Hydrox

[Rick Murchison]

detroit diver once bubbled...
Hydrogen is also
being investigated as a substitute for helium in deep-sea diving applications below 1,000 feet.
---

That is interesting. The Hindenberg comes to mind.

Oxygen content of deep diving mixes is low enough for the mix to be safe with hydrogen; hydrogen is not suitable at shallower depths where the oxygen concentration would be high enough to support combustion.... where, as you say, the Hindenberg comes to mind.
Rick

 

[SamDiver14]

In the effort of precision not argumentation,

Oxygen content of deep diving mixes is low enough for the mix to be safe with hydrogen; hydrogen is not suitable at shallower depths where the oxygen concentration would be high enough to support combustion.... where, as you say, the Hindenberg comes to mind.
Rick

In this situation the oxygen would be the limiting reactant but a lower level would not mean combustion is not possible. It only means that a complete combustion would not occur. Only one molecule of oxygen is required for combustion, it is just that the reaction would stop when the O2 ran out. Anyway, Rick, you are right, the risk level is really low, but technically combustion is possible wherever any molecule of oxygen is present.
Sorry, like I say, I am not being argumentative.
Sam

 

[Rick Murchison]

In the effort of precision not argumentation,

Oxygen content of deep diving mixes is low enough for the mix to be safe with hydrogen; hydrogen is not suitable at shallower depths where the oxygen concentration would be high enough to support combustion.... where, as you say, the Hindenberg comes to mind.
Rick

In this situation the oxygen would be the limiting reactant but a lower level would not mean combustion is not possible. It only means that a complete combustion would not occur. Only one molecule of oxygen is required for combustion, it is just that the reaction would stop when the O2 ran out. Anyway, Rick, you are right, the risk level is really low, but technically combustion is possible wherever any molecule of oxygen is present.
Sorry, like I say, I am not being argumentative.
Sam

Of course you're being argumentative.
If you put a jar over a burning candle, the candle will go out. There will still be a small amount of oxygen in the bottle, but it will be below the amount needed to "support combustion." Sure, if you could somehow bring that remaining oxygen into contact with the wax and provide enough heat down at the molecule-to-molecule level you could get oxidation (burn) one molecule at a time, but it won't happen naturally. The risk level is below "really low" - it's not just a matter of hydrogen and oxygen, but hydrogen and oxygen and heat. Once a mix is below the sustained combustion level any attempt to burn it just fizzles. Sorta like having a pile of uranium below critical mass... you can pound it all day but nothing will happen.
Rick

 

[BigJetDriver]

Of course you're being argumentative.
If you put a jar over a burning candle, the candle will go out. There will still be a small amount of oxygen in the bottle, but it will be below the amount needed to "support combustion." Sure, if you could somehow bring that remaining oxygen into contact with the wax and provide enough heat down at the molecule-to-molecule level you could get oxidation (burn) one molecule at a time, but it won't happen naturally. The risk level is below "really low" - it's not just a matter of hydrogen and oxygen, but hydrogen and oxygen and heat. Once a mix is below the sustained combustion level any attempt to burn it just fizzles. Sorta like having a pile of uranium below critical mass... you can pound it all day but nothing will happen.
Rick

Uncle Ricky,

Very nice common-sense and plain-language explanation!!

Every once in a while, someone gets fired up about this hydrogen issue with diving. Comex worked with it in the 80's for saturation diving, and found that the headaches outweighed the advantages by a long shot.

If a diver is worried about the rising cost of helium, he or she should get a rebreather. You use SO much less of the gaseous gold it's amazing!!! :11:

Nice hat, by the way!

 

[pipedope]

Remember that this is going to be bell supported diving.
The bell has to be able to support the divers for a considerable time without help from the surface so now you have added lots of complexity, gear and weight to the bell.

 

[SamDiver14]

Well technicalities are my specialty, by nature of my chosen profession. Rick, you are absolutely right. When a candle is covered it goes out and all of the limiting reactant is not used. The same way that a power plant produces only about 60% of the energy available in the coal. Also, in diving under the conditions that produced this current tangent, there is not favorable conditions for combustion. Will you grant me only one point? Where a molecule of oxygen is present combustion "can" occur. But in the common sense, non technical, everyday use sense, it just ain't gonna happen. Thanks,
Sam

 

[BigJetDriver]

Uncle Ricky,

Nice hat, by the way!

Uncle Ricky,

It is indeed a nice hat, but I forgot to ask what all that gray schmutz is that's on your face---he-he-he!!!

 

[DA Aquamaster]

There was some experimentation with hydrox for deep dives in the 50's or 60's. It worked well enough but at the depths where it was tested the O2 content had to be kept below 4% to preclude the potential for a fire.

It also required the diver to switch to a low 02 interim mix before switching to the hydrox at depth to ensure the 02 content in his lungs was below 4% before switching to the hydrox. Big PITA and beyond the practical for anything other than a well funded and equipped commercial operation.

As long as the PPO2 is low enough, a fire cannot be sustained. NASA used to fly in a 100% O2 environment at 1/3 Atm. It was plenty safe despite the high 02 level and actually safer in flight (for other reasons) than a normal air environment. Where it was a problem was on the ground where 100% O2 at 1 atm was literally an accident waiting to happen (Apollo 1). After that fire, NASA used a 21/79 mix on the ground and then vented it overboard during ascent and replaced it with 100% O2 for the remainder of the flight.

 

[wedivebc]

Well technicalities are my specialty, by nature of my chosen profession. Rick, you are absolutely right. When a candle is covered it goes out and all of the limiting reactant is not used. The same way that a power plant produces only about 60% of the energy available in the coal. Also, in diving under the conditions that produced this current tangent, there is not favorable conditions for combustion. Will you grant me only one point? Where a molecule of oxygen is present combustion "can" occur. But in the common sense, non technical, everyday use sense, it just ain't gonna happen. Thanks,
Sam

Actually according to the MSDS sheet on hydrogen the lower explosive limit (LEL%) is 4% and the upper explosive limit (UEL%) is 74.5% . That is the percentage range of hydrogen in air that will supprt combustion.

cheers,

 

[SamDiver14]

Actually according to the MSDS sheet on hydrogen the lower explosive limit (LEL%) is 4% and the upper explosive limit (UEL%) is 74.5% . That is the percentage range of hydrogen in air that will supprt combustion.

cheers,

Agreed, but under lab conditions every molecule of O2 can be combusted both above and below the explosive limits. A good example of what I am refering to is the same reason we have regs O2 cleaned. While under most conditions combustion is unlikely a situation can be created where virtually everything is combustable. But as I posted earlier, any of the condition we are refering to would never result in combustion of any kind. That, however, does not mean to imply that laboratory condition can not be created where such combustion is possible. The key here is lab conditions vs. real conditions. Rarely do the two ever meet.
Sam