Not accelerating decompression?

[DCBC]

What is extended range?

Extended Range is often referred to as Deep Air (as Rhone Man has already stated). What is meant by this however is a matter of perspective. As far as the parameters of extended range diving, the answer can only be given from a certification agency perspective. These agencies however don't always agree as far as the maximum depth of extended range diving. As the recommended maximum depth for sport diving is set at 130' by most agencies, I think it's fair to say that extended range is diving on air past 130' to the maximum depth recommended by the Deep Air program that's taken.

 

[fdog]

What Lynne said.

Personally, I don't run very aggressive deco schedules, so I tend not to carry stages and just deco on air (plus any kind of nitrox is hard to get ahold of here, much less super rich nitrox). The benefit of trimming my 10 minute deco to 7 minutes is just not worth humping a side bottle around.

If I was doing 30+ minutes deco, I might reconsider...

There's more than just time to consider, though. For example, taking oxygen (in addition to 50%) along may only buy me 6 or 8 minutes; but the hassle of two bottles is worth it for the nice clean feeling when getting out of the water.


All the best, James

 

[lowridersvt]

I have very little experiance with deep air dives maybe 10 to 150 to 200ft range since i turn into a fool around 130ft on air.

But this is the way i look at it if your doing a deep air dive to 170 for 30 min Using a 50% mix at 70ft will spike you po2 to about 1.55 and will drive out unwated gas much faster than air and should still be considered accelarated decompression.

The down side to planning your deco with 50% as air mostly on a very deep air dive your oxygen clock (cns) will be getting near you limit for the dive.Could cause some issues oxygen toxicity

Buy switching to any botle at 70 ft you are saving back gas for any emergencys so having those spare bottles on hand do help allot.

But doing a deep air dive with out 02 to clean out your slow tissues at 20 ft is a crap shoot i would never do that up here in cold water

And btw most o2 analyzers are +/- 1% anyways so 48% to me is still considered 50%

 

[Red Sea Shadow]

The IANTD for one teaches that 50% is the minimum for accelerated deco.

Thanks. That's what I was looking for; where did they get that from!

 

[Diver0001]

I don't know but tables are not like computer programs. They're tested with certain parameters and if you don't follow those parameters there's not much you can do to adjust and still be on the table.

If you understood enough of the theory you could pad by gut feeling but it's not very scientific.

R..

 

[Red Sea Shadow]

Well the people I know who adopt this opinion (less than EAN50 is not accelerating deco) are using computer programs. Although the numbers are very obvious, they still opt for running the plan as if they're decompressing on air. May be IANTD standard you mentioned is the reason behind that.

 

[Diver0001]

It could be but if you have a computer that can handle all the gasses you're diving with then it would stand to reason that you don't have to follow the table so literally.

What your friends are doing has the advantage, however, of being foolproof assuming their dives aren't too ridiculous. In some scenarios using air for a bottom gas 50% can cut more than an hour off of your hang time (if you could even make the dive) but in most doable dives you're talking about 10-15 or so minutes extra at most.

To my way of thinking unless their dives are ridiculously long (or deep) there's nothing really wrong with what they are doing. They'll do longer than necessary deco times but if they don't mind that then their deco will be thorough and there's certainly something to be said for that, especially if they're working as dive guides and making 500 dives a year.

R..

 

[liuk3]

What used to be called "deep air" in less politically correct days:

International Training :: Get Certified :: Extended Range Diver :: English

Class for diving air to 180 ft. if I understand correctly?

 

[battles2a5]

I think that's a pretty foolish way to run deco. If you are not going to count the gas towards your deco, why bother carry the gas? Any gas you take down below it's MOD should be treated like a loaded gun. If you aren't getting any benefit from the gas, leave it on the boat.

As others have stated, gas mechanics aren't going to change if the gas is less than 50%. There are essentually 2 ways to off-gas; pressure gradients (ascent) and gas partial-pressures (mixes). Switching gases along your ascent combines both and accelerates decompression. On deeper dives, where travel gases and multiple deco gases are used, you will likely have a couple that are less than 50%. If you ignored them in your deco calculations you would be in the water for a really, really, long time.

I wonder how are these guys calculating CNS? If they are treating their deco gas like BG, they should at least calculate CNS based on the actual gases and exposures. Ignoring the benefit of your deco mix is a great way to burn through your CNS clock.