OC Gas switch protocols?

[PfcAJ]

What I'm saying is, your protocol for air breaks is they are done at switches AND they are done at intervals. So, you're mixing your air break protocol into your gas switch protocol, instead of keeping them separate. And you have mixed criteria for doing air breaks.

Why not make them completely separate and simple? Gas switch protocol is "this" and has nothing to do with air breaks. And air breaks are based on "this" (intervals) and are handled separately from gas switches.

That seems like it would really simplify gas switches. And you could still do just as many air breaks as you want. I don't know. I guess if you feel like always doing at least a brief air break every time you do a gas switch is beneficial, then just building it into the gas switch protocol makes sense. But, it sure does seem like a lot of people are doing "basic" dives in the 240 or less range without doing those extra air breaks and they're getting out okay. At least enough that a lot of agencies teach it that way.

Is there any agency that specifically teaches Method 1 (back gas between deco gases)?



What does that mean? You usually add a 3rd deco gas when you plan for deeper than 170'?

Going to backgas between deco gases serves two functions:

1- gas break before switching to a high ppo2 gas to prevent oxygen toxicity.

2- gives you something to breath while you're putting away the hose for your deco bottle and preparing the hose for the one you're switching to.

Gas breaks during the oxygen stop are to prevent oxygen toxicity.

That's it and that's all. Simple. How could it get more simple?

The duration of the backgas break before the switch is usually the length of the stop or (if the stop is REALLY long) some fraction of it. I try and use 50% of the length of the stop.

GUE teaches backgas between deco gases. Consistency of switch procedures and only one deco bottle on and deployed at a time are big benefits to switching to backgas between deco bottles.

You asked me when I add a 2nd deco bottle and when I add a 3rd.

2nd deco bottle comes into play around 170'. 3rd deeper than 200' on a cave dive or something past 240' (maybe even 270') in the ocean. Lots of variables in the ocean compared to caves and that complicates the question.

 

[CptTightPants21]

Switching to back gas is more about keeping your neck from becoming cluttered with reg hoses and simplifying the switch, the O2 tox argument is more of an "added benefit".

 

[tbone1004]

Right. So, first, I'm not really asking about cave scenarios because I know just enough about cave diving to know that gas planning for that is a whole different ball game than gas planning for deep wreck diving. I suppose I should have said up front that I'm talking about OC and OW. But, I didn't because I didn't really expect gas switch protocols to be any different between the two.

So, assuming OC and OW, at what depth do you start at least thinking about carrying 3 deco gases? I think 150' is about where I would be looking at carrying 2. So, where for 3?

The protocols are already different because we stage our deco bottles in a cave so things get dropped off and picked up in sequence. I have 0 risk of switching to O2 at 70ft on an OC cave dive, because my O2 is at 20 ft at the entrance of the cave. Simultaneously, because I have to go somewhere to get to said bottle, when I'm done with my stop, I have time to kick around while stowing the bottle, so the profiles get rather wonky in comparison because our ascent has a lot shallower profile than an OW ascent because of that linear penetration that is typically required.

In OW it all depends on the depth/bottom time combo and ascent profile on top of the surface conditions. You have to run the numbers and see when it makes sense to add that extra piece of equipment and how much deco time it is really saving you

 

[PfcAJ]

The protocols are already different because we stage our deco bottles in a cave so things get dropped off and picked up in sequence. I have 0 risk of switching to O2 at 70ft on an OC cave dive, because my O2 is at 20 ft at the entrance of the cave.

Be careful with that line of thinking. That's what lead to Jim Miller's death.

 

[tbone1004]

Be careful with that line of thinking. That's what lead to Jim Miller's death.

of course, we still do proper gas switching protocols when we pick it up, to make sure we didn't drop the bottles in the wrong order, but that was really to exaggerate the differences since we can stage our deco bottles

 

[C Dub]

Stuart you should just take fundies then however much of the GUE Tech line floats your boat. Every procedure is done for very clear and defensible reasons. Exactly what a highly analytical person like you needs.

 

[stuartv]

Stuart you should just take fundies then however much of the GUE Tech line floats your boat. Every procedure is done for very clear and defensible reasons. Exactly what a highly analytical person like you needs.

I really want to do that. I was hoping to do it this year (Fundies). But, I just had an unexpected opportunity fall in my lap to begin TDI Divemaster training with the tech instructor I did my AN/DP and Helitrox with. I couldn't pass that up. He told me he hopes to get me through by the end of the year, but it could be this time next year. So, I don't see any way I will fit Fundies into my schedule now, until at least sometime next year. And TDI Trimix is currently a higher priority for me (than Fundies), so.... we'll see.

 

[boulderjohn]

Be careful with that line of thinking. That's what lead to Jim Miller's death.

For those who don't know, Jim Miller died in a cave after two failures of gas switching protocols. In the first failure, the team dropped their 70 foot deco gas bottles at 70 feet, but Jim somehow dropped his bottom gas there instead. In the second failure, Jim intended to switch to that bottom gas at 120 feet, but he switched instead to the 70 foot bottle he was supposed to have left behind earlier. He then continued to 240 feet, and he was there for quite a while before he toxed.

This event was in my mind when I made the earlier post about gas switch protocols. The organization with which he trained has the most elaborate and (in theory) safest gas switch protocols I know. When it happened, the cave diving world's reaction was a collective "How on earth....?" I, of course, was not there, and so I did not see what actually happened. I had never met Jim or any of his buddies, let alone dived with them, so I cannot make any statements about how these two mistakes were made. I only know what I said earlier. I was trained originally to use those same protocols, and in my experience, those protocols tend to be ignored by experienced divers outside of training because they are very time consuming. They would especially tend to be ignored on descent (when both errors occurred), because you are usually in something of a hurry and do not have the luxury of hanging around at that depth long enough to follow elaborate procedures and take a good look at each other's gear to make sure the switches were made properly.

 

[PfcAJ]

I'd argue that you do have time on descent, but it takes discipline to use that time.

A few seconds/minutes to make sure everything is in order is time well spent IMO.

 

[stuartv]

@boulderjohn What agency did you train with that had the most elaborate gas switch protocols?