Comment by gok

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.

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?

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.

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.

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/...

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.

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.

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.

Occam's razor.

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?

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

https://en.wikipedia.org/wiki/Trimix_(breathing_gas)

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.

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.

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.

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 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.

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.