MOD marking for 21/35

[limeyx]

The thing is Tech 1 doesn't take into account the use of a stage bottle, so the only 21/35 you would have would be a back gas, and back gas uses the 1.2ATA/100ft END. Stage bottle marking seems to be changing based on the use of the gas, ie bottom gas or deco gas. I did Tech 1 in Aug, and how it worked for us was 32% to 100ft, 30/30 80-120ft, 21/35 100-150, 18/45 150-200, 15/55 200-250, 10/70 250-300. Now obviously we weren't doing anything deeper than 170, but thats the gas table we were given. If I'm going to be diving something deeper than 140 I will use the 18/45 so that I have the extra buffer. I know people who don't mind pushing 21/35 to 160-165, but its not for me. If I think there is a chance of breaking 150 I'll dive 18/45. The marking of stage bottles seems to be fairly recent, and would only be covered in a Tech 2 I imagine, as thats where use of a stage bottle is taught. All the Tech 2 guys I dive with learned to use 190 for 21/35 and 240 for 18/45.

When I did T1 in 2006, I believe it was 1.2 PPO2 *average* on the bottom, so 21/35 was fine for a 160 dive with some time spent at 170 and equivalent time at say 140 to "make up for it"

Maybe 1.2 is the new max, but GUE are telling me that it has *always* been 1.2 max which I do not think was the way I understood it.

In practice, (for better or worse), plenty of people are using a bottom stage for T1 dives. I mark 21/35 as 190 for those dives because if I *have* to breathe it at 190 I will, and 1.4 is not likely to tox me even though it's stretching th depth for that gas quite a bit.

Some T2 people say dont even bother marking bottom stages for open water, just deco bottles -- they should be breathable at max depth, and if you go "below" max -- you have to breathe them anyway!

 

[limeyx]

From my Fundies course PPT taken June 2007 (copyright 2007 material)


Depth (Feet) -------------- Mixture (02/He)


Heh, so much for consistency -- we all have different numbers!

 

[lamont]

Some T2 people say dont even bother marking bottom stages for open water, just deco bottles -- they should be breathable at max depth, and if you go "below" max -- you have to breathe them anyway!

That makes a certain amount of sense to me. You don't put MOD stickers on backgas, and bottom stages are just backgas...

 

[KMD]

That makes a certain amount of sense to me. You don't put MOD stickers on backgas, and bottom stages are just backgas...

ummm no. Bottom stages are not backgas.... bottom stages are tanks that can conceivably be mixed up with your deco gas. Proper markings should be on them.

Gas switching procedure is there for a reason. One changes the procedures at their own peril. You can't visually confirm the MOD of a tank if has no sticker.

 

[rjack321]

When I did T1 in 2006, I believe it was 1.2 PPO2 *average* on the bottom, so 21/35 was fine for a 160 dive with some time spent at 170 and equivalent time at say 140 to "make up for it"

Maybe 1.2 is the new max, but GUE are telling me that it has *always* been 1.2 max which I do not think was the way I understood it.

EXACTLY it has gone from being average 1.2 to max 1.2 rather silently. Dropping the 100-120 usage of 30/30 and also eliminating 21/35 in the 150-190ft range (as backgas but not as deco gas) in the process. I would much rather have a clarifying memo on THIS issue than on freakin' pocket contents!

In practice, (for better or worse), plenty of people are using a bottom stage for T1 dives. I mark 21/35 as 190 for those dives because if I *have* to breathe it at 190 I will, and 1.4 is not likely to tox me even though it's stretching th depth for that gas quite a bit.

Yeah that's an uncomfortable stretch for me as backgas as well.

Some T2 people say dont even bother marking bottom stages for open water, just deco bottles -- they should be breathable at max depth, and if you go "below" max -- you have to breathe them anyway!

I could see this being the case when carrying one backgas stage, ya start out breathing it on the surface anyway (unless its 10/70 I guess). But what do they do when carrying 2? Do they only know they aren't switching to 50% at 200+ft because of the absence of a MOD label? That seems rather non-DIR.

 

[rainman_02]

So, the deepest you can dive with 100% is 20', the deepest you can dive with 50% is 70', the deepst you can dive with 35/25 is 120', and the deepest you can dive with 21/35 is 190'.

1.6, 1.6, 1.6, and 1.4 respectively.

Now, deco bottles and bottom stages do the exact same thing: extend bottom time. Sure, they do it in different ways, but that is their basic function. A bottom stage does this by increasing your available gas above rock bottom. A deco bottle does this by 1) reducing your rock bottom; 2) reducing your deco obligation through accelerated decompression. One is breathed at the start of the dive; one is breathed at the end of the dive. But that does not change their basic function: to extend bottom time.

So, if both are there to extend bottom time, why should we have two standards for marking the bottles? Isn't part of the "philosophy" of the system to be modular (i.e. -- you dive each dive the same way but only add the gear you need based on the requirements of the dive)? And if that is the case...

Here's about the best example I can think of:

On day one of a trip I go for a deep dive requiring the 190 bottle for deco. So, I dive with a bottle marked 190.

On day two, I go for a 150' dive with a bottom stage (for example a long shallow scoot out to a deeper site where I still want my "max" bottom time). I dive with a bottle marked 190.

Otherwise I have to re-label my 190 bottle...or have a 190 bottle and a 150 bottle. Why?



KISS. 20, 70, 120, 190. Every bottle gets marked.

 

[nadwidny]

I could see this being the case when carrying one backgas stage, ya start out breathing it on the surface anyway (unless its 10/70 I guess).

Even when I'm on 10/70 I start it at the surface. Put reg in face, don't screw around and hit 15-ish feet. Boom, breathable gas.

But what do they do when carrying 2? Do they only know they aren't switching to 50% at 200+ft because of the absence of a MOD label? That seems rather non-DIR.

Think about it. In the extreme likelihood that you are carrying 2 stages of bottom gas, both of those are clipped up top. Deco gas is leashed. When you are switching from one stage to another there are no deco gas cylinders to get confused with.

Frankly I can't think of any OW dive that I've done that would require 2 stages. But then again I usually dive with George's philosophy of more shorter dives rather than one long one.

FWIW I only have marks on my deco cylinders and don't have any marks on my stages. Come to think of it, when I did Cave 2 we didn't have marks on those stages either.

 

[rjack321]

I don't necessarily disagree with you, although you're not 100% correct. Supposedly the deepest you can dive 21/35 as backgas is (now) 150ft, ppO2 of 1.2 (rounded up a tad) not 1.4

Just as, if not more, confusing if I bring a stage of 32% its marked exactly the same as a stage of 30/30. Or is the guideline to mark 30/30 "120" but only use it to 100??

I was cool with the max 1.4 but try to average 1.2 that I was taught. In light of recent fatalities I am aiming for more max 1.3. But it seems that current standards have slowly shifted to max 1.2 and to mark bottles for that max.

 

[rjack321]

Think about it. In the extreme likelihood that you are carrying 2 stages of bottom gas, both of those are clipped up top. Deco gas is leashed. When you are switching from one stage to another there are no deco gas cylinders to get confused with.

Frankly I can't think of any OW dive that I've done that would require 2 stages. But then again I usually dive with George's philosophy of more shorter dives rather than one long one.

FWIW I only have marks on my deco cylinders and don't have any marks on my stages. Come to think of it, when I did Cave 2 we didn't have marks on those stages either.

I watched video of AG's dive at "The Crack" the other day and all of their bottom stages were marked (5!). I hear what you're sayin' though. For my purposes I agree that labeling a bottom stage isn't required. Its almost always taken to get 2 dives off 1 set of doubles.

The real question is why is there such variation in "DIR" about MOD labelling

 

[nadwidny]

The real question is why is there such variation in "DIR" about MOD labelling

Because we are thinking divers and not mindless koolaid drinkers.