Quick Question about O2 bottle

[Nick Ambrose]

Again, your question needs to be addressed to Ross. I did not change any settings between those 2 profiles. The only difference is the descent to 250'.

I dont need to go ask Ross anything, I understand how the profiles I am diving are made. Seems maybe you should be the one asking Ross to explain the profile if you don't really understand it.

[Nick Ambrose]

So, why is there such a difference between OW and cave deco? I know quite a few cave divers that have gotten bent getting out of the water 15-20 minutes before I would. But yet, it seems that would be okay in OW.

I think there are a few possibilities

1) Maybe it's not (just) the time of deco but also the shape that matters (and gas selection)
2) It's easier to stash O2 in a cave than carry it on the entire dive, so less of a penalty for bringing a bigger bottle
3) Most of the cave diving we (I?) hear about is in relatively warmer waters so the cost of extra deco time (assuming no emergencies) is relatively less
4) Cave dives tend (again somewhat generalizing) relatively longer BT and relatively shallower than OW tech dives. I think (and I am no expert) but I think there is maybe less known about this kind of deco relative to shorter bottom times mostly since the vast majority of people aren't doing those kind of dives.
5) Profile of the cave definitely comes into it in some cases I am sure, as we did a dive admittedly in OW but following a line along the bottom where even with scooters it was somewhat a challenge to meet the exact schedule we wanted.
6) I am wondering also if it's anything to do with the fact that probably more OW tech dives are done with Helium mixes, as compared to a lot of Florida caves that are done on Nitrox --- maybe something to think about

[LCF]

I wonder if it has to do with temperature, too . . . I had some fascinating conversation with some hyperbaric research types last night about temperature and decompression, where they told me about some hot water experiments that showed that, if you were warm through your bottom time, even if you stayed warm through decompression, you actually needed significantly more deco. Most of the cave diving I'm familiar with is in relatively warm water. I wonder if people doing deep dives in tropical ocean water have found some need to adjust deco schedules?

[jj1987]

I'd guess a lot of the DCS hits in NFL come from

1) Trying to do back to back to back extremely long decompression dives each weekend.
2) Staying up late or waking up early to get as many dives in per day as you can, or travel between sites.
3) Dehydration. Another downside to the GOGOGOGOGO that many do. Very few water fountains around cave country, lots of ice boxes on dive boats.

8 cave divers got bent in a single month last year. I talked to several, and many of them were on repetitive dives and dehydrated. I've noticed that I have a lot more time to kill (ie time to hydrate), and dive only twice a day (shorter dives at that) on a boat.

Clearly rock overhead doesn't change things. Maybe it's the ups and downs, but since Ginnie seems to be the #1 "bender cave", I don't think that's it. I think time is better spent on behavioral differences rather than the dive site it's self.

[Dive-aholic]

I dont need to go ask Ross anything, I understand how the profiles I am diving are made. Seems maybe you should be the one asking Ross to explain the profile if you don't really understand it.

I do understand the profiles I'm doing. I also understand I've never seen the inside of a chamber because I have to. While you're doing direct descents to 250', I'm spending time at various depths before I get there. At those depths I'm getting a constant nitrogen upload. The descent times aren't much different. What's different is the shape of the descent. So, your first possibility listed in post #62 is the reason the obligations are different. The rest of your list has nothing to do with it.

2) It's easier to stash O2 in a cave than carry it on the entire dive, so less of a penalty for bringing a bigger bottle
3) Most of the cave diving we (I?) hear about is in relatively warmer waters so the cost of extra deco time (assuming no emergencies) is relatively less
4) Cave dives tend (again somewhat generalizing) relatively longer BT and relatively shallower than OW tech dives. I think (and I am no expert) but I think there is maybe less known about this kind of deco relative to shorter bottom times mostly since the vast majority of people aren't doing those kind of dives.
5) Profile of the cave definitely comes into it in some cases I am sure, as we did a dive admittedly in OW but following a line along the bottom where even with scooters it was somewhat a challenge to meet the exact schedule we wanted.
6) I am wondering also if it's anything to do with the fact that probably more OW tech dives are done with Helium mixes, as compared to a lot of Florida caves that are done on Nitrox --- maybe something to think about

2. There's no penalty based on bottle size.
3. There's no temperature factor in any of the decompression programs I've seen. And there's no programming in there that lets it "figure it out".
4. You put in the same bottom time in V-Planner, or Deco Planner, or GAP, or whatever other program and it's still different. I'm comparing 2 dives to the same depth, just with a different descent. It has nothing to do with bottom times or shallower depths. I can get to 350' in a few caves in Florida with no problem.
5. If it's a cave I don't know I plan maximum depth regardless of the exact depth profile. If it's a cave I'm familiar with, I may plan based on an average depth. Yes, I know that's not acceptable in OW diving, but it's necessary in some caves so the decompression obligation isn't outrageous.
6. I'm not comparing trimix vs nitrox. I'm comparing 2 hypoxic mix dives.

I wonder if it has to do with temperature, too

There's nowhere in any program I'm familiar with for a temperature gradient. Profiles are based on depth and time.

I'd guess a lot of the DCS hits in NFL come from

1) Trying to do back to back to back extremely long decompression dives each weekend.
2) Staying up late or waking up early to get as many dives in per day as you can, or travel between sites.
3) Dehydration. Another downside to the GOGOGOGOGO that many do. Very few water fountains around cave country, lots of ice boxes on dive boats.

8 cave divers got bent in a single month last year. I talked to several, and many of them were on repetitive dives and dehydrated. I've noticed that I have a lot more time to kill (ie time to hydrate), and dive only twice a day (shorter dives at that) on a boat.

Maybe for the people you know that's the case. But the specific incidents I'm thinking of were not based on this. In fact, I'd venture to say that most cave divers doing hypoxic dives are keeping to one dive a day, whereas someone paying $3000 to do a 3 day Doria trip will be doing 2-3 hypoxic dives a day while out there.

[Nick Ambrose]

I do understand the profiles I'm doing. I also understand I've never seen the inside of a chamber because I have to. While you're doing direct descents to 250', I'm spending time at various depths before I get there. At those depths I'm getting a constant nitrogen upload. The descent times aren't much different. What's different is the shape of the descent. So, your first possibility listed in post #62 is the reason the obligations are different. The rest of your list has nothing to do with it.

I'm going to bow out of the "discussion" at this point. It's pretty obvious we plan and execute our dives in radically different ways.
We also seem to be talking at "cross purposes" in many posts so there really isnt much point in continuing.

Safe Diving.