Technical Diving Webinar with John Chatterton

[hobodiver]

I am learning more every second tonight. So eliminating the Nitrogen is mostly about eliminating the nitrogen narcosis, not the deco sickness element, right?

That's one reason. Helium is also much less dense than Nitrogen, so it breaths easier at depth.

There may be other reasons as well.

One of the drawbacks to Helium is that it's expensive. Another reason to use a rebreather.

 

[hobodiver]

did you run the dive on OC or on CCR?

As I mentioned, I was just playing around w/iDeco (the iPhone/iPod touch software) and examining the difference in deco times. It was configured for OC.

 

[HowardE]

As I mentioned, I was just playing around w/iDeco (the iPhone/iPod touch software) and examining the difference in deco times. It was configured for OC.

Deco time on a CCR is considerably less, as you maintain a constant PO2 the entire dive.

 

[BoomerNJ]

That's one reason. Helium is also much less dense than Nitrogen, so it breaths easier at depth.

There may be other reasons as well.

One of the drawbacks to Helium is that it's expensive. Another reason to use a rebreather.

I also heard somewhere that there is a finite supply of Helium, so eventually we are going to run out... I'm not sure where I heard that, but I believe it related to the expense of it as well..

 

[hobodiver]

Deco time on a CCR is considerably less, as you maintain a constant PO2 the entire dive.

Turning on the CCR option, and using a setpoint of 1.2, it shows a total runtime of 168 minutes on air (108 minutes of deco).

A CCR Heliox mixture (80/20) shows a total runtime of 197 min for the same dive (137 minutes of deco).

Wouldn't it be more accurate to say the deco time is less because the PN2 and PHe is lower because you are maintaining a constant PO2?

 

[hobodiver]

I also heard somewhere that there is a finite supply of Helium, so eventually we are going to run out... I'm not sure where I heard that, but I believe it related to the expense of it as well..

Helium is an inert gas, so it doesn't react with anything. Any helium you inhale is ultimately exhaled again and re-enters the atmosphere. Since it's a lighter gas than air (oxygen or nitrogen), it might float to the top of the atmosphere and escape into space. Technically you can produce Helium through nuclear fusion though we haven't quite mastered the fusion thingy here yet.

Edit:
Helium makes up about 0.0005% of the earth's atmosphere. This trace amount of helium is not gravitationally bound to the earth and is constantly lost to space.

http://education.jlab.org/itselemental/ele002.html

 

[Rhone Man]

I also heard somewhere that there is a finite supply of Helium, so eventually we are going to run out... I'm not sure where I heard that, but I believe it related to the expense of it as well..

I think it replenishes itself through radioactive decay, but known reserves are depleting. Hopefully they will find some new big fields soon and bring the cost down (although I understand it is only collected as a by product - not as a resource in itself).

 

[Chatterton]

HD,

If as you say, the goal is to be a rebreather diver then you are required to take Advanced Nitrox, as far as I know. Since there are a bunch of manufacturers and they all write different prerequesites, there could be an exception some place, but in general you need AN?

Regardless, you really do benefit from taking the Advanced Nitrox course. Not required is the Deco Procedures course, which I would recommend. The fundementals of deco OC will pay off later for most divers whether they want to be deco rebreather divers or not.

As for Extended Range it is great diving experience, it is my opinion that if you are sure you want to go rebreather, you should probably get to it sooner rather than later.

Cheers


JC

John,

If the ultimate goal is to move to a rebreather, do you still think that the ER class is useful? Or maybe I should say, is it necessary?

Honestly, I'm not sure I have any desire to dive to 300 ft. In fact, I'm not sure I can really think of anything I'd want to dive @ 200 ft. Maybe the Monitor.