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Comment by nradov | Hacker News Reader

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.

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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.

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

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