Skipping surface intervals - DIR or not?

[mwpowell]

When ascending, the PPN2 difference is negative (we go from high PPN2 to lower PPN2)- the bigger the difference the faster rate of offgassing. Therefor, If you want to achieve faster offgassing you'd like to increase the PPN2 difference --> it will *allways* be- no matter what type of dive profile- at the surface.

The best gradient is achieved with 100% O2, and is independent of depth.

Mike

 

[Soggy]

The best gradient is achieved with 100% O2, and is independent of depth.

Mike

Yes, but when carrying only a single deco gas, 50% is a much better choice and will get you out of the water faster every single time because you can open up the O2 and offgassing windows much deeper. The shallow stops then become much less important.

 

[Sideband]

This process of ongassing/offgassing depends on the pressure *difference*. If you dive deeper, the N2 partial pressure (PPN2) difference between tissues and blood is higher --> more N2 goes from blood to tissue.

When ascending, the PPN2 difference is negative (we go from high PPN2 to lower PPN2)- the bigger the difference the faster rate of offgassing. Therefor, If you want to achieve faster offgassing you'd like to increase the PPN2 difference --> it will *allways* be- no matter what type of dive profile- at the surface.

I've not done DIR-F so I apologize if I am posting out of place here, but the above needs a bit of correcting and has nothing to do with DIR. While the rate of off gassing N2 IS dependent on the differential, it is NOT always greatest at the surface. Breathing 100% O2 at any depth will provide the same <greatest> differential no matter what depth because there is no N2 being inspired. This doers not mean it is the best choice but it does counter the previous statement.

Joe

 

[Jai Bar]

OK. 100% O2 is better (err... not really at any depth. I think 100% is also not DIR at depths greater than, say, 6 meters? )

The original question was about skipping SI's in a Safari (in Egypt, for that matter). Most divers don't take 100% O2 for those trips, and diving on a single mix, it is better to surface rather than tweaking SI's by doing extended stops.

 

[Charlie99]

Ignoring multigas dive planning for the moment, and going back to the original poster's question .......

Floater, why don't you just e-mail Martin Lorenzo, describe your upcoming trip and ask for his recommendations. Then post the response to enlighten us.

 

[Uncle Pug]

After reading TSandM's post along with input from UP and Doc Intrepid I get the gist of your deco plan..

Please don't misconstrue anything I've written as agreeing with or providing a basis for understanding Floater's *deco plan*. I haven't seen a *deco plan* in this thread.

What I have seen is Floater's stated reason for wanting to skip the SI:

I was planning on skipping the surface intervals when we go to some of the further away, better sites by boat. The ride can take 3-5 hours so once we are there I'd rather do 3-4 dives rather than the regular 2 that are included.

And the standard fundies NDL ascent:

30 sec stop at 70' .. with30 sec[ft/min] ascent followed by 30 sec stop each 10 ft

But most telling is this:

Since I'm still new to the system

Floater, this isn't the DIR system. On your vacation in the Philippines you were exposed to a remedial diving class that was intended to supply a foundation for possible future DIR training. You are taking it way beyond what was intended and for the wrong reason.

FWIW, I would rather do the 2 dives than 3-4 and enjoy the surface interval. BTW, going to sites "further away... by boat... ride can take 3-5 hours" is a great reason to keep your dives conservative.

First and foremost, a DIR diver is a safe diver!

 

[do it easy]

Getting back to the original tables that Floater posted, even with a SCR of .4, that dive would require about 400cf of gas. That doesn't include reserves, contigencies, etc. WIth a SCR of .6, it's almost 600cf of gas!!! How high do they pump tanks in Egypt?

Edit: Those might be run times in the original tables, in which case the gas requirements are more sensible, but I still wonder about the deco.

Edit: ohh forget it. I thought those were deco schedules- it's more like the rule of 120 table.

 

[*Floater*]

Getting back to the original tables that Floater posted, even with a SCR of .4, that dive would require about 400cf of gas. That doesn't include reserves, contigencies, etc. WIth a SCR of .6, it's almost 600cf of gas!!! How high do they pump tanks in Egypt?

Edit: Those might be run times in the original tables, in which case the gas requirements are more sensible, but I still wonder about the deco.

Edit: ohh forget it. I thought those were deco schedules- it's more like the rule of 120 table.

Each dive would take about 80cf. Since I plan to use doubles I'll have plenty in reserve. And I would change tanks between the dives.

These are "NDL" dives so there's no deco apart from minimum deco.

 

[*Floater*]

Floater, this isn't the DIR system. On your vacation in the Philippines you were exposed to a remedial diving class that was intended to supply a foundation for possible future DIR training. You are taking it way beyond what was intended and for the wrong reason.

So what minimum deco rules would you recommend?

 

[Uncle Pug]

Don't focus on minimum deco... focus on maximum safety.

I've detailed my approach in multiple threads here on SB, but don't have the links at my finger tips... and it is not appropriate for this forum anyway as it is not *DIR*.

What I can offer is this: Renting multiple non-DIR DM dive buddies to avoid doing the SI and stuffing in extra dives is not DIR.
If you go to the Red Sea and dive without a DIR buddy using a non-DIR operation just do the two dives they offer and include the normal SI.

I don't mean to sound rude or condescending with my posts... but I am seeing a serious safety issue here in what you have posted as well as a misunderstanding (or misapplication) of what you learned in your DIR fundamentals class.