Planned deco on a recreational dive?

[Patoux01]

Okay, bad understanding, seems better now.

I still disagree with it however, as has been said, 2 computers will give different runtimes, with none of them being known for being more dangerous than another.


Disclaimer: I'm a dangerous, mad, insane, crazy diver that gives his life no value, dives by himself, etc etc.

As far as doing this dive, I'd probably have done it, but I'm superman . You don't need to have a card to know what you're doing (and you can have a card and still be clueless), so my answer to OP would have been:
- If you're not sure you know what you're doing, don't do it.
- If you have true redundancy in your equipment and knowledge of the various procedures you might need, then you don't need our advice.

Then there's factors like "what is there to do?", "what are the conditions?" etc. (which have probably been answered, but I didn't read the whole thing yet ) which would decide if you do it or not, but these are true for basically any dive.

 

[barth]

Wow another instructor who thinks that the loss of gas at a deco stop is worse than loss of gas on the bottom during a recreational, unplanned deco dive which is conducted without a redundant gas supply.

Have you ever done a CESA with zero air from 100 or 125 feet? Just curious if you have actual experience in something similar.

For me it doesn't matter when all the gas is lost. If one diver is loosing his gas we thumb the dive and do the stops, The other team member(s) should have enough for all the stops of the complete team, it doesn't matter if that is a 60 feet rec dive or a tech dive.

I haven't tried cesa for ten years. I don't understand when I need it.

 

[irsubmarine]

Sorry for not posting earlier, I had to wait for my deco stop to end before I could respond...

3. What is your gas management for the dive?

The shop seems to use the rule of thirds. The divers were known to the shop so they seemed to know each others skill level quite well.

Yeah . . .MGR/Rock Bottom would be 63 cuft; round it up conservatively to 70 cuft/1980 liters. Assuming stressed breathing volume SAC rate of 1cuft per min/30liters per min for each diver, that would cover two divers sharing Air from 150'/45m, with 30 second deco stops/30 second ascending movements every 10'/3m to the surface starting at 70'/21m.

@irsubmarine said they were going to use single 15L/230 bar(?) cylinders (117 to 120cuft @3442psi). Let's use 117 cuft (Faber steel hp117): So 117 cuft minus 70 cuft MGR equals 47 cuft of Air usable. Assuming 0.6 cuft/min nominal SAC, they would consume 33 cuft of Air out of 47 cuft usable at 150' (5.5ATA) in 10 minutes maximum bottom time. SPG reading of @2100psi (MGR) ends the dive or max elapsed bottom time of 10min -whichever occurs first- to start a nominal 30fpm ascent rate to the deco stops. Last stop at 20' for either 6 minutes or a slow 3fpm ascent to surface.

In Metric:
3450 liters minus 1980 liters equals 1470 liters of Air usable. Assuming 17 liters/min nominal SAC, they would consume 935 liters of Air out of 1470 liters usable at 45m (5.5ATA) in 10 minutes maximum bottom time. SPG reading of @140bar ends the dive or max elapsed bottom time of 10min -whichever occurs first- to start a nominal 10mpm ascent rate to deco stops. Last stop at 6m for either 6 minutes or a slow 1mpm ascent to surface.


Go talk with the Divemaster and see if the plan was something similar to the above.

Then go get Advanced Nitrox/Decompression Procedures trained and use the correct deco gases next time, either Nitrox50 or 100% Oxygen, to give you a better margin against inert N2 tissue supersaturation & potential pathological bubble formation (DCS) upon surfacing.

SAC, cuft, I need to look up those terms. I think that presents the problem right? I.e. I definitely need training. Planning do go TDI once I hit 250 dives.

That is the point: with some more training the dive can be done safely.

Alas, the DM in question had already left before I could ask him. Totally agreed on the training, TDI it shall be.

Interesting views here

I would personally be conducting my own dive plan and then asking to see theirs to compare their expectations to mine. If they are being what I would consider 'overly-optimistic' with their SAC and bottom time plans then I would have serious misgivings about joining the dive at all. I might also have an opinion form about the centre allowing that to happen without a checkout dive or dive plan check. That being said, not knowing the full facts (they may have done just this), I would however keep said opinion to myself pending further evidence.

You are well within your rights to accept or decline a dive either way. When managing dives, I have happily cancelled dives wholesale because of local conditions at the site, and refused buddy pair's plans if I felt they were unsafe or hadn't been planned properly. With deco dives I expect a reasonable level of detail when I am briefed on the intentions and timeline of the dive. As a diver I have refused to enter the water with a renta-buddy on more than one occasion, owing to concerns over their fitness to dive. I've also had someone halt a dive before we entered because they were no longer confident in the plan and their abilities. That was fine - the plan was adjusted (shorter/shallower) until the diver was happy to continue.

If someone is not happy there is a reason - and that reason should always be addressed, even if the dive gets pulled

Safe Diving!

What you describe in your response is pretty much the reason I want to get more advanced training and experience. At this point in my diving life, I feel like I'm ill-equipped to execute those judgement calls (i.e. are they being over eager with the planned bottom plans, dive check plan, etc) By that I mean that up till PADI rescue diver we are not really trained to actually plan a dive. It's included in the manuals and theory but not practiced in training. In every PADI dive center I've ever been in so far, I am simply following the 'underwater tour guide'. I enter they water when they do, report my air when they ask, surface when they tell me to. Perhaps that experience will come with I get an actual dive buddy and we start diving without a dive center or when I do a DM course?

Divers who have not been trained for decompression dives, do not know what they do not know.

All dives are decompression dives. A recreational diver can blow a three minute safety stop or not hold the correct depth. However, once you go into decompression, the risks are exponential. A diver who has gone into decompression without the ability to maintain the stop at depth or does not have the gas for an unintended depth or time at depth risks getting hurt.

A recreational diver should not venture into decompression. You can and may get away it a number of times and it is "okay". We call this normalization of deviation. That's how sh_t hits the fan.

Get the training first. Like the cave divers sign says, "Nothing beyond this point is worth your life."

Safe diving

That resonates. It will go well a few times and then comes a time I might not surface... I really like to avoid that.

Some of the replies on here are absolutely bonkers. People should not be advocating that it is okay for just a "little deco" dive for the average, not decompression trained recreational diver. There is no such thing as "lite deco." 10 minutes of deco is NOT SAFE if you are not trained for decompression. Neither is 5 minutes, etc. Going into decompression essentially creates an imaginary hard overhead for the diver. Would it be okay to recommend the average recreational diver without cave training do just a "lite cave" dive. Only 10 minutes in an overhead. No big deal?

So much can go wrong doing decompression even with a trained diver, not to mention an untrained diver who has no clue what they do not know. It's not about decompressing on air or not. Are you sure you have enough air for your decompression? What if you go deeper or stay longer than planned? Do you have enough air for that? What if you lose gas or free flow? Does your buddy have enough air for you to deco on? Are you going to be able to maintain your buoyancy during deco if something happens like loss of gas or free flow? What about when you lose your mask and can't read your gauge to conduct deco properly? Do you have all the redundant gear you need? You're now in a hard overhead that if you ascend above you are seriously risking your life.

Yikes, I'm definitely not trained for most of those possible issues that could arise. Being on the spot when being in a dive center presented with a dive those are not things that pop to my mind. However, reading them here puts the situation into perspective. TDI here I come.

Most people tend to shy away from things that are potentially dangerous if they "don't know what they don't know". There is nothing wrong with that. You might call it "fear, uncertainty and doubt" but I would call it wisely respecting your limits and comfort zone.

So why do *I* think most people avoid doing simple deco dives? I think they do so because they recognize, perhaps passively, that it's a complication with (to them) unknown risks and they probably estimate that "it's not worth it".
R..

Indeed. One of the reasons I posted is that I fear going past my limits and losing control for reasons I'm uncertain about. I'm well aware that I don't know what I don't know and fear of that very unknown gave me a bad after taste because I foolishly agreed knowing I should not have.

Due to my lack of experience (<100 dives right now without ever planning one) I can't comment much on the discussion of the virtues, pitfalls, dangers and other issues related to the deco and going past your training and what is normal and what is not other than stating the obvious... However, I really appreciate seeing the discussion unfold here and seeing all the differing opinions. One thing is for sure... I'm looking forward to technical training at some point in the future so I can finally see what all the hubub is at 45m.

 

[boulderjohn]

What you describe in your response is pretty much the reason I want to get more advanced training and experience. At this point in my diving life, I feel like I'm ill-equipped to execute those judgement calls (i.e. are they being over eager with the planned bottom plans, dive check plan, etc) By that I mean that up till PADI rescue diver we are not really trained to actually plan a dive. It's included in the manuals and theory but not practiced in training. In every PADI dive center I've ever been in so far, I am simply following the 'underwater tour guide'.

It has nothing to do with the agency.

What you described is true of most dive operators in resort areas of the world. That is how they prefer to operate.That creates a problem for possibly most divers in the world. They get the initial training for how to plan a dive, and then they go out and do all their diving with operators who do everything for them. Before long, they have forgotten everything about dive planning they learned in class, including how to set up their own gear. I have had students tell me in their OW classes that their experienced diver friends told them they could forget all the dive planning stuff they are required to do in class, because once they were out in the real world, all of that is done for them.

I was a victim of that myself. I learned to dive and then went to Cozumel for all my diving for a couple of years. There everything is indeed done for you. Then I got on a boat in Florida and sat around waiting for someone to set up my gear until I finally realized I had to do it myself. It was really tough because I had not done it since my certification dives.

In other places, you are more on your own. In Florida, where I am at this very minute, on my dives I get on the boat with my gear and my tanks, set everything up, plan my dives, get in the water once the DM says the pool is open, come up when my dive is done, get on board, and break down my gear while the boat heads back to the shop.

What I just described in Florida is a PADI shop, so how operators work is based on the standard practices of that location, not on the agency involved.

 

[Edward3c]

... By that I mean that up till PADI rescue diver we are not really trained to actually plan a dive. It's included in the manuals and theory but not practiced in training. In every PADI dive center I've ever been in so far, I am simply following the 'underwater tour guide'. I enter they water when they do, report my air when they ask, surface when they tell me to. Perhaps that experience will come with I get an actual dive buddy and we start diving without a dive center or when I do a DM course?
...

Whenever I’ve asked PADI about two OW or AOW diving independently (without surface support) they consistently tell me the OW course teaches them all they need to know to safely plan a dive. Its interesting, you describe an alternative opinion.

 

[boulderjohn]

Whenever I’ve asked PADI about two OW or AOW diving independently (without surface support) they consistently tell me the OW course teaches them all they need to know to safely plan a dive. Its interesting, you describe an alternative opinion.

You are both confusing the training the students get when they are certified with the dive operations they then go to on their vacations around the world. The training is indeed supposed to prepare them to dive independently, but if they go to places that do not allow that for their diving, all that learning will eventually go away.

 

[eelnoraa]

I think officially, it is what supposed to be. But in reality, the rule with PADI is very loosely interpreted or enforced. if you hit a good instructor, which is highly rare, you will meet the standard that is supposed to be. But more likely than not, OW and AOW is just a mill for get a card. I personally experienced this. After AOW, I didn't think i have nearly enough knowledge and skill to plan and execute dive independently. Sure all the dives I did in those period came out OK, but didn't means I did them right.

 

[wbatten1]

Sorry for not posting earlier, I had to wait for my deco stop to end before I could respond...

nice.

SAC, cuft, I need to look up those terms. I think that presents the problem right? I.e. I definitely need training. Planning do go TDI once I hit 250 dives.

SAC = Surface Air Consumption. cuft = Cubic Foot (or Cubic Feet). Lots of folks use SAC incorrectly and actually mean RMV. RMV = Respiratory Minute Volume. SAC is measured in pressure whereas RMV is measured in volume. For purposes of understanding how SAC/RMV can be important, I'm going to use RMV.

If I have an RMV of .8 cuft, I would consume .8 cubic feet of air every minute while breathing at the surface. That would mean I would consume a standard aluminum 80 tank, which holds 80 cuft of air, in 100 minutes assuming I was breathing it on the surface. (Actually, an AL80 holds slightly under 80cuft of air, and that would affect calculating RMV, but that's another discussion.) Some food for thought- if an 80cuft tank lasts you 100 minutes on the surface, Boyle's law tells us that the same tank would last 50 minutes at 33 ft in sea water (fsw), or 1/2 as long. At 66fsw, it would last a third of what it does at the surface, or 33 minutes. 99ft, the tank would last 25 minutes, or 1/4 as long. So on and so forth. At 150ft, that's about 18 minutes of air before your tank is empty.

I don't know where you're at, but FWIW, I'd dive with you anytime. I appreciate divers who have respect for their limitations.

 

[Patoux01]

I think officially, it is what supposed to be. But in reality, the rule with PADI is very loosely interpreted or enforced. if you hit a good instructor, which is highly rare, you will meet the standard that is supposed to be.

To be honest, I have not had a buddy that was incompetent (in terms of standard) in the various places I've dived, even the ProDive lads were still buddy-able in the PADI term. They all knew the basics to survive.

There's only very few that met my standards of "someone I'd really want to dive with", but that is because I'm kind of maniac


During AOW we were required to do our final dive (shallow) with only our buddy, plan it, run it, and come back to the boat alive. Each pair of buddies going in a different direction. While we failed miserably on finding the boat at the end, we managed to do a dive without dying without our hands held.

I'm not gonna go over my OW that had me scootering around at 15m and some deeper drops, that'd get me in danger here

 

[Edward3c]

You are both confusing the training the students get when they are certified with the dive operations they then go to on their vacations around the world. The training is indeed supposed to prepare them to dive independently, but if they go to places that do not allow that for their diving, all that learning will eventually go away.

I'm sure the PADI syllabus covers dive planning, but in the 7 years of running monthly open water training sessions. The normal comment I get from PADI trained divers wanting to gain the BSAC Sports Diver qualification, is "I've never been shown how to plan a dive". Therefore, we go back and do the Ocean Diver theory and practical lessons on dive management. As Sports Divers they will be expected to be Assistant Dive Managers.