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Comment by varenc | Hacker News Reader

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.

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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.

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

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, with iPhones!

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.

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.

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

> 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?

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.

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.

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.

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.

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.

https://www.ors.od.nih.gov/sr/dohs/Documents/ProtocolOxygenM...

http://www-group.slac.stanford.edu/esh/eshmanual/references/...

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”

https://www.nursingcenter.com/journalarticle?Article_ID=1617...

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.

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