Diver one of sixteen to die using high-tech gear

[Groovekitty]

Divermole,

Thanks for the info - it's nice to hear your point of view.

What do you think about the story that started this thread? I'm assuming you practise good buddy techniques, but in the scenario presented in the article, apparently there was no buzzer going off (granted the buddy may have been off in Timbukto and never heard it - but you did mention that it is ear-splitting) - what do you think about a scenario where the alarm malfunctions, thus your CCR has the ability to deliver a hit of O2 at depth?

It seems this may have been what occurred in the dive in question.

~groovekitty*

[DiverMole]

I use constant Po2 tables (DDplan) for pre-work and backups and then a VR3 on the actual dive which actually runs the deco in real time using your loop PPO2

For 60m at 20mins I would do the following

The Drogon Dive Planner [default] v2.15

The Drogon Dive Planner [v2:15]
========================================

Dive profile for default:
Step Depth SegT RunT Gas ppO2 END
===============================================================
1 0.0-> 60.0 4:00 4:00 Trimix 10/33 0.70 41
2 60.0-> 60.0 20:00 24:00 Trimix 19/30 1.30 36

Deepest effective stop: 42m
Buhlmann + Gradient Factor decompression schedule:
Step Depth SegT RunT %MV Gas ppO2 END
===============================================================
3 60.0-> 30.0 4:00 28:00 65.7 Trimix 32/25 1.30 12
4 30.0-> 27.0 1:00 29:00 67.3 Trimix 35/24 1.30 9
5 27.0-> 24.0 1:00 30:00 70.5 Trimix 38/23 1.30 7
6 24.0-> 21.0 1:00 31:00 73.9 Trimix 42/21 1.30 4
7 21.0-> 18.0 2:00 33:00 77.8 Trimix 46/20 1.30 2
8 18.0-> 15.0 2:00 35:00 79.5 Trimix 52/18 1.30 0
9 15.0-> 12.0 3:00 38:00 82.4 Trimix 59/15 1.30 0
10 12.0-> 9.0 5:00 43:00 84.8 Trimix 68/12 1.30 0
11 9.0-> 6.0 2:00 45:00 86.8 Trimix 81/ 7 1.30 0
12 6.0-> 5.0 16:00 61:00 87.1 Trimix 87/ 5 1.30 0
13 5.0-> 0.0 0:30 61:30 91.4
===============================================================
Dive time: 0:24:00 Gradient Factors were used:
Ascent & Deco time: 0:37:30 Low factor: 30%
======== High factor: 80%
Total run time: 1:01:30

Ascent rate: 10, Descent rate: 15 (m/min) Total CNS: 33% OTUs: 87

CC Setpoints used:
Depth Setpoint CNS
==========================
* 32.6 CC CNS Total: 33%


In the Nic Gotto case the Inquest is being held this week. Provisionally it looks like operator error. He had 8 hours use on his scrubber which is rated for 3 hours. There would be no warning from the computers for hypercapnia as its not related to PPO2. If this is true there is no one to blame but Nic himself

Real shame and my condolenses to those involved

[DRE]

A comparison of the 200 for 20 on OC:

I use GUE's D-plan (the Palm version of Decoplanner) to calculate my profiles, Low GF: 20 High GF: 80.

Bottom gas: 18/45 (pO2 of 1.3, END of 95ft)
Deco gasses EAN 50 and O2

D-plan includes descent time into the profile, so I'll be leaving the bottom at 20 instead of 24.

fsw min run mix pO2
200 20 20 18/45 1.3
110 1 23 18/45 0.8
100 1 24 18/45 0.7
90 2 26 18/45 0.7
80 2 28 18/45 0.6
70 3 31 50% 1.6
60 1 32 50% 1.4
50 1 33 50% 1.1
40 4 37 50% 1.0
30 5 42 50% 1.0
20 19 61 O2 1.6


As you can see this schedule gets me out of the water as quickly as the constant Po2 profiles of the Inspiration. The only benefit the CCR has over OC is that the volume of gas used (not necessarily gas carried, as Divermole pointed out in his previous postings using the 7L/46cf tanks plus bailout and the size of the rebreather gives you about the same profile as OC) is a lot smaller in case nothing goes wrong. To do this dive safely on OC in terms of bailout gas you need a minimum of double AL80's with 2 AL 30's for deco gas.

[DiverMole]

But you used a different gradient factor so of course you get out quicker and you are using different software with a much less conservative algorythm. You also used a different mix.

But yes, the profiles are pretty similar as you are doing a nice square profile. Its when you do a multi profile and the OC guys are not sitting at a high set point that it pays off

On very square dives the OC guys often run 1.4 bar and hence get less deco than us, but we catch up on the way up as we run a better mix all the way.

But we get warm moist gas, silence and a lot more reserve gas in case of problems (approx 20 hours in the 7l) and I would use approx 30 bar of O2 on this dive from a 7L so could do the same dive again several times without a refill, and I'd be caryying no side slung stages, its all on my back and slightly lighter than your twinset ;D

[beeger]

DiverMole - I asked this ealier but I think my post was missed. What brings you to the mnscuba site (assuming you are writing from the UK)? You seem quite fond of the Inspiration, and very versed in its use and practice. With all the rebreather forums out there, how did you end up here?

[Punky]

Forgive me if I sound dumb but what are;
VR3
OC/DSV
DV
PO2 & PPO2 [I know they pertain to oxygen but ?]

I find this discussion interesting but when you don't speak the
speak it's harder to follow.

[DiverMole]

Did a search on google/Yahoo and found a reference to Rebreathers here. I run a rebreather website so am interested in what is said about them. Come here and the rest is history!!

You'll find me on most forums with a rebreather or technical section

Yes, I'm a limey from London.

Take a look at to find out more about me

[DiverMole]

VR3 is a very good dive computer that can have an oxygen cell fitted

OC/DSV is an Open Circuit/Diver Submersible Valve. ie a mouthpiece with an open circuit demand valve built in

DV is Demand Valve, the old name for a regulator

PO2 and PPO2 are the same thing, Partial Pressure of Oxygen

OC is open circuit CC is closed circuit

Sorry I forget most dont use these terms on a daily basis

[john j]

If you want a fair comparison of OC to CCR deco times, you have to use the same gases in each case to gauge the deco advantages of CCR. If I I did a dive on a CCR using the same gases you just did, the total deco time would be 31 minutes compared to your 41 minutes for OC. In addition, I would have never exposed myself to a 1.6PO2 like you did. (V-planner table shown below). Considering how cold the water is in Superior, I'd be very pleased with a 10 minute reduction in deco time, which by the way makes the dive safer in some aspects than OC. That comes out to almost 25% less deco time on this dive on CCR comapared to OC.

Another huge advantage is that with one fill of my CCR and bailout bottles, I could repeat this dive about 4 or 5 times without ever having to switch tanks or get any fills. That's a huge benefit in my practice. Furthermore, if I decided to do a shallower dive during the trip, I still would have optimized PO2 whereas you would not with the mixes you proposed. CCR's are extremely flexible.

Surface interval = 1 day 0 hr 0 min.
Altitude = 0ft
Conservatism = Nominal

Dec to 200ft   (4) on Diluent 18.0/45.0, 0.70 SetPoint, 50ft/min decent.
Level 200ft 16:00 (20) on Diluent 18.0/45.0, 1.30 SetPoint, 76ft END
Asc to 130ft   (21) on Diluent 18.0/45.0, 1.30 SetPoint, -60ft/min ascent.
Stop at 130ft 0:50 (22) on Diluent 18.0/45.0, 1.30 SetPoint, 43ft END
Stop at 120ft 1:00 (23) on Diluent 18.0/45.0, 1.30 SetPoint, 38ft END
Stop at 110ft 1:00 (24) on Diluent 18.0/45.0, 1.30 SetPoint, 34ft END
Stop at 100ft 1:00 (25) on Diluent 18.0/45.0, 1.30 SetPoint, 19ft END
Stop at 90ft 1:00 (26) on Diluent 18.0/45.0, 1.30 SetPoint, 15ft END
Stop at 80ft 2:00 (28) on Diluent 18.0/45.0, 1.30 SetPoint, 11ft END
Level 70ft 1:00 (29) on Diluent 50.0, 1.30 SetPoint, 44ft END
Asc to 60ft   (29) on Diluent 50.0, 1.30 SetPoint, -30ft/min ascent.
Stop at 60ft 1:40 (31) on Diluent 50.0, 1.30 SetPoint, 36ft END
Stop at 50ft 2:00 (33) on Diluent 50.0, 1.30 SetPoint, 29ft END
Stop at 40ft 3:00 (36) on Diluent 50.0, 1.30 SetPoint, 21ft END
Stop at 30ft 3:00 (39) on Diluent 50.0, 1.30 SetPoint, 14ft END
Level 20ft 1:00 (40) on Oxygen, 1.40 SetPoint, 0ft END
Stop at 20ft 4:00 (44) on Oxygen, 1.40 SetPoint, 0ft END
Stop at 10ft 7:00 (51) on Oxygen, 1.32 (1.40), 0ft END
Asc to sfc.   (51) on Oxygen, -30ft/min ascent.

NOTE - This Multi Level dive requires intermediate deco stops between levels.

OTU's this dive: 73
CNS Total: 27.7%

[DRE]

I misread - I thought you were using 80/20GF's, with 80/30GF's I get out in 59min.
As far as multilevel profiles are concerned, these can be calculated as well, and won't give a hugely different deco curve - you can even calculate them as separate dives and then look at what the leading tissue group is for any combination.
CCR's do not have an advantage over OC with regards to deco (depending on how you do your deco - I prefer using a combination of VPM and Buhlmann models instead of running straight Buhlmann, what is what you guys do).