100m dive

[rjack321]

If you go back to the originally question though when people were asking about "why not 80%," if you don't believe in carrying 100% with single bottle deco and are okay with 50%, where do you draw the line? Why not 80%? Why not 40%? Why not 60%? You can make any of those work with single bottle.

Decompression theory wise, there is a theoretical benefit to decoing at 1.6 pp02/essentially doing your entire last stops on 100% at 20ft rather than going 20 then 10. If won't change the time on your computer, but efficiency wise it's better (if you believe in the oxygen window) and theoretically would be safer in terms of chance of DCS hit (see Mark Powell Deco for Divers). You can't do that if you don't carry 100% O2

For a single bottle dive you are looking at roughly a 45-50m max depth, assuming a realistic BT in the 15-30min range. Why not longer? You cant do the deco on BG longer.

So in that exposure range where is you first stop? Its not at 100ft so why switch there (40%)? As AJ said its a good long time to get up to 20ft which makes the 100% option not good from a min-gas angle. What does that leave? 80% and 50% or perhaps 60%.
100% - great for deco, min gas too big
80% - shorter time to get there (vs O2) but min gas is still high
60% - would work well, except once you add O2 as a second deco gas (for other dives) you are not on the 60% for long for very long and the stop to get to a 55ft switch depth are no significant. I.e if you do a 200ft dive for 25mins you have min gas issues getting up to 60% and then not very much time on the 60% before switching to 100% so its a less than versatile gas choice
50% - minimizes min gas issues. works across the range of decos for a single deco gas and once you add O2 for more substantive exposures it still works.
40% - 1st stop far deeper than you'll ever realistically have for a single deco gas dive, not a good switch depth
32% - not enough O2, way too much N2, first stop way too deep

Have roughly 5 stops per deco gas (O2 being an exception) seems to work out both from a stop depth and a "how long am I on this gas" perspective. Hence the 100m suggestion to use 21/35, 35/25, 50%, and O2 for deco on a 100m dive.

 

[nadwidny]

If you go back to the originally question though when people were asking about "why not 80%," if you don't believe in carrying 100% with single bottle deco and are okay with 50%, where do you draw the line? Why not 80%? Why not 40%? Why not 60%? You can make any of those work with single bottle.

One George Irvines's arguments for 100% vs anything else was that sometime things go seriously sideways and first aid for DCI is 100%. Not 80%, 60%, or anything else and if you need it then it's better to have it on you.

 

[Trace Malinowski]

Thanks @Trace Malinowski. It's important to recognize that people who are experiencing cardiac problems experience some important changes in their physiology relative to healthy individuals. So examining the role of oxygen administration in sick versus healthy patients might not tell us very much. With that said, the short-term toxic effects of free radical production/oxidation that occur with the metabolism of oxygen are fairly well known. Our mitochondria have evolved to help control the damaging effects of oxidation during metabolism. But, they evolved to deal with this in a 1 bar world. So perhaps we shouldn't be surprised if we later discover longer-term negative effects of high oxygen exposures. I work with a respiratory therapist and I was telling him about the kind of oxygen exposures that tech divers are often exposed to; he was pretty shocked.

Yes. I thought it was interesting that 100% O2 wasn't as clear-cut right across the board as being medically perfect. People seem to jump on the latest and greatest trends such as yoga or superfoods. Scientists still can't tell us if eggs and milk are good for us or bad for us. I love milk so I'm drinking it anyway. Eggs I can take them or leave them. When diving, I don't really care what gas I'm using. I did the air thing. I did the nitrox thing. I did the DIR thing. People are now telling me I shouldn't do the DIR thing because of deep stops. Dive plans I've used have set every caution color off in V-Planner. I believe too much equipment and too many gas choices are worse than keeping things simple. Plan practically rather than theoretically. The DIR approach tends to keep it simple for me.

 

[Superlyte27]

Trace:

People talk to me about my gas planning and stops too. The funny part is, I’ve been diving longer than most of them. Have done bigger dives then a lot of them, and have never been bent. And every single one of them have been bent. I tell them, when I’m ready to give up my perfect record in 10k+ dives of bend free, I’ll start diving their way.

Edit*
For the record, 100% O2 and last stop at 20’

 

[Trace Malinowski]

Pete, how much do you charge to plan dives?

 

[Superlyte27]

Pete, how much do you charge to plan dives?

For you? Nothing. LOL

 

[Billy Northrup]

Good stuff, always.

I'm more interested in your work up dives to this point. How has your planning been surviving real world contact? Example not just consumption rate "but hey I reel allot slower than I thought off that first switch" and how that plugs back into lost gas scenario? That rebreather team jams the line 6 and 3 meters so it takes me forever to get to my 100% when I could be chilling at 80%.

One if my hot drop dives (heavy work) puts me on the rail at 205 feet, so I sit on my 21/35 travel and calm down my breathing, dump CO2 and a good way point to switch to my BG. Can any terrain features infl
uence your choices?

You need to gather your data on your site and plug it back into your plan. Saying hey I'm going 100 meters without working it up kinda freaks me out a bit.

FWIW I dive with a team that uses 80% for the final gas, that's fine by me. However I tuck my lil 30cf of 100% under my arm, I don't activate it in my computer and it's not part of my gas plan. It's a peace of mind, I'll use it for sure when I can.

 

[Superlyte27]

Good stuff, always.

I'm more interested in your work up dives to this point. How has your planning been surviving real world contact? Example not just consumption rate "but hey I reel allot slower than I thought off that first switch" and how that plugs back into lost gas scenario? That rebreather team jams the line 6 and 3 meters so it takes me forever to get to my 100% when I could be chilling at 80%.

One if my hot drop dives (heavy work) puts me on the rail at 205 feet, so I sit on my 21/35 travel and calm down my breathing, dump CO2 and a good way point to switch to my BG. Can any terrain features infl
uence your choices?

You need to gather your data on your site and plug it back into your plan. Saying hey I'm going 100 meters without working it up kinda freaks me out a bit.

FWIW I dive with a team that uses 80% for the final gas, that's fine by me. However I tuck my lil 30cf of 100% under my arm, I don't activate it in my computer and it's not part of my gas plan. It's a peace of mind, I'll use it for sure when I can.

Those are the issues aren’t they.
When teaching a trimix class, we cut tables. That could come from anywhere you want, IDECOPRO, Shearwater, Vplanner, actual tables, whatever. Those are printed and kept in wet notes or pocket, whatever. But if the dive says your bottom time is 25 minutes, you better be leaving the bottom AT 25 MINUTES. If it says you’ll reach your first stop at 28 minutes, then you HAVE to be on the numbers. If you miss anything, your tables are junk. So, when learning Trimix, if you miss leaving your BT at the proper time or miss reaching your first stop, or even miss any of your subsequent stops, you’ve failed that dive.

Yes, I realize GUE does it differently.

 

[boulderjohn]

o, when learning Trimix, if you miss leaving your BT at the proper time or miss reaching your first stop, or even miss any of your subsequent stops, you’ve failed that dive.

If you are doing your dives by cutting written tables, then you should have some written contingency plans as backups to your primary plan.

 

[Superlyte27]

If you are doing your dives by cutting written tables, then you should have some written contingency plans as backups to your primary plan.

We do. But the purpose of the class is to test one’s abilities following directions the first time, not the plan b. Lol
Pretty sure you learned from the same guy I learned from.