Standard MOD

[liuk3]

Nick, the way GUE teaches the labeling is to have distinct standard markings for deco and stage mixes of varying depths. PfcAJ listed them in a post above. You can tell which gas mix is in them and whether it is a deco gas or a stage gas depending on the standard MOD marking protocol on them.

 

[Jarrod]

Thanks Nick. I am happy to participate. I think your community is handling this very sensibly by evaluating various positions, trying on different perspectives and assembling an opinion. I am sorry if it appeared I was discouraging discussion. The exchange of information is almost always useful.

GUE's bottle markings create distinct depths for deco and bottom gasses so this confusion shouldn't occur. For example, there is no 120 bottom gas; this is a deco gas marking and it tells me this is 35%. The 150 MOD tells me it is a bottom gas. These gases were not created with an obsessive eye toward PO2 or END but were crafted to be easy to use and remember. Small variations in PO2/END are not important if you have a reasonable margin built into your planning/gas strategy. By the time a diver grasps the range of nuances covered by most of you in these discussions then they are knowledgeable enough to use common sense in making needed adjustments. If it doesn't make sense or they are unclear about these parameters then sticking to the hard line is easy and appropriately conservative. I hope you all have a great weekend.
Best,
Jarrod

 

[limeyx]

Thanks Nick. I am happy to participate. I think your community is handling this very sensibly by evaluating various positions, trying on different perspectives and assembling an opinion. I am sorry if it appeared I was discouraging discussion. The exchange of information is almost always useful.


Jarrod

Jarrod, it didn't come across that way at all. I think perhaps "discussion" is not something this thread needs too too much else of

Is it then correct, that the official GUE MOD's are (as Ken pointed out were already posted)


Deco:
20, 70, 120(35/25), 190(21/35) 240?(18/45?)

Bottom:
100, 150(21/35), 200(18/45), 250(15/55?), 300(10/70)

with 12/65 slotting in as a new bottom mix ?

I ask this, as I dont have GUE tech2, but do dive with some divers that have taken that training, and want to make sure we are on the same page.

I believe I have seen some 220 MOD's used by GUE divers here and I don't see that on the list for instance....

EDIT: Apologies, I had a mistake in the deco gas list...

 

[rjack321]

GUE's bottle markings create distinct depths for deco and bottom gasses so this confusion shouldn't occur. For example, there is no 120 bottom gas; this is a deco gas marking and it tells me this is 35%. The 150 MOD tells me it is a bottom gas. These gases were not created with an obsessive eye toward PO2 or END but were crafted to be easy to use and remember. Small variations in PO2/END are not important if you have a reasonable margin built into your planning/gas strategy. By the time a diver grasps the range of nuances covered by most of you in these discussions then they are knowledgeable enough to use common sense in making needed adjustments. If it doesn't make sense or they are unclear about these parameters then sticking to the hard line is easy and appropriately conservative. I hope you all have a great weekend.

Personally I am fine if there isn't a 1:1 relationship between a MOD and a gas. In fact if it keeps divers on their toes a little bit about analyzing every cylinder that's a good thing

I still mark 30/30 as "120" for instance and many GUE divers I know are happy to dip below 100ft on this gas. Not for hours and hours but in a 30min wreck penetration averaging a ppO2 of 1.2 its not really an issue. Yes "120" is also 35/25 but I don't have that many stages and our plans aren't that convoluted where this kind of mix-up is really plausible even if proper analysis were for some dumb reason omitted.

As long as people are actually marking all their bottles and the MODs pass some sort of bottom ppO2 laugh test (1.2 - 1.4) I'm happy.

 

[Jarrod]

Thanks Nick<g>. You have it correct. 12/70 was meant to replace 10/70 and we would adjust O2 with deeper/longer dives in what is essentially a Heliox mix. Deep or long dives require more tinkering sometimes but by then someone should be pretty comfortable in this arena.

RJack, I am sure you are quite capable of these adjustments though I would personally rather mark 110 so as to avoid confusion with deco gases.

Best,
Jarrod

 

[Jarrod]

Hey Gang, I hate to beat a dead horse but a discussion on the GUE forum left me feeling I had not properly outlined my thoughts on the whole PO2/MOD issues. I have seen this question a few times and I feel a strong focus on PO2 obscures our intent in creating standard gases with fixed MOD marking. I apologize for the double posting but I think this is an important issue.

The way we conceived the standard gas/MOD system bottles should be marked according to the MOD for the particular standard gas. There is no reason to change the MOD for a particular gas. The mechanisms associated with toxicity are just not that precise and corrupting the system is far more dangerous than the .1 difference we are talking about here. Of course if one is diving near the limit and prefers more conservatism as compared to what is offered by the standard GUE gases then we just use the next deeper gas. There is no value to marking bottles according to a specific, hard line on PO2 (ie 1.4). This would result in all sorts of varying depth markings for MOD stickers and corrupt a lot of the value in the standard system. Knowing what is in a tank based upon the listed MOD is very useful to all divers in the water.

Because none of these mechanisms are particularly precise it is useless to argue that a hard line of 1.4 (or any other PO2 for that matter) is the absolute MAXIMUM. It is reasonable, useful and recommended for one to calculate the PO2 variations with deeper drops on a particular gas but these should not be used to create a new labeling strategy for a standard gas. If we re-marked our bottle to 1.4PO2 would that really be the absolute limit should an out of gas buddy require assistance? Very short exposures to high PO2 are extremely unlikely to create a problem ( as evidenced by the 1.6 exposures we maintain all the time). The reason to dive around 1.2 is to reduce O2 accumulation at depth and provide a significant buffer should an emergency require. One need only do some quick math to see a linear progression regarding PO2 increase with deeper depth. Let's assume roughly .1 per 20' for rough math. If we start at 1.3 for bottom mixes and add .1 at each 20’ we can see 1.3 @ 200, 1.4 @ 220, 1. 5 @ 240. A simple review like this allows me to maintain all the value to standard gas marking, quickly show everyone what is in my bottle (because of consistency with MOD stickers) and quickly assess how much risk I might take given the particulars of a situation.

To be honest picking a cutoff depth during an emergency is always going to be extremely arbitrary. If you are diving GUE standard mixes as they are intended you have a nice margin which keeps you insulated from excessive O2 accumulation at depth while leaving ample wiggle room for emergencies or even adjustment by advanced users. The intent has always been to create thinking divers supported by well developed procedures. The value to these standards is mostly related to having a standard and secondarily as pertains to the detail of the standard. This is not to say the details are unimportant but to emphasize that we can’t lose the forest for the trees. Obsessing about a tenth of a PO2 within a system already providing ample conservatism merely confuses the issue and exposes us to much greater risks. This is why I said the whole non marking of bottom stages reminded me of when we used to have to argue about Nitrox banners. We can’t lose sight of the real risk in a given situation or we let superficial issues confuse our sense of risk and encourage contamination of long standing and successful strategies.

Ok, sorry gang. Happy to let this one alone now

All my best,
Jarrod

 

[Blackwood]

If we re-marked our bottle to 1.4PO2 would that really be the absolute limit should an out of gas buddy require assistance?

I certainly hope not.

A reply I made in a similar thread on dive matrix:

Personally, I treat it in the same way I treat backgas. If I need to violate the MOD, so be it. I'm not going to reference the bottle makings in making that decision. Same story for deco gas. If we're decoing on 50% and you have some issue that necessitates me descending below MOD, the 70 sticker on my bottle won't come into play since I already know what I'm breathing.

I elect to mark all my bottles for consistency and for future compatibility (e.g. easily differentiating between travel gas, bottom gas, etc.) even though I have no specific plans to go through hypoxic trimix.

At the end of the day, knowing what I'm breathing and knowing what my team is breathing is of paramount concern. I like the MOD marking as an indicator allowing my buddy to verify my gas switch, and for me to verify his. The standardized approach simplifies things and opens up more brain bandwidth for making decisions such as "am I going to go deeper and, if so, how much?"