Planned deco on a recreational dive?

[Wookie]

Interesting question.. I've always had the preferred plan, which doesn't limit depth. I don't recall hearing / reading anything about the policy being voided because I dove below my certification level.
Did I miss some fine print?

There are no depth or training limitations on DAN policies that I am aware of.

 

[Centrals]

So, I've been diving at this great little dive center. Feels like a second home, great people, interesting dive sites blah blah. The other day a group of divers show up. They all have around 500 dives (way more than me for now) and seemed reasonably experienced.They are all have PADI rescue rating (like me). Next thing I know they've requested a 45 meter dive and plan to go into deco (aiming for 10 minutes deco stop max). I'm also scheduled for this dive. Now here's the hitch, only 1 person is actually a tech diver and it's not one of the customers. I said yes to the dive because a few minutes of deco didn't seem too serious and I've accidentally gone into deco twice so I had an idea of what to expect when it comes to understanding what my computer is telling regarding deco. However, due to some circumstances the dive never actually happened.

A responsible dive centre would have never sanction such a dive.
1. A planned deco dive is a tec dive.
2. 45m is way beyond recommended recreational dive limit.
3. What is your gas management for the dive?

 

[Centrals]

There are no depth or training limitations on DAN policies that I am aware of.

There is depth and training limit for DAN SEAP.

 

[Kevrumbo]

No I was only giving reference to the OP that the MGR minimum gas reserve for a 45 meter dive would be 63 cu/ft of gas. MGR is a volume of gas required for two divers to ascend from the bottom to the first available gas source or the surface , the plan assumes an emergency gas sharing scenario. I'm not sure how many cu/ft of gas is in a 12L tank I do know an AL80 hold 77 cu/ft so you can see my concern.

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.

...I still don't know what to make of the whole situation. Am I being a scuba prude for having this leave a bad after-taste in my mouth? I mean, I was not planning to venture into the technical realm just yet. As a recreational diver I am inclined to stick to the limits suggested by PADI. 5 meters deeper than 40 just because its more thrilling (or whatever their reasoning) seems like asking for trouble to me. Am I alone in these thoughts? Feel like I'm on a rant here, but I'm very curious if this is an exception or if this actually happens a lot in dive centers (i.e. customers asking to dip their toes a little beyond the recreational realm (especially when it comes to depth and deco stops) and dive centers agreeing.

..I feel comfortable with my limited experience at 40m. We were set to use 15 liter tanks. Those are the only things I knew were in place. Planning was likely in the form of the divemaster knowing what he was doing and the rest blindly following him (an assumption). I didn't see any DecoPlanners materialize...

The dive site has some interesting geological formations but nothing super spectacular. Definitely not in the spectacular way of Truk Lagoon. From the feedback I gathered at the dive center, those divers just wanted to do it for the sake of doing it. I wouldn't know how to handle Davy Jones outside of the recreational realm. I don't want to deal with Davy Jones.. :/

It's good to hear others say this verbatim. Until I'm tech trained, walk away I shall.

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.

 

[Vicko]

It depends on the dive and the customers involved.
Will I do a 10 minute deco on the line with people who have bad buoyancy? No.
Will I do 10 minutes of deco while cruising along the shallows with just about anybody who agrees to it? If we are taking enough air (no gas switching involved), yes.

I don't understand why are people so afraid of doing simple deco dives, or refuse to do deco on air. I am in no way implying you should have done the dive, if you don't feel comfortable with doing the dive there are no reasons to do it then, but I also think that with a bit of solo learning you can calculate how much gas reserve you need and how to do a deco dive safely, and then enjoy some of the deeper/longer dives.

 

[tursiops]

I also think that with a bit of solo learning you can calculate how much gas reserve you need and how to do a deco dive safely, and then enjoy some of the deeper/longer dives.

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

 

[dirkadirk]

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!

 

[Edward3c]

....
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.
...

My understanding is the rule of thirds is one-third out, one-third in and one-third resurve, I.e. you surface with at least the last third.

I just ran this through our tables and get a 2 min stop @ 6m and still susface with over 150bar

At 17Lt/ min I would look at doing 20 at depth with 1min @ 9m and 3 @ 6m, and surface with more than the one-third resurve. Note: I dive on 300bar 12Lt so this would be a normal dive, if I could be bothered going that deep.

 

[Chris12day]

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

 

[eelnoraa]

45m dive, single tank, air, a group of divers, this is nut. I am surprised the so called tec trained diver agree to this.