Gas Chlorine?

[Rattus Suffocatus]

I guess, the point that RS wanted to make is, that boiling liquid nitrogen can quickly create dangerous levels of nitrogen gas, decreasing the oxygen concentration in a confined space. At room temperature, 1L of liquid nitrogen will eventually turn into about 700L of nitrogen gas. In that sense, it is toxic - whether you die by lack of oxygen or actual poisoning is bit of a technicality. The other danger is blocked overpressure valves, particularly in combination with failing insulation of a tank - if the overpressure created by a boiling liquid can't get released, a tank can eventually explode.

At Uni, I used to work with liquid nitrogen. The one golden rule we had (I am sure, that working with liquid nitrogen in a corporate environment would involve many more rules...) was to never ever be in an elevator together with a tank of liquid nitrogen (or other cryogenic liquids). If that elevator get's stuck, you're in serious trouble.

Yeah.... the effect is the same. Of course I know that the atmosphere is mostly nitrogen. Unfortunately the reflex of sensing asphyxiation basically works on sensing CO2 or burning like with chlorine. Whereas Nitrogen is obviously not toxic in and of itself high concentrations displacing oxygen are, and you generally get the "boiling frog" analogy since there is little natural sensing of this situation.

I thought that was implied when I simplified the sentence a bit. I am stressed out and tired -- but I should have known better with this crowd!

Inert gas asphyxiation - Wikipedia

en.wikipedia.org

 

[JoyfulNoise]

Fun fact: The record "depth" for a breathing gas mix was set in a pressure chamber (so not an actual dive), something like the equivalent of 2300 feet. The gas mix used was hydrox, as in hydrogen-oxygen. For obvious reasons, besides in a couple of experiments this mix is not used for breathing gas...

Meh, hydrox … no biggie. Just don’t try to light up a cigarette and it’ll be fine.

 

[JamesW]

The reason they use helium instead of nitrogen is because nitrogen gets dissolved too much in your blood when you are under pressure and the nitrogen comes out of solution when the pressure is reduced.

This causes “the bends”.

 

[Newdude]

Meh, hydrox … no biggie.

Anyone else remember hydrox as the OG Oreo cookie that was 10X better ?

 

[Rattus Suffocatus]

In high school we did the test tube thing with the natural gas having it pop at the end. The teacher encouraged us to try hydrogen (there is your hydrox more or less). Slightly bigger pop when the atmospheric oxygen got in there. I managed to dig up a piece of calcium carbide.... I think the hole in the suspended ceiling panel is still there. Ah, yes Oxyacetylene sure had more oomph... The teacher really wasn't impressed.

I used to do a bit of electrolysis as a teenager producing hydrogen and oxygen. Been temped to capture some of the gas coming out of the SWCG but, alas, I am sort of an adult now.... I did a lot of fun experiments with Hydrogen and Oxygen....

I almost became a Chemical Engineer instead of a EE. I do regret not studying more of that regardless. I really missed out not taking Organic Chemistry. As a EE I took darn near everything that all the other engineers took though, and the physics majors and math majors did as is was....Maybe I wouldn't have been stuck writing software most of my life.... oh well....

 

[mguzzy]

I really missed out not taking Organic Chemistry.

This statement made me spit out my coffee...

I mean enduring two semesters of O-Chem convinced me that I should either end my college career with one leap off the Campanile or major in Physics. I choose the later.

 

[jseyfert3]

Meh, hydrox … no biggie. Just don’t try to light up a cigarette and it’ll be fine.

The percentage of O2 used in the mix is really low, 4% by volume or less. Let's see, at 2300 feet is 68 ATM. You only need a partial pressure of 0.2 ATM of O2 (and more than ~1.3 ATM of O2 sustained will start causing seizures, which is why deep diving gasses will suffocate you at the surface of the water), so 0.02/68 = 0.3% O2 by volume (with a max allowable O2 of 1.9% by vol), assuming I didn't miss something obvious and my calculations are correct. Hydrogen's UEL is 94% in O2, so at atmospheric pressures 0.3% O2 in 99.7% H2 is certainly not explosive but I'm not sure if explosive limits depend on solely the volume or the partial pressure of O2...

The reason they use helium instead of nitrogen is because nitrogen gets dissolved too much in your blood when you are under pressure and the nitrogen comes out of solution when the pressure is reduced.

This causes “the bends”.

My understanding is that's not the main reason it's used. Under enough pressure all gasses have a narcotic effect on humans, originally called the "rapture of the deep". Nowadays this is often called nitrogen narcosis, since bigger molecules have a stronger effect and compressed air is 78% nitrogen, so nitrogen is the primary cause of narcosis in recreational diving. This limits the depth you can dive with nitrogen if decompression time is not a concern, and a compressed air mix has narcotic effects that start kicking in around 80-100 feet or so, varying some from person to person. Much deeper and most people will loose the ability to function completely, doing crazy things like pulling out their mouthpiece because they think they can breath water, hence the old name rapture of the deep.

Helium is much smaller and has drastically reduced narcotic effect for a given pressure, allowing dives approaching 2000 feet on a pure helium/oxygen mix. Hydrogen has even less narcotic effect, hence it's use to a record setting effective depth of 2300 feet in a pressure chamber. You can't go any smaller than hydrogen though, and you need a high enough partial pressure of oxygen to live so you can't eliminate all narcotic effects of breathing gasses under pressure.

I got PADI Open Water certified a few years ago, went full geek mode reading about all things diving related, and only dived a couple times... But hey, useful info for random internet threads!

 

[mguzzy]

Has anyone actually tried mixed gas diving or at least breathed it... its just weird.

One of the coolest classes I did as an undergrad was getting certified to dive. I took both the basic and advanced classes and got an Advanced NAUI cert out of it and half of what I needed if I wanted to get an instructors cert. It came in handy later when I did grad school in Marine Science.. but I digress. The advanced class was a blast we did all kinds of diving things, for 10 weekends out of the 15 week semester. Night dives, deep staged dives, search and rescue dives... all in Monterey Bay. We got exposed to whatever our instructor had access to. But it was an upper division PE class.. and what pray-tell do you do in an upper division PE class.. well you have to write and present a term paper. .. So I did mine on the physics of mixed gas diving. Most of the people did something like a bio on Jacques Cousteau and the presentations were like high school book reports. But mine had charts and graphs and equations and all kinds of coolness. I did my presentation on the poolside chalk board that is usually used for game strategy by the water polo team. You know that moment in a presentation when you know you have lost your audience. I opened by telling them they shouldn't use the dive tables and should instead use this equation. All I got was blank stares, it only took 30 sec.. But I figured that was the point of the presentation, right? ... well except for one guy who was an engineering major... Our instructor was a crusty old dude that was on the dive teams that disarmed the left over bombs in Truk lagoon. Boy the stories he had to tell... He just nodded, cause his ear drums were toast long ago.

Helium is much smaller and has drastically reduced narcotic effect for a given pressure, allowing dives approaching 2000 feet on a pure helium/oxygen mix. Hydrogen has even less narcotic effect, hence it's use to a record setting effective depth of 2300 feet in a pressure chamber. You can't go any smaller than hydrogen though, and you need a high enough partial pressure of oxygen to live so you can't eliminate all narcotic effects of breathing gasses under pressure.

So yeah, that is essentially true. He has a different partial pressure, and a higher rate of tissue desaturation. So the time between dives is reduced as well.

I finished off my presentation with a Martini, shaken not stirred.

 

[Rattus Suffocatus]

I really would have like to learn the material in the O chem classes, tho. I realize it's hard, but so were the higher level solid state physics and EE courses.... That's why they pay us the big bucks, right? I suppose if I would have audited a class it wouldn't matter if I failed it, right?

 

[Vickery]

They didn't name this "The Deep End" for nothing

 

[red-beard]

Nitrogen does dissolve in water, but not much. Look at the solubility charts for CO2 and N2 in water, even under pressure.

 

[Rattus Suffocatus]

They didn't name this "The Deep End" for nothing

You love it, and you know it.