Would you use 50% for inflation with heated undergarments?

[dreamdive]

I am not. Using my rich gas for inflation up to 100 m dives.

 

[tbone1004]

less of a concern with certain designs of vest. The Saanti suits use a cheap woven carbon fiber per all vests except those made by Exo2 and those can short if the carbon is damaged, thus sparking. Unlikely the 50/50 mix will be a problem for the reasons that were mentioned above, mainly the volume of gas in the suit when you start, so I wouldn't worry about it with 50%

 

[andrewy]

faor last 4 years i use heater and 32%. the heater is carbon fiber. it destroys itself at 100 C. to start fire you need a spark. so try not to smoke while diving.
i do have an argon bottle, but still fill it with 32 or air.

 

[kr2y5]

faor last 4 years i use heater and 32%. the heater is carbon fiber. it destroys itself at 100 C. to start fire you need a spark. so try not to smoke while diving. i do have an argon bottle, but still fill it with 32 or air.

Me too, but I think 32% and 50% are not quite the same. If you look at the document @boulderjohn posted, there seems to be something magical happening around 40%. I vaguely remember someone, somewhere quoting some NASA (or some such) study indicating that beyond 40%, in terms of destructive potential Nitrox behaves like O2. ( I may be misquoting so take it with a grain of salt. )

Don't forget the GoPro. I'm just sayin.

Ah, the GoPro has exclusive rights to my left chest D-ring.

This being said, today I needed a video light, and for the lack of a better place, I had to attach it to a deco bottle, on the inside.

A slight tangent, but: how do you feel about attaching stuff to tanks? Entanglement hazard? Bad on principle?

 

[The Chairman]

how do you feel about attaching stuff to tanks

Like your underwear... it depends.

I've seen things clipped off to tanks that seemed to work fine. I haven't done it, but I didn't feel I needed to, either.

 

[Stoo]

That's a lot of stuff to butt-mount, with canister + inflation bottle + equipment pouch all competing for a piece of real estate on my glutes.

Bacon and time my friend. Bacon and time...

 

[Storker]

Me too, but I think 32% and 50% are not quite the same. If you look at the document @boulderjohn posted, there seems to be something magical happening around 40%. I vaguely remember someone, somewhere quoting some NASA (or some such) study indicating that beyond 40%, in terms of destructive potential Nitrox behaves like O2. ( I may be misquoting so take it with a grain of salt. )

Are you thinking about this graph on p.6? It seems to me that the transition is closer to 36% than 40%

I wouldn't say that something "magical" happens around 40%. It's not as if 39% is perfectly safe, while 41% suddenly is just as bad as O2. As always in chemistry and physics, there's a continuum, and - as the cliche says - we draw a sharp black line through an increasingly darker gray area. Now, that sharp black line has been drawn at 40%, probably to have a margin.

On the other hand, 40% at depth isn't the same as 40% on the surface since pPO2 increases with depth given the same fO2. For flammability, pressure has less effect than the pure partial pressure effect, but it has an effect: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070005041.pdf

 

[kr2y5]

Are you thinking about this graph on p.6? It seems to me that the transition is closer to 36% than 40%
View attachment 376865

I wouldn't say that something "magical" happens around 40%. It's not as if 39% is perfectly safe, while 41% suddenly is just as bad as O2. As always in chemistry and physics, there's a continuum, and - as the cliche says - we draw a sharp black line through an increasingly darker gray area. Now, that sharp black line has been drawn at 40%, probably to have a margin.

On the other hand, 40% at depth isn't the same as 40% on the surface since pPO2 increases with depth given the same fO2. For flammability, pressure has less effect than the pure partial pressure effect, but it has an effect: http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20070005041.pdf

Sure, by "magical around" I did not mean "discontinuous at precisely" just that there is a mysterious change somewhere roughly in the ballpark of that number 40% that, for whatever reason, appears to be cited in so many places as an approximate "boundary" (fuzzy, no doubt) between the more safe and the less safe.

What you say about partial pressure is interesting. I don't know anything about flammability, so pardon my ignorance. Just to clarify, are you saying that it's more about partial pressure than % O2 in the gas?

I just looked up Oxygen Hacker's, and found this quote: "NASA concluded that any FO2 over 50% acted pretty much like pure O2", but that these tests were run at atmospheric pressure, so it doesn't necessarily imply much of anything about higher pressures. I thought someone had explained to me where the "40% rule" comes from, but I can't remember, nor can I find the source to reference.

If it's all about ppO2, does it follow that, e.g., if hypothetically, I were to flush my suit completely with the rich gas from the inflation bottle (thus, for a second, ignoring the fact that in reality I may not cycle all the gas in the suit), and also ignoring the questionable wisdom of using my heater at depth if I'm still actively on-gassing, we should be more concerned about:

(a) turning on my heater vest with 32% as inflation gas below 50 feet,

as compared to:

(b) flipping the switch with 50% as inflation gas at around 20 feet,

given same partial pressure about 0.8 (assuming I counted all my fingers correctly).

 

[Storker]

What you say about partial pressure is interesting. I don't know anything about flammability, so pardon my ignorance. Just to clarify, are you saying that it's more about partial pressure than % O2 in the gas?

If you look at the PDF I linked to, you'll see that it's both. Under hypobaric conditions (that's the region the work in the article is about, but I'd be very surprised if things changed drastically under hyperbaric conditions), it seems as if FO2 is the most significant factor, but pressure (IOW pPO2) also plays a role.

And no, don't ask me to give you any clear advice about limits. My post was just based on my general science knowledge; combustion chemistry isn't my specialty
Personally, I'd stick to the 40% limit, but that's not advice in any form and may well be due to my generally low risk acceptance

 

[kr2y5]

If you look at the PDF I linked to, you'll see that it's both. Under hypobaric conditions (that's the region the work in the article is about, but I'd be very surprised if things changed drastically under hyperbaric conditions), it seems as if FO2 is the most significant factor, but pressure (IOW pPO2) also plays a role.

Yeah, ok, maybe I did not have enough coffee this morning yet. Staring at those numbers, it sounds to me like a "safe" fO2 % decreases, but safe ppO2 increases with depth, so it doesn't look like they concluded it to be purely a function of either fO2 or ppO2, and there does not seem to be enough data to extrapolate much since all the tests were around atmospheric pressures. I'm guessing it's, as you said, some nontrivial function of both.

And no, don't ask me to give you any clear advice about limits. My post was just based on my general science knowledge; combustion chemistry isn't my specialty
Personally, I'd stick to the 40% limit, but that's not advice in any form and may well be due to my generally low risk acceptance

You probably know more than I do! No worries, though, I'm not looking for a magical rule of thumb, just looking at it as a free exchange of information and ideas. I don't take anything as gospel. If I blow myself up, I won't blame you