a cracked window would likely mean lots of -ahem- eardrum deficiency in the assembled crowd) - but I can imagine it got the kids' attention all right when the balloon more or less exploded.

(We did crack a couple of windows in the workshop, though - you'd be amazed at the bang a litter bag filled with a hyd/ox mixture can produce if set alight.)

Hydrogen alone just makes a soft pop; as you say, for a bang it needs to be mixed with oxygen prior to ignition.

>you'd be amazed at the bang a litter bag filled with a hyd/ox mixture can produce if set alight.

Try a large garbage bag with oxyacetylene mix (do not try this at home).

I guess - never having tried the party balloon trick myself - that such a small amount of hydrogen will mix well enough with the surrounding air as the balloon pops to create a (modest, at least) bang as the mix ignites, but this is just conjecture.

Maybe I'll have to do some empi research one of these days - we do have a few bottles of oxygen and acetylene in the workshop at my current employer.

Hey ho, time for an engineer to pay our welders a visit.

Safety first!

Air filled balloons also deflate over a couple days.

Compare with aluminium coated foil. They don't deflate that fast.

Or intestines of cattle.


Early Zeppelins used rubberised cotton for the gasbags, but most later craft used goldbeater's skin, made from the intestines of cattle

I thought hydrogen was the smallest gas, not helium.

Hydrogen normally comes as a molecule (H2), not an atom.

Correct, but also just as importantly the He atom has both a higher nuclear charge and a full valence shell, which pulls the electrons in more tightly. I’d have to look it up but I believe a single He is even smaller than atomic hydrogen or at least comparable.

Edit: looked it up and yes, helium is smaller than atomic hydrogen.

Depends on your definition of smaller, but apparently it's not clear-cut: https://www.quora.com/Which-element-is-bigger-an-atom-of-hyd...

Well, air is also compound of rare gases of which Helium is one.

I agree it is unlikely to be the RTC clock at issue unless it runs a watchdog of done form. But given that they are using MEMS for the 32kHz clock it seems likely they are using it for other clocks too.

> I agree it is unlikely to be the RTC clock at issue unless it runs a watchdog of done form.

Fairly standard technique to run the watchdog off the RTC clock, because that might still work if the main clock is wonky.

Indeed, and historically, a slower RTC clock was also preferred because it would draw a lot less current during sleep mode. And it allows the rest of the system to throttle the main system clock up and down for power savings.

I said "historically" because I don't know is if these are still important issues on a modern system relative to all of the other things that are probably using the main system clock during sleep mode, and the more generous battery.

Clock throttling is still a thing. Many ARM Cortex-Mx parts, when in deep sleep, draw less current than the self-discharge rate of a standard alkaline battery sitting on a store shelf waiting to be purchased. It is common to leave the RTC running, stash important data in the small RAM that is backed up by a super-cap, and go into a “wait for interrupt” deep sleep mode.

In the embedded world this is very standard; timed wake-up from sleep is driven by the 32.768KHz clock, the code then wakes up faster clocks/peripherals as required by the application.

Nit-pick - you mean to divide 32.768kHz by 2^15, not 2^16 to get 1 pps.

More nit-picking... according to wikipedia Lavet requires two states for one step, so 2^16 looks good based on this.

Damn... I mean 2^14 looks good. :)

If you divide by 2^15, you have 1pps, but two states per second (high/low). That might be enough.

Well, division was to be made with a binary counter. They typically work with rising edge clock, and you get a smaller circuit if you have 14 bits compared to 15 bits. I agree that 2^15 can be made to work by using both edges of clock signal.

Here is the Post-mortem from the OP on Reddit:


There are some fascinating weird stories in that thread.

It reminds me of the classic "500 mile email" https://www.ibiblio.org/harris/500milemail.html

The excel email attachments one was insane, and great writeup


One of my favorite conference talks is semi related to problems like this. https://www.youtube.com/watch?v=fE2KDzZaxvE Brian Cantrill - Zebras all the way down

Thanks. The article has lots of external links but not to the original reddit post...

Helium is very good at getting through the tiniest cracks due to its small atomic diameter. One uses it to find leaks in devices with ultra-high vacuum seals (e.g. in low-temperature physics) by attaching a pump with a simple mass spectrometer sensitive to Helium to the device under test and then using a small helium gun to test different parts of the device from the outside. When spraying it at the leak some of it is pushed inside by the pressure difference and can be detected by the pump spectrometer.

Hydrogen would be even better of course but it is rather dangerous when mixed with air.

Hydrogen would not be better. A helium atom is considerably smaller than a hydrogen molecule. Even if you could use atomic hydrogen, the helium atom's radius is significantly smaller due to the higher central charge that is only partially screened by the "other" electron.

Hydrogen binds with other hydrogen atoms to create H2 which is the only form of elemental hydrogen you’ll see outside of a lab helium is unique in that its singular atom is its own elemental molecule.

It's not unique in that. There are other single-atom molecules.

I don’t know anything about chemistry beyond high school (US public school) but presumably helium is the smallest single-atom molecule you’ll encounter if hydrogen is off the table.

TIL, which others? I thought other noble cases are dimers like Xenon also unlike helium I think all of them now found to form some compounds especially with the fluoride family.

All noble gases exist as monoatomic elements.

They don't form compounds easily but there exist molecules containing at least xenon, radon. Even helium can be made to participate in reactions if pressure is high enough.

You only tend to get a noble gas reacting with something if you approach the arena of irresistible force (fluorine) meets unmovable object (xenon), and get Xenon Tetrafluoride. https://en.wikipedia.org/wiki/Xenon_tetrafluoride

The noble gases have complete electron shells and are quite satisfied with themselves, not needing any bonds with anything else. However, the larger the atom, the more flexibility it has with how many electrons it can hide down the back of the sofa. Xenon is the largest non-radioactive noble gas, so it was the first to have a noble gas compound discovered. Fluorine is just desperate to acquire an electron to complete its electron shell, and will do it by whatever dirty tricks it can manage, which is why it is able to wrest one from Xenon's tight grasp.


This sort of thing (along with Derek Lowe's blog) makes chemistry interesting for me.

Derek's blog is absolutely incredible. For the uninitiated, I suggest to start with the "Things I Won't Work With" category:



It's not unique. It's just the smallest.

That point has already been well-established in all the other comments.

Im guessing it's the only one that's gaseous at room temperature and pressure?

Edit: Never mind, all the nobel gasses.

nit-pick ... Noble Gas, not "Nobel Gas"

It’s not all the Nobel gases, elemental Xenon is Xe2, so are the rest I think they are also not that Nobel anymore everyone of them besides helium was found to form compounds.

Edit: apparently even helium can form compounds it’s just freaking hard to force it to play nice with others - https://en.m.wikipedia.org/wiki/Noble_gas_compound

At the risk of sounding fussy, and hopefully just to inform, these are called "noble gases", and it isn't capitalized (except of course at the beginning of a sentence). No connection with the Nobel Prize or anything else with that name.


Xenon is usually found in atomic form. Xenon dimers are not generally found naturally.

Noble, like nobility, not Nobel, like the Swedish chemist.

Right. "Noble" is also used for the noble metals -- gold, platinum, etc., which are relatively non-reactive.

Huh. I would not have guessed Xenon formed dimers at all, but I'm still skeptical that's its usual elemental form...

Hydrogen would be better. Size isn't the most important factor. Gasses with low molecular mass have higher particle velocities. The velocity affects mixing, passage through holes (including filters), and the speed of sound. Hydrogen is about 2 AMU, 1 for each atom, while helium is about 4 AMU.

You can find the formulas in a typical college chemistry textbook.

If "hydrogen would be better", I guarantee companies that make highly-sensitive cryostats (like companies that manufacture MRIs) would do it.

They don't - even knowing He is more expensive that H, because helium is better at leak testing than hydrogen is

It gets worse than that when your cryo equipment has a “cold” helium leak. Ie, something leaking on the dilution fridge only at helium temperatures (4.2K) and lower, but no trace of a leak at room temp.

Repeated bouts of guessing where the leak might be and trying to plug it (usually by welding or re-machining some part), cooling down, checking if it worked, warming up, ripping some more of your hair out, repeat.

Yeah I had that as well, in that case it was best to replace all the Indium seals right away as like you said it takes 24 hours to do a full cooldown/warmup cycle anyway, so spending a day to make new seals is often faster. That's a part of low-temperature physics I definitely don't miss!

I worked on a system where I needed to reach and maintain pressures of 10^-3 tort, and that was hard enough. I can’t imagine having to deal with helium sensitivity.

10^-3 tort is very low. That will cause lawyers to explode.

Just having fun with your typo...

It's why companies that do stuff with ultra-low-temperature pressure vessels typically dramatically overengineer the devices.

Electronic parts also get helium exposure on the launch pad in a rocket. I know for example there can be helium sensitivity issues on gyros for CubeSats.

Wouldn’t hydrogen only work if it was atomic hydrogen? I thought molecular hydrogen gas was larger than helium.

Hydrogen is soluble in most metals. It will just diffuse right into it, like air flowing through a foam filter.

Added bonus: if the metals in question form chemical bonds with hydrogen, (titanium in particular) it will happily do so, even if it's deep inside the metal. The metal will turn very brittle very quickly if it's exposed to molecular hydrogen.


Even a single hydrogen atom is bigger than a single Helium atom. The charge of the helium nucleus is higher and thus "pulls" the two electrons further inward than Hydrogen's single proton pulls its single electron.

Hydrogen exists as H2 in its elemental form you’ll you’ll need to ionize it to separate it and keep it in an ionized or other way isolated form to prevent it from binding to other hydrogen atoms.

If you are talking about ionized hydrogen, you are no longer talking about a gas. If it’s ionized, it is a plasma.

And if it's a plasma...it's gonna melt whatever you're trying to leak-check :)

As a bonus hydrogen is higly explosive, helium is not.

Hydrogen is no more explosive than other flammable gasses when mixed with ambient air. To get the explosive effect, you need to mix it with oxygen in the right proportion (2:1, molecule-wise) and not have any filler gas such as nitrogen.

One of the dangerous things about hydrogen is its wide flammability range: from 4% to 75% concentration of hydrogen in air. Hydrogen will detonate in concentrations between 18% and 59%. In comparison, gasoline has a surprisingly small flammability range of 1.4% to 7.6%.

What drives this wide range of flammable concentrations? Is it just an issue of low activation energy?

Also the upper end is impacted by the low number of oxygen atoms each hydrogen molecule can react with, in this case it's just one, compared to gasoline with say 8 carbon and 18 hydrogen atoms which bounds to 25 oxygen atoms. Mind you, the size of a gas molecule doesn't affect how many you get per volume at a certain pressure and temperature. So 50% gasoline vapors and 50% hydrogen are both molecule counts, with the former requiring 25 times as much oxygen for full combustion, compared to the latter.

Maybe I'm just a fanboy, but I found one of the most impressive parts of the story, aside from actually tracking down the root cause, was that the iPhone User's Guide actually specifically addresses this, along with explaining that it's necessary to give it about a week for the helium to diffuse.

You just know there was a days-long meeting about "the Helium problem", including graphs of how likely different user-personas are to enter a zeppelin, work in a balloon factory, or attend exceedingly well-funded birthday parties.

After debating late nights about whether to pony up for the new better-sealed clock, someone said "Screw it, throw it in the user agreement."

"better sealed clock" would be the universally used quartz resonator, but that would have added 0.002$ to their cost. Unthinkable.

Nice try! The SiT512 Apple uses is more expensive than a quartz resonator. I don’t have Apple’s specific BOM details, but I’d guess it’s likely something like 2x the cost.

it's only more expensive in small quantities. after you ramp up, it's infinitely cheaper as you can produce them on waffers. also you are thinking BOM alone. the selling point of silicon mechanical instead of crystal is that it can be assembled faster and cheaper, greatly offsetting the item cost.

but don't trust me, see the "advantages" of manufacturers promotion https://www.electronicdesign.com/analog/look-inside-programm...

I think the reason they used the helium-affected clock is because it was smaller, not bec it was cheaper.

What are some of the most egregious cost-cutting measures have Apple take in the past? I’m genuinely curious.

china production?

I think that sticking iPhones in helium balloons is now going to the top prank of 2019.

They probably got that info when they bought their oscillators. From there it should be pretty straight forward to include it in testing procedures.

I feel like the buried lede is that the MRI operators vented large quantities of helium into the hospital's HVAC and didn't think to tell anyone.

Oxygen monitors are standard practice when you have MRI machines and Helium cooling. I would like to assume that this monitoring was in place and it never raised any flags? https://www.pureairemonitoring.com/helium-mri-rooms-around-w...

The air’s usual O2 concentration is ~20.5% and it looks like safety monitors trigger at 19.5% and 18%: https://www.pureairemonitoring.com/all-categories-gas-monito...

Helium makes up less than 0.0005% of air naturally. I’m guessing that increasing He concentration 1000 times to 0.5%, for example, is enough to cause problems for iPhones, but not enough to trigger the alarm or pose any danger to people.

Breathing helium is completely safe as long as the oxygen concentration is near normal. Hospitals have occasionally even put patients with respiratory disorders on helium/oxygen breathing mixtures because the work of breathing is slightly lower than air.

Agreed! The only risk is that if you did release a massive amount of helium in an enclosed space, it could displace enough oxygen to drop the O2 concentration to dangerous levels.

That's why it seems like oxygen concentration monitors are a good idea for hospitals with liquid He. They don't really need to monitor helium levels since that's not the direct cause of problems. It's only an issue (but a big issue) if there's so much He released that it displaces enough air to meaningfully dilute O2 concentrations.

Helium is much lighter than Nitrogen and Oxygen and may not displace them rather it will float at the top of the room or escape to the atmosphere quite easily. Though if it were Carbon Di'oxide it would have been a different story.

This is completely wrong. You're neglecting gas mixing and the entropy gain of solution.

Our atmosphere does not contain mostly O2 and N2 in the middle, with a layer of CO2, Ar, etcetera near the surface. The sugar in a bottle of coke does not spontaneously sink to the bottom.

Sugar in coke doesn't sink to the bottom, indeed, but if you put a sugar cube in water, it first sinks to the bottom, and then (slowly) dissolves.

Likewise, if you release helium in air, it goes up first, and then (quickly) dissolves in the air.

Disperses would be a better word than dissolves.

Diffuse would be a better word than disperses.

Ahh true i didnt consider that. But the gas mixing would happen only at contact level, something like the meniscus between two fluids. i doubt they would homogenously mix unless the molecules have an affinity for each other, in heliums case it is an ideal gas.

Is it even possible to monitor fir helium levels? It’s an inert gas, so I’m not sure if it’s easily detectable directly.

Yes we use helium sensors for analyzing diving gas mixtures. They infer helium concentration based on the thermal conductivity of the gas; there's no chemical reaction.

Yes, with iPhones!

It used to be the most common treatment for asthma patients in fact.

Wasn't a helium mixture also not used for deep sea diving and (afterwards) decompression chambers?

Yup, technical divers that do extremely deep dives generally use heliox or trimix which can contain 70-90% and 30-45% helium respectively at the surface. The ratios change at depth due to how the various gasses compress, but it's still a much higher concentration of helium than what you'd experience in pretty much any other environment. Unlike carbon dioxide, helium doesn't cause respiratory distress which is why it's a good replacement for nitrogen during deep dives, and also why it's so popular for suicides

Considering that Trimix and Heliox used in deep commercial dives can have the majority (Aka >50%) of the breathable “air” be helium, your theory that there’s really any risk of danger to people seems a bit unwarranted to me.

Helium isn't toxic but it displaces oxygen. Heliox still contains enough oxygen to breathe (at sea level it's 21% oxygen just like normal atmosphere, and when diving the partial pressure of oxygen is the same as oxygen in normal atmosphere). But if you release helium into a room full of air, patients with already-compromised respiratory systems from injury or from respiratory diseases or from opioid painkillers could be at risk for brain damage or death if they were borderline already and not being monitored closely enough.

The author's cavalier "I bet the nurse’s voices were higher pitched that day!" was incredibly inappropriate given the potential danger.

> Helium isn't toxic but it displaces oxygen.

While technically correct in theory, in any real world environment Helium will not displace Oxygen unless you are dumping orders of magnitude more helium than in this scenario.

> Heliox still contains enough oxygen to breathe (at sea level it's 21% oxygen just like normal atmosphere, and when diving the partial pressure of oxygen is the same as oxygen in normal atmosphere).

There’s so much wrong with this (and the rest of your post) I can’t think of a polite way to respond, so I’ll just wish you a good day.

I’ll admit I haven’t gotten that far in my diving certs yet, but isn’t the point of Heliox so that you can have less than 21% O2 at high depths to avoid narcosis and a fatal ppO2?

To simplify it a bit.

The point is to keep partial pressure of oxygen below that of maximum safe limit of 1.2 to 1.6. For example, 100% oxygen at surface is 1.0 and thus safe but will very fast reach maximum when you increase the pressure just by a few meters. Regular air with 21% oxygen will start to be a problem at 50 meters, so divers that need to go deeper need to use mixes that has less than 21% oxygen. When a mix is less than 18% oxygen they become hypoxic and cannot safely be used at shallow depth.

So the point is not to get "the same as oxygen in normal atmosphere". It is to keep the partial pressure of oxygen within safe limits, usually between 0.18 pp02 and 1.4 pp02 depending on a multitude of factors and safety margins.

The only point I was trying to convey with that statement was that there might be much less oxygen by volume in deep-diving heliox but the partial pressure of oxygen is still maintained so that cellular respiration can continue normally. Was that the only thing you thought was outrageously wrong with my comment?

I am not jsjohnst, but the only additional nitpick is that Heliox is any blend that is exclusively helium and oxygen and the reason why heliox is more commonly used for deep dive is that helium has less resistance compared to nitrogen, meaning that pushing compressed air through ones respiratory system takes a bit less effort. Helium in heliox is thus used to displace the nitrogen, with the oxygen ratio being adjusted based on health, depth, bottom depth, purpose, decompression, surface interval and so on.

Kind of, a fatal ppO2. But in a hospital room you have the other kind of fatal ppO2, the kind where you pass out and need an O2 mask.

Hospital rooms aren't hermetically sealed. Helium dissipates so quickly that this isn't a realistic safety concern.

Helium rises. Not slowly. It really rises very quickly. Patients are in beds, horizontal, many also on oxygen feeds. The nurses are standing. Their voices would indead become higher in pitch long before patients were impacted.

If thier voices were rising, id suspect helium but would be worried that some reaction released hydrogen. Same squeeky voices but a serious fire hazard.

I remember these constant problems with helium tanks in rockets. It's way harder to keep helium in place.

You need ~0.2 Bar of oxygen partial pressure. The purpose of Trimix/Heliox is to keep oxygen partial pressure under 1 Bar while also reducing nitrogen to prevent narcosis. You can't breathe the 200m mix at sea level pressure.

> You can't breathe the 200m mix at sea level pressure.

What makes you think you can’t (other than it being hypoxic)? You most certainly can breath Heliox, in fact, it has been used medically[0] for almost 100 years, far longer than used for commercial diving.

[0] https://en.m.wikipedia.org/wiki/Heliox

Heliox doesn’t denote a specific concentration of helium and oxygen; even just within diving the mix varies depending on the depth it is to be used at.

Correct! A common ratio for deep diving is 12/88, but 21/79, 30/70 and 40/60 are also used at less depth.

In fact, Heliox would usually not be used for dives to 200m due to HPNS risk. Usually it would be Trimix for that.

Either way, GP is mostly wrong on the points they made.

Also, the oxygen partial pressure you need to stay under is 1.6 Bar for oxygen toxicity. Huge difference between 1.0 and 1.6, depending on oxygen percentage, the difference could be a >50% reduction in MOD.

Thank you for spelling "breathe" correctly. It seems these days I see it spelled wrong more than I see it spelled correctly.

The only risk is that the O2 levels drop too low from a massive release of He...and while I'll 100% agree this is a very minor risk, I'd still rather hospitals play it safe and install O2 deficiency monitors.

The article I linked mentioned that O2 monitors are legally required for hospitals in NYC. That regulation might have been created because in 2000 someone working on an MRI machine died from a Nitrogen leak (it's also used for cooling and like He, the only risk is that it displaces O2). It's likely this person wouldn't have died if an O2 monitor was in place that sounded an alarm fast enough for the victims to leave the area. http://www.nydailynews.com/archives/news/nitrogen-gas-leak-k...

edit: googling a bit more found some interesting references on dealing with "oxygen-displacing gases". O2 monitors are on the long list recommendations/requirements. One thing I found interesting is that at one laboratory part initial assessment involves a controlled release of the maximum amount of gas that will be stored and then measuring the drop in O2.



It is the main reason you have to be careful with working with liquid nitrogen in closed rooms: the danger of displacing too much oxygen. While our breathing air consists of 80% nitrogen, when you evaporate large amounts of liquid nitrogen (like 10 liters in an instant) in a closed room, there is the danger of displacing oxygen to a dangerous level. Working with smaller amounts (like 1 liter) is quite safe though.

Not enough to directly endanger people, but a hospital is full of electronics that plenty of people need to live, and it sounds like they could potentially share the iPhone’s vulnerability.

If it makes you feel better:

Hospitals of reasonable size typically have an on-site clinical engineering team that handles those kinds of situations. Important (that is, capital expense category) hospital equipment will typically emit all kinds of warnings and alarms way before anything's actually a problem, because everyone would rather rely on the on-site engineering spending a little extra time silencing false positives then leave anything to chance.

All the nursing journals are full of articles about combating “alarm fatigue”. After 1 google query and 2 minutes of link-clicking:

> “An analysis of alarms at The John Hopkins Hospital, Baltimore, Maryland, revealed a total of more than 59 000 alarm conditions over a 12-day period-or 350 alarms per patient per day.1,2”


Alarms are mostly ignored or turned off.

If you spend any time in an emergency room or a hospital, you'll soon realize that there's almost always an alarm going off somewhere, usually more than one and usually for long periods of time.

> Hospitals of reasonable size typically have an on-site clinical engineering team that handles those kinds of situations.

Not for superconducting magnets they don’t. They may be involved with MR scanners somewhere, but that would be extremely uncommon.

It's not an issue for most equipment though because it's only really the MEMS type oscillator that is sensitive to this type of gas intrusion. It's a very new type of clock and most other devices don't use them so there's basically zero risk.

Unfortunately the O2 sensors were being monitored by an iPad.

Or the O2 alarms just don't work and the hospital was negligent.

Occam's razor.

Indeed. I had to reread that paragraph. That's a LOT of helium (by volume).

"So, i noticed some of the workers' iwatch's weren't registering the users' heart-rates. At first, I thought it was because they had all died from suffocation from the massive gas leak. But, then I discovered something interesting... it was actually the helium molecules worming their way into the internal clock chip! Amazing day."

Yeah, but at the same time, it wasn't enough to set off the alarms for low oxygen content, which is at least a little disturbing, right?

Not necessarily.

Nobody could adequately explain to those of us in the CS dept why we had to take 3 semesters of Chemistry. Bits of it hung on and from other sources such as space exploration articles I recall this much:

Fires and lungs both operate on partial pressure of oxygen. As long as nothing else in the air is toxic, your body cares that it gets X oxygen molecules per cubic centimeter of air in your lungs, not Y parts per million. Those deep sea submariners are breathing mostly helium with a small fraction of oxygen in it. If you just compressed surface air there would be so much oxygen that your hair would explode when you ran your hand through it. Assuming the electronics didn't burst into flames first. And if you didn't set yourself on fire, that much nitrogen would kill you pretty quick.

So the question is, does helium displace air or mix in with it? I believe the answer is 'some of both'. If that's the case (and I think we can infer that from "the alarms didn't go off") then a good amount of helium might reduce the oxygen partial pressure less than going to 3000 feet above sea level. So what's the Venn diagram of COPD sufferers, in a hospital wing near the MRI machine, that aren't currently on supplemental oxygen?

Moreover, helium floats to the top and escapes through any opening (staircases, HVAC ducts, gaps in ceiling tiles) because it is lighter than air. This makes it much less dangerous than a heavier gas such as CO2 even if there's enough of it to displace a significant amount of air.

Not just any opening: just about any microscopic crack would let it out and most non-metal materials are effectively porous when trying to contain helium under pressure. It's even used to detect leaks in high vacuum chambers.

You don’t even need cracks. Helium (and hydrogen) can diffuse through metal, especially at high temperatures. Hydrogen embrittlement is a problem for processes that use high temp hiydrogen like the Haber process.

how is it typically dealt with? regular annealing?

I’m not sure about in modern processes, but Bosch’s original solution for the Haber-Bosch industrial process was to just periodical replace an expendable steel liner in the reaction vessel.

That is not true by any stretch of the imagination. If gases behaved like that then we'd all be choking on a layer of argon with all of the oxygen out of reach above us. No, gases diffuse and mix easily.

Gases diffuse and mix given enough time. There's not enough time when you have a massive indoor gas leak.

Even outdoors, large amounts of CO2 tend to sink to the ground and suffocate people in low-lying areas. Look up Lake Nyos for a particularly grizzly example of that.

Helium breathing mixes are for deep sea divers, not submariners. Most submarines run an interior gas mix nearly identical to regular air.

I didn’t mean navy boys, I meant research submarines at extreme depth.

Research submarines at extreme depths also use regular air. There's really no benefit to helium mixes for submarines. The breathing gas isn't compressed, it's at about 1 bar.

Odd, I assumed that subs would run at least a few atmospheres to compensate for pressure differential. Structural assistance not worth giving the crew the bends on fast ascents?

Why bother with 2-3x more air pressure and all the problems that go with it (crew decompression, lack of abort options, etc.) when the outside pressure is hundreds or thousands of times more? You're really not gaining anything engineering-wise.

One thousand times would make it 10km depth - so clearly not “thousands”. Other than that you are right that there is no gain in e.g. doubling the internal pressure.

Yes I made a mistake in my estimation there. Max pressure at the challenger deep is about 1,000 atmosphere, so that shouldn’t have been plural.

The pressure outside is +1 bar per 10 meters. If you're 1 km deep, that's 100 bars (+1 atmospheric bar) while it's ~1 bar inside the sub. The mechanical stress on the submarine depends on the pressure difference, not the ratio. So increasing air pressure (with all the complications and risks it would bring) would only reduce the material load by a few percentage points.

Then why all the videos of people who sound like garden gnomes?

Which videos?

I assume the first two semesters were first-year (freshman) chemistry. What was the third year? Organic?

As long as there is enough oxygen in the air, what's disturbing about it? People breathe helium/nitrogen/oxygen mixtures all the time.


I didn't mean that the air would be dangerous to breathe.

I meant that it's disturbing that the amount of He needed to disable the iPhone is low enough that the standard sensors around He (which measure 02 levels) don't regard it as a major leak for He to be at that level.

Virtually all (esp. consumer) devices assume 'normal' atmospheric conditions with 'normal' temperature ranges and 'normal' humidity ranges. As you start to go outside those ranges, strange things can happen. People at extreme altitudes and/or in extreme climates see this on some types of devices. It's not a big deal. If you have needs outside the typical ranges, you provide your specifications and be prepared to pay much more for your solution.

Why would that be disturbing? Electronics and organisms do not have identical environmental tolerances/intolerances.

Presumably, the sensors exist to protect humans, not electronics.

A device-disabling threat that normal threat sensors can't detect, even when those sensors have been deployed because of the chance of unusually high levels of that threat?

Yes, I'm allowed to be disturbed by that; why wouldn't you be?

Not at all.

The devices are tested for usual STP. Nothing else, unless specified. They are done so not for human comfort, but for tested conditions. No more.

If you want extreme conditions, pay through the nose.

Helium, unlike carbon dioxide, is lighter than both oxygen and nitrogen, so it would rise in the rooms and be very unlikely to displace oxygen in people and set off any oxygen alarms.

In addition, unlike carbon monoxide, helium doesn't bind to, well, anything and certainly not hemoglobin, so it doesn't present a momentary exposure hazard either.

See other reply -- I wasn't referring to danger to humans.

What the heck? I clarified that I was concerned about the silent danger to the iPhone, not to humans, and people keep assuring me there’s no danger to humans, and giving me flack just for saying that wasn’t my concern? This is a weird thread.

Quoting you:

> Yeah, but at the same time, it wasn't enough to set off the alarms for low oxygen content, which is at least a little disturbing, right?

First, alarms for low oxygen content are set for people and no other reason. There can be alarms for high oxygen content, but they are extremely rare and would likely not be present in very many places in a hospital.

Second, why in the world would low oxygen be a danger to an iPhone?

You can't make a complete non-sequitur of a logic leap and then expect everybody to be on board your train of thought.

I wasn’t comaplining about that, but for getting to -3 for pointing to a reply where I clarified the concern.

Furthermore, comments were rolling in assuring me of the nonthreat to humans after I clarified.

You called it "disturbing", so the clarification that you were not intentionally implying any danger whatsoever is kind of annoying.

“Device disabling threats that aren’t detectable by the usual sensors” can’t count as “disturbing” because a human didn’t die?

"threat" the way UV light is. So no, not disturbing for it to silently ignore the equivalent of popping a party balloon.

Bricking your iPhone for a week-plus is not the equivalent of popping a party balloon or a short dose of UV light!

And yes, I get it, the sensor exists to detect for threats to life, not threats to iphones. But that's the point: this is a threat we're not set up to watch for at all -- hence why it took so much investigation to root-cause it!

Are you still going to make it your hill-to-die-on that it's "not disturbing"?

Come to think of it, did that "lack of faith" scene in Star Wars (1977) also seem confusing to you?

> Bricking your iPhone for a week-plus is not the equivalent of popping a party balloon or a short dose of UV light!

You totally misunderstood my comment.

I mentioned popping a party balloon because it could also disable your phone. And UV light because it can also destroy certain electronics. But sensors that can pick up little bits of UV are normally not set to warn about it, and that's perfectly reasonable and not "disturbing".

We can use a different word if you want. You think it's a [significant] problem and I don't think it's a problem. Is that better?

I'm not here to die on the hill of word choice. I disagree with your underlying opinion.

Sorry -- do you have a citation on that? If popping party balloons could disable iphones, I think we'd hear about it more often. (I can't find anything about it on a quick search, and I hope I can be excused for missing an analogy that depended on an invalid premise!)

What made it unnoticed for so long was that it required the much larger MRI He release to trigger. What (I claim) makes it disturbing is that an expensive incident can happen (bricking a hospital's iphones for weeks) at levels that no one currently calibrates sensors to check for, because no one expects that level to have a negative effect of such magnitude.

Regardless of your preferred terminology, it seems odd to take an attitude of "oh, it only deleted everyone's second-brain for week, in a way that was hard to root-cause, no one died, no big deal" and therefore balk at the use of "disturbing".

I mean, do you consider undetectable, inexpensive phone-bricking techniques to be generally "non-disturbing", or just this one?

> Sorry -- do you have a citation on that? If popping party balloons could disable iphones, I think we'd hear about it more often. (I can't find anything about it on a quick search, and I hope I can be excused for missing an analogy that depended on an invalid premise!)

Some of the tests were just plastic bags with tiny amounts of helium in them. Unless you're asserting some exceptionally strange gas physics here, you can break an iphone with some balloons.

> Regardless of your preferred terminology, it seems odd to take an attitude of "oh, it only deleted everyone's second-brain for week, in a way that was hard to root-cause, no one died, no big deal" and therefore balk at the use of "disturbing".

> I mean, do you consider undetectable, inexpensive phone-bricking techniques to be generally "non-disturbing", or just this one?

Hang on. You were calling the calibration of the air quality sensors disturbing. That's what I objected to. I wasn't making any claims about the iphone bug itself.

And nobody was talking like Donald Duck either so I would guess it was leaking out of the room at a pretty hefty rate.

Depends on where the sensors are located. If at head height, the helium may occupy the layer above and tall people would have a hard time.

Sadly, the plant used Apple's iSensors which don't work in the presence of helium.

What a relief that must have been.

Another scary practice is venting natural gas indoors. Most of the time it's fine, but sometimes you get a catastrophic explosion: https://www.youtube.com/watch?v=rjxBtwl8-Tc (The US Chemical Safety Board has a bunch of interesting videos.)

This is nuts! Why would you even vent flammable gases indoors on a construction site?!

Because when you initially pressurize a newly installed portion of pipe, it's not filled with natural gas, it's filled with air. Air doesn't burn, something like a natural gas burner with a pilot light is going to detect that the pilot light went out and shut off the gas flow to prevent an explosion. That leads to a sort of catch 22, you can't purge the line without the burner going and the burner won't turn on until the line is purged.

Ideally you would pressure test and purge new work with nitrogen as well in order to prevent a potentially combustible mixture from forming inside the pipe while the air is being purged from it.

As to the safety of purging natural gas directly indoors, obviously that carries some risk but it's not as dangerous as you might assume. Below a certain concentration (5% by volume) natural gas mixed with air actually won't burn freely. Also above 15% natural gas by volume won't burn freely. The risk of an explosion is only present in that 10% range. If you're putting in a new gas stove in your kitchen and you crack open the valve with the hose off of the stove until you smell gas, that's not a ton of natural gas that you've let out into a room with a relatively huge volume. The pressure of a natural gas pipe in a house is actually very low, only around 0.25 psi. It's coming out slow enough that you've got plenty of time to turn off the gas before you come anywhere close to hitting that lower explosion limit where things get extremely dangerous.

They thought they were venting outside. It only went inside because of an undetected leak.

As long as he helium doesn’t displace the oxygen it is fine. Saturation diving has people living in “heliox” environments where the atmosphere is helium and oxygen.

There are more details in the original thread https://www.reddit.com/r/sysadmin/comments/9mk2o7/mri_disabl... on reddit:

I discovered that the helium leakage occurred while the new magnet was being ramped. Approximately 120 liters of liquid He were vented over the course of 5 hours. There was a vent in place that was functioning, but there must have been a leak. The MRI room is not on an isolated HVAC loop, so it shares air with most or all of the facility. We do not know how much of the 120 liters ended up going outdoors and how much ended up inside.

Except that Helium is not dangerous whatsoever and to actually displace oxygen you would need much much more than that.

Venting 120l of liquid helium (or about 84,000l of gaseous helium) really isn't that much of a health concern

I've seen multiple vents of ~1500l of liquid helium (~1,050,000l of gaseous) in a single day from a couple bad MRI units when I worked at a company that makes them

Only "dangerous" place to be was in the fragmentation path of the burst disc (which was enclosed in the top of the unit (at the time)), or directly in the path of the nearly-liquid (ie extremely cold) helium as it vented

It dissipates extremely rapidly

Yea, that sounds incredibly dangerous considering how easily you can suffocate inhaling helium

how easy is it? It floats, so it only fills a room from the top down... and if you fall over unconscious, you're automatically moving to a part of the room with more oxygen. it would have to displace all of the air in a room in order to suffocate someone, no?

It's fairly difficult, but definitely possible. It's hard to recognize because what is killing you is the lack of oxygen. People generally don't notice they are becoming hypoxic.

But there are plenty of things to help you out here. First is that helium is very light. So if you pass out and fall down you will be in a lower concentration of helium (assuming you are not in a sealed room). (Labs with heavy gases have vents on the floor) If the room is reasonable ventilated you should be fine. It dissipates fairly quickly. Helium permeates through most things, but this is a slow process so probably won't save you.

I meant more that you don't feel like you are suffocating when you are inhaling helium, so it can be hard to realize something is going wrong until it is too late. Definitely easier to suffocate with heavier-than-air gasses though.

Multi-story building. The floor could be, given enough gas, under.

If helium is small enough to get in a watertight phone, it is certainly small enough to dissipate in a probably not so watertight building.

Quenching MRI magnets can suffocate people in the room they quench, and potentially the entire floor. I don’t know about a whole building, but just because something can dissipate doesn’t mean it can’t do damage in the meantime.

Not true - the whole point of burst discs etc in MRIs is so that if a quench happens, the patients and any technicians in the room survive

Venting even a full MRI's worth of LHe (~1500l) as most will make you a little lightheaded for a few minutes

The risk of death from quench events is effectively non-existent

If you fall over unconscious from helium then you'll probably die without immediate help. Your natural breathing reflex is triggered by the presence of CO2, not the lack of oxygen. If you inhale a lot of helium and pass out, your body doesn't start breathing again because there is no CO2, so you just suffocate instead of inhaling oxygen.

You're continuously producing CO2 whenever you're alive. If you fall down and land in a normal atmosphere then your normal breathing reflex will save you. Low oxygen atmospheres don't stop you from breathing; they're dangerous because you continue breathing as normal. The CO2 is carried away from your lungs with each breath, so there's no feeling of suffocation.

> If you inhale a lot of helium and pass out, your body doesn't start breathing again because there is no CO2, so you just suffocate instead of inhaling oxygen.

Other posters have pointed out that this is false(you will continue producing CO2 while unconscious just fine, chemoreceptors will notice). I would like to add that I have personally witnessed people falling unconscious from helium. They recovered just fine.

Really, the greatest danger is the fall.

you don't breathe because there is CO2 in the air, you breathe because there is CO2 in your blood

If that were true then divers would have to bring canisters of CO2 down with them.

Well helium rises. So falling down is a good thing, as most vents are above you. If you go to a lab with heavy gases you'll notice vents on the floor for exactly this reason.

Right! It's not like an "allergy" to helium is going to be a problem for any user at any time unless, you know, there's a big helium leak, at which point the phone is the least of your problems

Wouldn't this affect people's voices?

Eventually. But I would expect that by the time the effect is noticeable, the concentrations will be too high to support consciousness and will have been for some time.

I'm not sure that's true.

If you displace 30% of the atmosphere with helium, the O2 concentration drops from 21% to 15%. That's low enough that you'll probably start to see mild cognitive impairment, but it's still plenty capable of supporting life. However, a 30/70 mixture of helium and air is about 67% as dense as normal air, which means voices would be pitched more than half an octave higher.

Considering the current helium shortage it's a shame they just wasted it.

This is the first time that I remember seeing a story evolve on the internet. What was originally from a post on r/sysadmin 3 weeks ago is now summarized on a Blog article that's at the top of HN. Will it get picked up my mainstream media and be on everyone's news feed by next week? Or tomorrow, now that its picked up momentum? Besides being a really fascinating story, its having an interesting journey as news travels through different outlets and gets condensed and filtered down to more consumable forms.

You weren't around when the Meltdown rumors started?

I remember hearing plenty of whispering that Intel had a major bug disclosure coming up, but for most of that time I feel like the majority of speculation was centered around the Intel ME.

Sadly my immediate reaction to this post on /r/sysadmin was to discount it, or rather attribute it to some external factor that nobody could possibly figure out and entirely unrelated to the MRI. In this case I was quite happy to be proven wrong by the follow up posts and subsequent article.

I'm really curious why something they can generalize to "helium leaking into the quartz oscillator" only affected Apple products. What feat of manufacturing keeps a broad range of OEMs safe on the Android side but so eludes Apple? Worse yet, was some "cost savings" engineered between iphone 5s and 6 that ultimately introduced this issue?

It wasn't a quartz oscillator - it was the MEMS oscillator that Apple was using in place of a quartz oscillator that is speculated to be the root cause.

The other phones involved still used quartz.

From the article:

"But quartz oscillators have some problems. They don’t keep time as well at high (and low) temperatures, and they’re a relatively large component—1×3 mm or so. In their quest for smaller and smaller hardware, Apple has recently started using MEMS timing oscillators from a specialized company called SiTime to replace quartz components.

Specifically, they’re using the SiT512, 'the world’s smallest, lowest power 32 kHz oscillator.' "

So it was size, not cost that led Apple to be using a susceptible component.

No doubt it will move to mass media

We had this problem too.

Every time my colleague brought his phone to the control room the Cellular stops working for like a day or two, but my 6s worked just fine anywhere even next to a Dewar that's venting Helium. Now the mystery is solved!

BTW, among us there are others who accidentally brought their phones near or even into the MR bore during maintenance, but none of these devices has done any permanent damage to our phones, except one accelerometer on a cheap Chinese phone, even in a 7T magnet. So I never thought that MRI could be causing the problem.

It's in the iPhone user guide ... maybe not something everyone reads, but it has been known for some time

That said - a 120l leak of liquid helium is both stupidly expensive, and highly damaging to the MRI unit: there's a bath of ~1000-1500l of liquid helium in an MRI to keep the superconducting coils at superconducting temperatures. Losing ~10% of that volume probably means the unit won't work

When you install a new unit you use additional helium that boils off just to bring it to superconducting temperature.

>When you install a new unit you use additional helium that boils off just to bring it to superconducting temperature.

Nope - well, not with any of the ones with which I am familiar: they're shipped full most of the time

Few things; Isn't it a bit odd that a hospital MRI machine room isn't being monitored for these kinds of things? I'm curious, not accusatory.

Also, this could be a potentially catastrophic tool for terrorists. As trivial as it sounds, it's even worse than a traditional frequency jammer because it renders the device unusable instead of just not being able to communicate with the outside world.

Edit: On the other hand, interesting counter-terrorism tool as well. Is there any precedent for the CIA using this sort thing intentionally?

There are almost certainly oxygen sensors in that room. The helium concentration was probably not high enough to displace enough oxygen to trigger them. Though it wouldn't entirely surprise me if they were ignored or disabled.

Liquid helium is rather expensive and would likely draw attention in areas where it's not usually handled. Really doesn't sound like a useful terrorism tool.

Honestly, even Sarin nerve gas isn't a very useful terrorism tool.

I think the infamous Thunderf00t does a decent job of explaning why https://www.youtube.com/watch?v=l6uLUaqgWY0

I love him, will watch

Thanks for the info! Did the article mention that it had to be liquid helium then?

I assumed liquid helium because that is what you need to fill MRI/NMR machines. You could use regular helium, but the pressure bottles are also rather conspicuous. And releasing large amounts from both is not a subtle process, so I really doubt that is practical.

To be clear, not arguing, I just want to learn. Doesn't this contradict what you said before though, about it not displacing the oxygen sensors in the room because it was so little? "We do not know how much of the 120 liters ended up going outdoors and how much ended up inside. Helium expands about 750 times when it expands from a liquid to a gas, so that’s a lot of helium (90,000 m3 of gaseous He)." I wonder what this would mean in practice at any given time.

I'm very certain that there are usually oxygen sensors installed for MRI machines and NMR spectrometers. I'm not sure how sensitive they are. Either they were not triggered, e.g. because the helium concentration was low, or at least low at the position of the sensors. Or if it was high, they were disabled or ignored.

120 liters of liquid helium is a lot, but it wasn't released at once but over a longer time as far as I understand the story.

Some have sensors and some don’t. GE ones do in my limited experience (one scanner), other vendors don’t (experiece limited to half a dozen scanners).

I don't mean sensors directly attached to the machine. My experience is with NMR spectrometers, which work based on the same principle as MRI machines and have the same superconducting magnets that require liquid helium and nitrogen. And those essentially always have an oxygen sensor in the room somewhere, but not connected to the spectrometer itself.

Yes - that’s what I mean too. GE located theirs in the scanner control room. The other vendors didn’t have them. I’m going to confirm this as I’m doubting myself now, but the GE one would fail every few years as the sensors have a limited life. It was ear splittingly obvious that they had one.

It was monitored. From the original thread https://www.reddit.com/r/sysadmin/comments/9mk2o7/mri_disabl... on reddit:

One of our multi-practice facilities is having a new MRI installed and apparently something went wrong when testing the new machine.


I discovered that the helium leakage occurred while the new magnet was being ramped. Approximately 120 liters of liquid He were vented over the course of 5 hours. There was a vent in place that was functioning, but there must have been a leak. The MRI room is not on an isolated HVAC loop, so it shares air with most or all of the facility. We do not know how much of the 120 liters ended up going outdoors and how much ended up inside.

The idea that some terrorists are plotting to ruin our phones with helium, and that we should consider it "catastrophic" is laughable.

Scaling a "helium attack" against electronics is one of the dumber terrorist plots I've come across. But let's play.

Say I scored a big truckload of helium, 5000 l. (The contents of my tank will expand to 3750 m3 of He gas.) Then I got access to a ventilation duct into the subway. I manage to hook up my tank and start depleting into the subway. Assuming 20 m2 cross-section for a tunnel: if I could do the emptying at once, I could fill 0.187 km of tunnel completely with He; killing all vermin in that section.

But hey my goal is not to suffocate (that would be boring, right?) but to fritz electronics. So I do it slow and steady into a station. Say I want to keep the concentration of He in the station at around 0.1%. (I assume it would take time for operators to detect this. I don't know how sophisticated gas detection is in subways.) Let's assume an airflow of 5 m3/s into that station. I'd need 0.005 m3/s He or 400 m3 per day to keep the level at 0.1%. So for only one day, I'd need to get around 500 l liquid helium into position.

There are easier pranks to play.

If you are a terrorist, why not get a big truckload of fertilizer? Easier and actually kills people instead of just wrecking their apple devices.

Or if you are some kind of compressed gas terrorist, 5000L of compressed oxygen or acetylene will do a lot more damage than helium.

Anyone who can mount a helium attack can mount much more severe attacks.

I think the probability of some eccentric and well-supplied terrorists trying to ruin Apple devices with helium is so remote as to not be worthy of consideration.

Even if it does come to pass. Oh well, I'll buy another iphone, or an android.

The point of terrorism is to cause terror and to inspire parallel independent actors.

About 3000 people died on 9/11, but we acted like it was the next Pearl Harbor. These 3000 people died needlessly, and it sucks, and my heart goes out to the families who lost someone that day, but statistically was a tiny blip.

9/11, as an act of terrorism, was successful. We now can't get out of the Middle East, it caused a decade long economic depression that snowballed into the housing crash, it ruined our relations with other nations, and hating Muslims is the ordre du jour like it is 1099.

Lol you clearly underestimate some people, but I'm wondering what makes you think that even a frequency jammer in the wrong hands couldn't be potentially catastrophic?

>but I'm wondering what makes you think that even a frequency jammer in the wrong hands couldn't be potentially catastrophic?

It is, but only in the same sense that a van in the wrong hands could be potentially catastrophic.

Define "catastrophic" in the context of Apple devices ceasing to function.

I love HN. I came here to learn more about MEMS RTCs, something I've never heard about previously... But most of the discussion is about the dangers of a helium leak... Which is a good point, especially if that leak is in a hospital.

A bit of googling on MEMS RTC revealed this slightly dated article which I thought was still interesting: https://www.maximintegrated.com/en/app-notes/index.mvp/id/55...

Turns out one of the main reasons to switch is for the smaller packaging vs quartz oscillators.

The picture in the article that is labeled as an MR scanner is a CT scanner, and the people are wearing lead for radiation protection.

The photo is labeled "Morris Hospital’s GE Medical BrightSpeed CT Machine"

It said ‘MR’ rather than ‘CT’ when I commented, and now it’s a completely different photo with a new caption.

It's good that he was able to reproduce it (although with a far higher concentration of helium), but the original story showed up a few weeks ago at an EE forum I lurk, and everyone there was skeptical of helium and suspecting EMP instead:


But an electromagnetic pulse would have taken out medical equipment in the facility as well, and they were working fine!

I suspect medical equipment is designed to a higher standard of EMP resistance than most other products, especially equipment designed to sustain life. Phones also have antennae specifically designed to pick up EM fields, while medical equipment like an EEG or ECG is specifically designed to reject them.

Likewise, the devices "reviving" after a week is not unusual if they're just resetting due to power loss. Immediately disconnecting and reconnecting the battery would for sure differentiate between helium (device remains dead even after reset) and EMP (device reboots successfully.)

But Android phones were also unaffected.

Any particular reason you're ignoring the fact this only happened to iOS devices? Do the various Android manufacturers incorporate additional shielding to prevent the occasional EMP?

It probably affects a specific chip Apple are using that may not be present in the Androids.

Since that's what the article says ... I'm gonna say you're right

If the issue were specific HF then it could be a geometric feature.

Am I the only one hoping that exposure to helium made Siri sound like a chipmunk?

Anybody can provide a reason why SiT1532 wouldn't be hermetically sealed? They are talking about high accuracy, intuitively it would seem that if helium affects it this badly, then it would be susceptible to some atmospheric pressure changes (unless the seal worked against air but not helium).

They do have a strong hermetical seal on them, but the older ones used by Apple are still susceptible to “small gas molecules”.

They must have some seal in place and fortunately our air is Nitrogen, O2, and a little bit of Argon. These can’t get through the seal! Helium is only found in minuscule amounts naturally and apparently this concentration is so low it doesn’t matter.

Helium is special because is it has the smallest kinetic diameter of all the noble gases. You can compare its diameter to other gases here: https://en.wikipedia.org/wiki/Kinetic_diameter#List_of_diame...

Helium is frequently used in leak tests since it has a way of working through even the tiniest of leaks. Elemental Hydrogen is of course smaller, but I believe you only find Hydrogen as H2 which is a larger molecule than Helium.

According to that table, Helium is 260, and water is 265, and there are a few more under 300.

Does that mean that water (in some form) also acts like helium and would be able to get through that seal?

I think the answer is that water has polarity! Though we’re definitely hitting my chemistry knowledge limit...

While water’s overall charge is neutral, its charge isn’t distributed symmetrically ans tbis makes it a rather polar molecule. This means part of molecule have different charges which leads to attraction to other water molecules thanks to van der waals forces. Basically water naturally clumps up and won’t squeeze through tiny holes even if it’s kinetic diameter would technically allow it. (Though I believe very high pressure can force it through)

Water’s polarity is what causes surface tension and droplets! For comparison, gasoline is relatively nonpolar, though not as nonpolar as He. If you’ve ever spilled some you can see it spread out immediately and avoid the droplet formation and cohesion you’d see with water. Similarly, water tight containers might not be gasoline tight. (but don’t test this out...)

To correct my comment from earlier: Helium is special because of its small kinetic diameter AND because it’s naturally found in a monoatomic and nonpolar form, as are all noble gases. This lack of polarity leads to minimal intermolecular attraction that would cause clumping and limit flow.

(I found a reference that helium can be measured flowing through a 1.0nm hole, albeit at a very low rate. I wonder how close to the 0.260nm kinetic diameter a hole can get for He to still flow)

Presumably it can still pass through if the hole is smaller than 0.26nm!?

I really have no idea...but I don't think so! Or at least if the kinetic diameter is the smallest hole something can fit through it can't?

Helium's is 260pm or 0.26nm so that could be the limit. But the actual atomic diameter has a couple different calculated and observed values from 31pm to 140pm so maybe it could fit through holes around that size? My guess is we don't have the technology to make a hole of precisely that size or even measure a single He atom passing through such a hole. Would probably have to find a real expert to know if it's theoretically possible.

Sealing against Helium is vastly more difficult than sealing against air, as air is made out of molecules of rather large atoms, while Helium gas consists of single small atoms. That is why divers watches often have a "helium escape valve". The watches are sealed against high pressures of water or air. But when worn in pressure chambers where divers live on a mix of high pressure helium and oxygen, the helium gets into the watch. When depressurizing at the end of the pressure chamber time, the helium pressure could blow the watch crystal from the watch if not released by the escape valve. For a similar reason pilot watches have special fastening of the watch crystal, so that underpressure doesn't lift it off.

Those helium escape valves are just for marketing overpriced toys to pretentious wannabes. Most working saturation divers haven't used fragile, expensive mechanical wristwatches for decades now.

The seal works against air but not hydrogen or helium because the molecules are so small they'll diffuse through pretty much anything.

It's really hard to contain helium. It'll leak through pretty much any solid material.

is mylar special? a good mylar balloon can float for weeks

It's not special, just less porous compared to latex. Mylar balloons still lose gas after time.

It's the aluminium on the mylar.

>(unless the seal worked against air but not helium).

That is exactly the case. From the article, helium (and to a lesser degree, hydrogen) have very very small molecules and are able to slip past very small imperfections in hermetic seals.

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