Rule of 120 question

[Big-t-2538]

MikeFerrara once bubbled...


I thought RavenC already do a DIRF?

Nope...that was SeaJay

 

[MikeFerrara]

Charlie99 once bubbled...

To use a term you are undoubtably familiar with: "STROKE ALERT!". 45 minutes at 100' is quite a ways beyond NDL, even with EAN32

Great but now leave 100 ft with enough gas to get you and your buddy to the surface doing a nice diver freindly ascent and then where are you?

Any one planning a 45 minute dive to 100 ft on a single 80 needs more than the 120 rule or even a computer to help em.

 

[Charlie99]

MikeFerrara once bubbled...
Great but now leave 100 ft with enough gas to get you and your buddy to the surface doing a nice diver freindly ascent and then where are you?

Any one planning a 45 minute dive to 100 ft on a single 80 needs more than the 120 rule or even a computer to help em.

I didn't say that I'd do that dive. I was just questioning Braunbehrens statement that "using nitrox 32 you are pretty much guaranteed to run out of gas before ndl."

Let's review some numbers. I use an NDL of 30 minutes at 100' on EAN32. 100' is 4ata. 4*30=120 equiv. surface minutes. At the low, but not unusual for warm water drift, SAC of 0.33, thats only 40 cubic feet. If you are at 110', still within 1.4ppO2, even at 0.5cu ft /min you will easily exceed NDL.

My point is that you can't just say "I'm on nitrox, so I don't have to worry about NDL".

I'll do another reply and start a thread on "rock bottom".

 

[Spectre]

Charlie99 once bubbled...
I didn't say that I'd do that dive. I was just questioning Braunbehrens statement that "using nitrox 32 you are pretty much guaranteed to run out of gas before ndl."

I took a double take at that comment as well. However I believe he was responding [agreeing with] your comment of: "Then remember 50', 80 minutes. You'll probably be out of gas before hitting NDL for anything shallower. ". E.g. gas before ndl @ 50 or less.

 

[Braunbehrens]

Notice I said "pretty much". You always have to be careful on square profiles. Plus if you go that deep you'll be doing more stops on the way up. Your numbers are also a bit extreme, your NDL a bit low, and there is no accounting for rock bottom.

Still, you are right that you can't rely on the tank to set your limit for you. I dive doubles on every dive anyway, but I should have been clearer.

Having said that, I wonder how it would have been received on this board if *I* had called *you* a stroke, instead of the other way around.

This kind of anti DIR double standard really ticks me off. Next you'll be saying how rude we DIR divers always area.

 

[Charlie99]

Braunbehrens once bubbled...
Having said that, I wonder how it would have been received on this board if *I* had called *you* a stroke, instead of the other way around.

This kind of anti DIR double standard really ticks me off. Next you'll be saying how rude we DIR divers always area.

Sorry. I didn't mean to offend you. Even without having met you, it is clear from your posts that you can read an NDL table and calculate gas requirements.

Attempts at humor are dangerous on the Internet.

At least you didn't express offense at me misappropriating the DIRF acronym.

Charlie

 

[Charlie99]

Braunbehrens once bubbled...
Notice I said "pretty much". You always have to be careful on square profiles. Plus if you go that deep you'll be doing more stops on the way up. Your numbers are also a bit extreme, your NDL a bit low, and there is no accounting for rock bottom.

Some dive sites tend to have square profiles -- such as wrecks.

Another good example are the "third reef" off of the SE coast of Florida, 40 miles north of Miami. 85-90' on the outer edge, with only about 10' of wall or relief. So diving that will pretty much be at a constant depth. The inner edge is similar, but 65' or 70'. Usually a nice current, so you don't have to fin.

Part of my sensitivity to your comment is that while diving those reefs, NDL is generally my limit, even with an AL80, fairly hot mixes (34% and 37%), and leaving the bottom with reasonable reserves. This is one of the few places I've been where it is an issue -- mostly because some of the local divers have good SACs, dive with HP100s, and use SIs less than an hour.