Ommiting Nitrogen on Deco

[nova]

At what point can you handle the helium coming out of solution shallow without it being dangerous? 20ft? 10ft? surface? We do the same with nitrogen all the time. Pop out of the water and still be subject to offgassing hours later.

Because Helium offgasses quicker, we "should" be able to get rid of more of it in the shallow stops than we could nitrogen. Which is the reason for using it in the first place.

I know the WKPP guys have played with this a bunch. I am trying to dig a bit deeper into the why's of it.

your scarin me again, the two uses of helium are to think clearly and to go deeper. when adding helium to ANY breathing gas you ADD time to the deco profile. That's the trade off for a clear head at a deep depth. If your goal is to clean out the inert gas then don't add a faster gas to the mix, You're right about it lowering the amount of N2 in the body, but you replace N2 with helium, and helium will bend you faster and harder then N2 could ever do.

Don't be such a big fan of the WKPP project, they have been known to cover up some mistakes (but you didn't hear that from me)

 

[PerroneFord]

I try to read information from ALL sources and distill what I think is right. The WKPP divers have pushed diving science in many instances, and have exposed problems in their own and other methodologies. I am not saying what they say is gospel (ratio deco comes to mind) but it has been a good source for some info. As has been stuff from countless other places.

Don't let me scare you. I am hearing what you are saying, and I only took exception to a single statement you made. We agreed on all other points.

What's your experience with accelerated stops?

 

[nova]

I try to read information from ALL sources and distill what I think is right. The WKPP divers have pushed diving science in many instances, and have exposed problems in their own and other methodologies. I am not saying what they say is gospel (ratio deco comes to mind) but it has been a good source for some info. As has been stuff from countless other places.

Don't let me scare you. I am hearing what you are saying, and I only took exception to a single statement you made. We agreed on all other points.

What's your experience with accelerated stops?

well let just say, that I know that filling a tank with half air and half helium won't give you 21/50

 

[ScubaSixString]

At what point can you handle the helium coming out of solution shallow without it being dangerous? 20ft? 10ft? surface? We do the same with nitrogen all the time. Pop out of the water and still be subject to offgassing hours later.

Because Helium offgasses quicker, we "should" be able to get rid of more of it in the shallow stops than we could nitrogen. Which is the reason for using it in the first place.

I know the WKPP guys have played with this a bunch. I am trying to dig a bit deeper into the why's of it.

Lets look at it like this. Diving on air (or a nitrogen based blend), you have an NDL of 60min (for example). You dive a bottom time of 60 mins and return to the surface.

Assuming all else is as it should be (ie conforms to the deco models) if you keep your rate of ascent below 30 ft/min you should be ok. What happens if you come up at 90ft/min? (ignore AGE/pneumothorax/etc for the time being and focus on the risks of DCI)

Why?

The answer, as i understand it, is that you risk of getting an N2 bend increases drastically. The gas comes out of the tissues too quickly.

Helium comes out even quicker.

as for the shallow depths. Think of this. Sitting at your computer right now (assuming you've been breathing air at around 1ATA for the last 24 hours) the nitrogen in your body is in equalibrium with the ambient atmosphere. (79% n2, for the sake of arguement). What is the helium content? Probably negligable.

If you had been breathing helium blends at 20 ft only, and ascended slowly, you should be fine ( i would think).

But a 66 ft ascent with a N2 load on the body and a 66ft ascent with a He load are not the same. You have MUCH more helium to offgas to reach surface equilibrium than you do N2 (you're kinda given a credit here, because your breathing gas on land has alot of n2 in it to begin with)

Where would you be safe? It depends on your profile. While you are correct that breathing Trimix 50/40 will offgas more N2 than nitrox 50/50, you have added a problem of ONgassing He. And that has to be dealt with. And He requires slower acsents (longer deep deco stops) than N2, to my knowledge.


But i may be missing the question. What is it specifically that you are asking?

 

[nova]

Lets look at it like this. Diving on air (or a nitrogen based blend), you have an NDL of 60min (for example). You dive a bottom time of 60 mins and return to the surface.

Assuming all else is as it should be (ie conforms to the deco models) if you keep your rate of ascent below 30 ft/min you should be ok. What happens if you come up at 90ft/min? (ignore AGE/pneumothorax/etc for the time being and focus on the risks of DCI)

Why?

The answer, as i understand it, is that you risk of getting an N2 bend increases drastically. The gas comes out of the tissues too quickly.

Helium comes out even quicker.

as for the shallow depths. Think of this. Sitting at your computer right now (assuming you've been breathing air at around 1ATA for the last 24 hours) the nitrogen in your body is in equalibrium with the ambient atmosphere. (79% n2, for the sake of arguement). What is the helium content? Probably negligable.

If you had been breathing helium blends at 20 ft only, and ascended slowly, you should be fine ( i would think).

But a 66 ft ascent with a N2 load on the body and a 66ft ascent with a He load are not the same. You have MUCH more helium to offgas to reach surface equilibrium than you do N2 (you're kinda given a credit here, because your breathing gas on land has alot of n2 in it to begin with)

Where would you be safe? It depends on your profile. While you are correct that breathing Trimix 50/40 will offgas more N2 than nitrox 50/50, you have added a problem of ONgassing He. And that has to be dealt with. And He requires slower acsents (longer deep deco stops) than N2, to my knowledge.


But i may be missing the question. What is it specifically that you are asking?

I think he's asking if being fubar bent really hurts or is it an urban myth. I'm just joking perronford

 

[ScubaSixString]

I think he's asking if being fubar bent really hurts or is it an urban myth. I'm just joking perronford

I had a tequila bend one time....is that close

 

[nova]

I had a tequila bend one time....is that close

did ya eat the worm? LOL because you can off gas tequila better than Mescal IMHO

 

[PerroneFord]

I think the thread has run it's course. Thanks gentlemen for your participation. That was nice to kick around.

 

[ScubaSixString]

I think the thread has run it's course. Thanks gentlemen for your participation. That was nice to kick around.

I for one am not trying to argue. I just don't quite understand. Did you try running V-Plan with o2 for both the N2 based deco and the one on Heliox?

That would be a "fairer" representation of the two than one using nitrox with no o2 and one using heliox with o2. IMHO

 

[nova]

I think the thread has run it's course. Thanks gentlemen for your participation. That was nice to kick around.

Looking through your past posts I've noticed that you are not even nitrox certified yet. I think it's a little early for you to be doing deco dives, much less diving with helium. Mixed gas is not a joke, so to use an old expression " no soup for you"

slow don't some, the world will be there when you're ready for tech diving