Helium Gas Running Out

[TVguy]

Heard a very interesting report on the ABC about supplies of . I never realised the multiple uses of this gas, and the implications of its shortage (not just for kiddies' balloons). Of particular interest is its use in the manufacture of optic fibre cables made by drawing the glass fibre through all-helium atmosphere to prevent bubbles from being trapped inside, and the implications for the NBN.

[gordon_s1942]

Another use is in the Deep Sea Diving industry mixed with other gas's to eliminate the dangerous condition called the 'Bends' caused by the build up of Nitrogen in the divers blood.

[trash]

Don't panic yet kiddies, the sky isn't falling that fast. While we have natural gas wells we have a source of helium and this doesn't take into account other sources with are currently less viable.
The biggest waste of helium is currently balloons, though if helium was rare, hydrogen would be used. It's something worth conserving, but it's not the end of the world yet.

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Helium in diving doesn't eliminate decompression sickness, it just changes the rules a little.
While nitrogen is commonly responsible for decompression illness, both helium and oxygen can cause the same sort of problems to varying degrees.
Helium isn't primarily used to substitute for nitrogen in diving, it's used to substitute for Oxygen !

Typically divers use air. 21% oxygen and 79% nitrogen.
The body absorbs nitrogen and releases it at a steady rate.
The length and depth of the dive determine how much and how fast nitrogen is absorbed into the body.
This effects the duration of a non-decompression dive, or how long a diver must decompress for after a long duration or deeper dive.

To offset the amount of nitrogen a diver is exposed to, Nitrox is used.
Something like EAN36 is a good example. This is 36% oxygen and 64% nitrogen.
Having less nitrogen extends the non compression dive times, but it makes the maximum bottom depth shallower.

We can see from the above example; why not just get rid of all the nitrogen and the diver can breath 100% oxygen?
The reason for this is Oxygen toxicity. (of which there is two main types). Central Nervous System Oxygen toxicity is the main one.
There are limits to how much oxygen you can be exposed to. The limit is typically 160%. (or more correctly 1.6atmO2)
So if we put a diver on EAN100 (100% oxygen) and send him down, when he gets to 6 metres he will black out and start to convulse.
This is obviously bad.

The human body only uses about 3% of the oxygen we breath, but to get this efficiency we must still breath >20% oxygen. Or more correctly 0.2ppO2.
So the next diving gas used is call TRIMIX. Oxygen, Nitrogen and Helium. Helium offsets the Oxygen since at pressure the body is more efficient with oxygen uptake.
You might find a gas which is 21% O2, 29% He and 50% N2. There are reasons for keeping the nitrogen in the mix because breathing helium as it's own set of problems.

But as a diver gets down to 60m (very few recreational divers get past 30m) normoxic (>20% O2) gases become toxic too.
This is where Hypoxic breathing gases are used. The percentage of oxygen is reduced and displaced with helium. At the same time, nitrogen saturation becomes more of an issue again.
So that to is then displaced with helium. At depths below 60m, Heliox is used. There is no nitrogen in the gas.

If divers are using open circuit dive gear, they chew through huge amounts of gas and if most of it is unbreathable helium, the cost skyrockets.
These days recreational divers using helium prefer rebreathers. Oxygen is added to the breathing circuit by a control computer and carbon dioxide is removed from the circuit
but a Calcium hydroxide scrubber. Inert "dilutent" gas like nitrogen or helium remains in the circuit unused. It's only added when needed as ballast.
So while a diver might use 500 litres of oxygen, his closed circuit rebreather may only add one or two litres of dilutent.
The high cost of a rebreather is quickly offset by the cost of the huge amounts of wasted gas.

[mandc]

We can see from the above example; why not just get rid of all the nitrogen and the diver can breath 100% oxygen?
The reason for this is Oxygen toxicity. (of which there is two main types). Central Nervous System Oxygen toxicity is the main one.
There are limits to how much oxygen you can be exposed to. The limit is typically 160%. (or more correctly 1.6atmO2)
So if we put a diver on EAN100 (100% oxygen) and send him down, when he gets to 6 metres he will black out and start to convulse.
This is obviously bad.

The human body only uses about 3% of the oxygen we breath, but to get this efficiency we must still breath >20% oxygen. Or more correctly 0.2ppO2.

So NASA got around the problem of 100% oxygen in their early space program by reducing the pressure in the capsule? Is this correct?
I think they had to change this setup after the 3 astronauts got incinerated on the launch pad in Apollo 1

[gordon_s1942]

I just meant in my comment that helium is a highly important component in the Diving Industry, actually a bit more important than reducing bubbles in the manufacturing of Optical Fibre and any 'shortfall' of the availability of Helium would seriously impact on that industry.

[trash]

Nar, Helium is already really expensive for diving so it's not used unless they really have to. But when it is used with rebreathers, it's really cheap.
And a lot of work is done with robots these days. It's not a real big concern for them.

Important uses that are a concern is things like MRI machines and anything that uses superconductors.

So NASA got around the problem of 100% oxygen in their early space program by reducing the pressure in the capsule? Is this correct?

Yes, I know that the Apollo missions all used 100% oxygen, so to stop Pulmanory Oxygen Toxicity (the other kind that causes divers problems) they would have had to reduce the
cabin pressure, else the astronauts would have got pneumonia and suffered from serious respiratory problems.
To do this NASA would have had to kept the cabin pressure under about 1/2 atmospheric pressure.

In the shuttles they didn't use oxygen because I've seen astronauts decompressing (off gassing) before a space walk.
They breath pure oxygen in a mask to flush residual nitrogen from their body because the space suit can only offer a limited amount of pressure against the vacuum of space.
Scuba divers sometimes use this same surface decompressing when they need to do a consecutive dive where they want to increase the non-decompression limits.