To use argon bottle or not?

[RainPilot]

I find I get around 3 dives in that range (51m) out of an AL6.

My rule for it is simple. Any He in back gas? Then use the AL6

I usually transfill it before a day of diving with 32% (or whatever I have available with no He - sometimes it's 50%) or in some cases, driven off a deco bottle at depth.


_R

I seem to remember some sort of argument around using rich mixes for a drysuit some time back. Is that no longer a thing?

IIRC the gist was that some undergarments etc made a fire risk in O2 saturated clothing during and post dive.

 

[Diver0001]

sounds like one for Mythbusters ☺

R..

 

[steady1570]

If you already have a suit bottle and you can see diving with higher fractions of He / colder water in your future then why not get into practice using it now, standardised kit etc? A separate suit bottle also genuinely gives you a redundant buoyancy source. And finally practicing swapping hoses over gives you something to do on deco

-Mark

 

[Diver0001]

I seem to remember some sort of argument around using rich mixes for a drysuit some time back. Is that no longer a thing?

IIRC the gist was that some undergarments etc made a fire risk in O2 saturated clothing during and post dive.

On second thought, one or two things do come to mind that could make this possible.

[begin theory spinning]

In order to have a fire you need to have oxygen, a heat source hot enough to ignite a fuel and a fuel. Cases of spontaneous combustion can be been achieved with some metals like titanium under the right conditions but that's outside the scope of a discussion about an undergarment catching fire.

So right away when you're putting a high nitrox mix in your suit you have oxygen and a fuel source, which is the undergarment itself. All that is missing is a heat source hot enough to start a fire.

Two things come to mind that could potentially give the heat.

One is a malfunctioning electrically operated thermal vest. It's attached to a battery and it's full of wires so potentially I could see it sparking a fire if some kind of a short circuit were to happen.

The other is if the diver unwittingly used the kinds of hand warmers in the vest that react with oxygen. Under pressure they get much hotter as the partial pressure of oxygen goes up and if you were to put in a high nitrox mix on top of that then the heat would go WAY up.... maybe hot enough to start a fire. I know there have been cases of divers being burned by not understanding how hand warmers work in the past so this idea seems somewhat plausible to me if the temperature could go high enough.

[/end theory spinning]

I guess this could be an argument for putting argon in the vest, particularly if the diver were using a battery powered thermal vest. The hand warmer thing is more of a "Darwin" issue that would hopefully only end in something they would have to explain to their spouse.

R..

 

[w3dge]

I remember reading of a case not so long ago of some chap who had serious burns due to Oxygen reacting with a chemical-based suit heater. I believe that was chemical burns though.

An obvious source of ignition in my mind would be static sparks from nylon-based under garments.

 

[Diver0001]

An obvious source of ignition in my mind would be static sparks from nylon-based under garments.

Not enough heat. 100% sure of that. A discharge of static electricity contains far too little energy to generate the heat required to ignite an undergarment. What happens in a static discharge is that a flow of electrons happens from A to B, usually using the human body as a sort of "ground" or "capacitor", therefore causing an electrostatic discharge with a measurable voltage that can be quite high but with a current of almost zero. The discharge also takes place very fast so the amount of energy generated is normally expressed in milijoules. The reason you feel it so well is that our nervous systems also work on these levels of energy, so it can feel worse than it really is. However, in terms of "heat", static electricity creates very little heat.

To put this another way, you can see voltage as how fast the electrons are moving and current as how many electrons are moving.

To use an an analogy, think of a garden hose. Voltage is how fast the water comes out of the hose and current is the volume of water that comes out of the hose. If both are high then the stream of water is powerful, maybe even powerful enough to cut metal. If the water comes out very fast but it's only a tiny little stream a few molecules wide then you might have to concentrate to even feel it.

That second thing is static electricity.

So in order to boil a liter of water with static electricity, or to start an undergarment on fire, you would need a sustained static discharge of a HUGE amount of time (I'm going to spare you the math here but let's just call it a HUGE amount of time) to create enough heat for our scenario.

R..

 

[PfcAJ]

Use the suit inflation bottle.

Imagine a flooded suit, delayed pickup time, extended deco, etc. anything that's going to make you colder isn't stacking the deck in your favor.

Additionally, using a deco bottle is ill advised as that requires having a bottle turned on past its MOD. Having everything turned off is one of your safeguards against breathing the wrong gas. With one deco bottle it's easy to skip over this, but build strong habits and procedures starting in the beginning.

 

[kensuf]

A 6ft bottle will be plenty of drysuit gas. I did two dives to 270' this weekend and used a 6ft bottle for both of them. You're not going to run out of drysuit gas on a 150' dive unless you're constantly filling and dumping your suit.

The thermal stuff is real. Helium will make you colder. It's not worth it.

Some people believe that filling a drysuit with trimix can increase your susceptibility to skin bends. I have no opinion on this, except that there are plenty of reasons NOT to use trimix in a drysuit that I wouldn't bother trying to test this theory.

 

[stuartv]

A 6ft bottle will be plenty of drysuit gas. I did two dives to 270' this weekend and used a 6ft bottle for both of them. You're not going to run out of drysuit gas on a 150' dive unless you're constantly filling and dumping your suit.

Thanks for that confirmation.

The thermal stuff is real. Helium will make you colder.

I started typing a response that was a question. As I typed it, I realized what the answer is.

I will use my inflator bottle.

Thanks!

 

[Akimbo]

Argon looks a little better than dry compressed air when you just look at the theory. Unfortunately the theory gets shot to hell inside a drysuit because perspiration makes humidity very high so vaporous water conducts heat so much faster it cancels out most of Argon's advantage.