Rebreather World - View Single Post - What setpoint for 100m+ diving do you use?

Drmike · 13th February 2008, 03:17

High inspired ppHe and high retained CO2 are contributors to O2 tox

On deep dives does running high ppo2s at depth offer any significant deco advantage? - increasingly (As you go deeper) no

on deep dives you are using high ppHe and likely enjoying higher retained CO2 (due to a) rapid descents, b) higher gas densities c) respiratory issues associated with high ambient pressures, wob ect) Do you really want to be breathing high PPO2s during times of high ppHE and higher CO2? especially when the higher ppo2 offers little to no deco advantage?

Getting down to depth is often a time of exertion. do you really want to be breathing high ppO2 at depth during times of high exertion??

How long does it take to reach depth? Not long if doing typical bounce dive

Fast descent speeds with high setpoint is recipe for ppop2 overshoot during descent (especially if using rich dil) as well as poor lung ventilation

What I do is split the dive into sections and determine empirically the optimum setopiont for each stage:

The 1st draft using v-planner is done by temp setting a deco baseline of setpoint 1.3 from start of bottom time up to 6m then O2. (ignoring for time being CNS)

Now I plug in different setpoints for descent and see how that affects deco time. 99% of the time (with anything but the very slowest descents, or if cave) the start and descent ppo2 has no effect on deco so Id start with a low one - say 1.0. This also prevents spiking of poo2 on descent and helps minimise O2 tix risk (see above)

Now (assuming descent setpoint of 1.0 1.3 for ascent and O2 at 6m) I look at the bottom setpoint. I plug in different bottom ppo2s to see effect on deco. Depending on depth and BT high ppo2s often add little to nothing to deco (I consider a 30min reduction in deco nothing when balanced against O2 risk)

Lets say bottom time is relatively short as we are deep increasingly hiher setpionts offer min to non deco advanteg so perhaps a setpoint of 1.1 is reasonable.

Now I look at ascent.

Usually what I do is split the ascent into sections and play around with increasing setpoint at various depths in stages to find optimum depth/setpoint increase. No point (for eg) running 1.3 from 100m upwards if I can get sane deco time running say 1.1 up to 60m, 1.2 to 30m and 1.3 from 20m - as way of example)

By way of quick example:

same dive but one with optimized setpoint switching:-

Dec to 110m (5:30) Diluents 7/70 1.30 SetPoint, 20m/min descent.
Dec to 125m (6:15) Diluent 7/70 1.30 SetPoint, 20m/min descent.
Dec to 150m (7:55) Diluent 7/70 1.30 SetPoint, 15m/min descent.
Level 150m 12:05 (20:00) Diluent 7/70 1.30 SetPoint, 36m ead, 39m end
Asc to 126m (22:24) Diluent 7/70 1.30 SetPoint, -10m/min ascent.
Stop at 120m 1:06 (23:30) Diluent 7/70 1.30 SetPoint, 26m ead, 32m end
Stop at 114m 1:00 (24:30) Diluent 7/70 1.30 SetPoint, 24m ead, 30m end
Stop at 108m 1:30 (26:00) Diluent 7/70 1.30 SetPoint, 23m ead, 29m end
Stop at 102m 1:30 (27:30) Diluent 7/70 1.30 SetPoint, 21m ead, 27m end
Stop at 96m 1:30 (29:00) Diluent 7/70 1.30 SetPoint, 19m ead, 26m end
Stop at 90m 2:00 (31:00) Diluent 7/70 1.30 SetPoint, 17m ead, 24m end
Stop at 84m 2:30 (33:30) Diluent 7/70 1.30 SetPoint, 15m ead, 23m end
Stop at 78m 2:30 (36:00) Diluent 7/70 1.30 SetPoint, 13m ead, 21m end
Stop at 72m 3:30 (39:30) Diluent 7/70 1.30 SetPoint, 11m ead, 20m end
Stop at 66m 3:30 (43:00) Diluent 7/70 1.30 SetPoint, 9m ead, 19m end
Stop at 60m 5:30 (48:30) Diluent 7/70 1.30 SetPoint, 8m ead, 17m end
Stop at 54m 5:00 (53:30) Diluent 7/70 1.30 SetPoint, 6m ead, 16m end
Stop at 48m 7:30 (61:00) Diluent 7/70 1.30 SetPoint, 4m ead, 14m end
Stop at 42m 9:00 (70:00) Diluent 7/70 1.30 SetPoint, 2m ead, 13m end
Stop at 36m 11:00 (81:00) Diluent 7/70 1.30 SetPoint, 0m ead, 11m end
Stop at 30m 15:30 (96:30) Diluent 7/70 1.30 SetPoint, 0m ead, 10m end
Stop at 24m 22:30 (119:00) Diluent 7/70 1.30 SetPoint, 0m ead, 8m end
Stop at 18m 35:30 (154:30) Diluent 7/70 1.30 SetPoint, 0m ead, 7m end
Stop at 12m 61:30 (216:00) Diluent 7/70 1.30 SetPoint, 0m ead, 5m end
Stop at 6m 110:30 (326:30) Oxygen 1.58 ppO2, 0m ead
Surface (327:06) Oxygen -10m/min ascent.
Off gassing starts at 129.5m
OTU's this dive: 530
CNS Total: 283.2%
2617.0 ltr Oxygen
2617 ltr OC TOTAL

Dec to 110m (5:30) Diluent 7/70 1.00 SetPoint, 20m/min descent.
Dec to 125m (6:15) Diluent 7/70 1.00 SetPoint, 20m/min descent.
Dec to 150m (7:55) Diluent 7/70 1.00 SetPoint, 15m/min descent.
Level 150m 12:05 (20:00) Diluent 7/70 1.10 SetPoint, 36m ead, 38m end
Asc to 126m (22:24) Diluent 7/70 1.20 SetPoint, -10m/min ascent.
Stop at 120m 1:06 (23:30) Diluent 7/70 1.20 SetPoint, 27m ead, 31m end
Stop at 114m 1:00 (24:30) Diluent 7/70 1.20 SetPoint, 25m ead, 30m end
Stop at 108m 1:30 (26:00) Diluent 7/70 1.20 SetPoint, 23m ead, 28m end
Stop at 102m 2:00 (28:00) Diluent 7/70 1.20 SetPoint, 21m ead, 27m end
Stop at 96m 1:30 (29:30) Diluent 7/70 1.20 SetPoint, 19m ead, 25m end
Stop at 90m 2:30 (32:00) Diluent 7/70 1.20 SetPoint, 17m ead, 24m end
Stop at 84m 2:30 (34:30) Diluent 7/70 1.20 SetPoint, 15m ead, 22m end
Stop at 78m 3:00 (37:30) Diluent 7/70 1.20 SetPoint, 13m ead, 21m end
Stop at 72m 3:30 (41:00) Diluent 7/70 1.20 SetPoint, 12m ead, 19m end
Stop at 66m 4:30 (45:30) Diluent 7/70 1.20 SetPoint, 10m ead, 18m end
Stop at 60m 5:00 (50:30) Diluent 7/70 1.30 SetPoint, 8m ead, 17m end
Stop at 54m 6:00 (56:30) Diluent 7/70 1.30 SetPoint, 6m ead, 16m end
Stop at 48m 7:30 (64:00) Diluent 7/70 1.30 SetPoint, 4m ead, 14m end
Stop at 42m 9:30 (73:30) Diluent 7/70 1.30 SetPoint, 2m ead, 13m end
Stop at 36m 11:30 (85:00) Diluent 7/70 1.30 SetPoint, 0m ead, 11m end
Stop at 30m 16:30 (101:30) Diluent 7/70 1.30 SetPoint, 0m ead, 10m end
Stop at 24m 23:30 (125:00) Diluent 7/70 1.30 SetPoint, 0m ead, 8m end
Stop at 18m 37:00 (162:00) Diluent 7/70 1.30 SetPoint, 0m ead, 7m end
Stop at 12m 65:30 (227:30) Diluent 7/70 1.30 SetPoint, 0m ead, 5m end
Stop at 6m 125:30 (353:00) Diluent 7/70 1.45 SetPoint, 0m ead, 5m end
Surface (353:36) Diluent 7/70 -10m/min ascent.
Off gassing starts at 132.1m
OTU's this dive: 540
CNS Total: 212.1%

Optimised setpoint switching gives me similar run times but with setpoint switching I am on much lower (safer) ppo2 at depth I dont fry my lungs on 1.6 during deco thety remain efficenr for offgassing and overall reduction in CNS (if you think that means anything)

Id rather have 30m longer deco for a drop in setpoint of just 0.1 at the bottom than not.

13th February 2008, 03:17	#22 (permalink)
Drmike Custom Title Allowed! Current Rebreather/s: MK 15.X Ouroboros Other CCR Home Build Other Rebreather/s: Inspiration Classic Other CCR Home Build Join Date: Feb 2005 Posts: 3,303	Re: What setpoint for 100m+ diving do you use? High inspired ppHe and high retained CO2 are contributors to O2 tox On deep dives does running high ppo2s at depth offer any significant deco advantage? - increasingly (As you go deeper) no on deep dives you are using high ppHe and likely enjoying higher retained CO2 (due to a) rapid descents, b) higher gas densities c) respiratory issues associated with high ambient pressures, wob ect) Do you really want to be breathing high PPO2s during times of high ppHE and higher CO2? especially when the higher ppo2 offers little to no deco advantage? Getting down to depth is often a time of exertion. do you really want to be breathing high ppO2 at depth during times of high exertion?? How long does it take to reach depth? Not long if doing typical bounce dive Fast descent speeds with high setpoint is recipe for ppop2 overshoot during descent (especially if using rich dil) as well as poor lung ventilation What I do is split the dive into sections and determine empirically the optimum setopiont for each stage: The 1st draft using v-planner is done by temp setting a deco baseline of setpoint 1.3 from start of bottom time up to 6m then O2. (ignoring for time being CNS) Now I plug in different setpoints for descent and see how that affects deco time. 99% of the time (with anything but the very slowest descents, or if cave) the start and descent ppo2 has no effect on deco so Id start with a low one - say 1.0. This also prevents spiking of poo2 on descent and helps minimise O2 tix risk (see above) Now (assuming descent setpoint of 1.0 1.3 for ascent and O2 at 6m) I look at the bottom setpoint. I plug in different bottom ppo2s to see effect on deco. Depending on depth and BT high ppo2s often add little to nothing to deco (I consider a 30min reduction in deco nothing when balanced against O2 risk) Lets say bottom time is relatively short as we are deep increasingly hiher setpionts offer min to non deco advanteg so perhaps a setpoint of 1.1 is reasonable. Now I look at ascent. Usually what I do is split the ascent into sections and play around with increasing setpoint at various depths in stages to find optimum depth/setpoint increase. No point (for eg) running 1.3 from 100m upwards if I can get sane deco time running say 1.1 up to 60m, 1.2 to 30m and 1.3 from 20m - as way of example) By way of quick example: same dive but one with optimized setpoint switching:- Dec to 110m (5:30) Diluents 7/70 1.30 SetPoint, 20m/min descent. Dec to 125m (6:15) Diluent 7/70 1.30 SetPoint, 20m/min descent. Dec to 150m (7:55) Diluent 7/70 1.30 SetPoint, 15m/min descent. Level 150m 12:05 (20:00) Diluent 7/70 1.30 SetPoint, 36m ead, 39m end Asc to 126m (22:24) Diluent 7/70 1.30 SetPoint, -10m/min ascent. Stop at 120m 1:06 (23:30) Diluent 7/70 1.30 SetPoint, 26m ead, 32m end Stop at 114m 1:00 (24:30) Diluent 7/70 1.30 SetPoint, 24m ead, 30m end Stop at 108m 1:30 (26:00) Diluent 7/70 1.30 SetPoint, 23m ead, 29m end Stop at 102m 1:30 (27:30) Diluent 7/70 1.30 SetPoint, 21m ead, 27m end Stop at 96m 1:30 (29:00) Diluent 7/70 1.30 SetPoint, 19m ead, 26m end Stop at 90m 2:00 (31:00) Diluent 7/70 1.30 SetPoint, 17m ead, 24m end Stop at 84m 2:30 (33:30) Diluent 7/70 1.30 SetPoint, 15m ead, 23m end Stop at 78m 2:30 (36:00) Diluent 7/70 1.30 SetPoint, 13m ead, 21m end Stop at 72m 3:30 (39:30) Diluent 7/70 1.30 SetPoint, 11m ead, 20m end Stop at 66m 3:30 (43:00) Diluent 7/70 1.30 SetPoint, 9m ead, 19m end Stop at 60m 5:30 (48:30) Diluent 7/70 1.30 SetPoint, 8m ead, 17m end Stop at 54m 5:00 (53:30) Diluent 7/70 1.30 SetPoint, 6m ead, 16m end Stop at 48m 7:30 (61:00) Diluent 7/70 1.30 SetPoint, 4m ead, 14m end Stop at 42m 9:00 (70:00) Diluent 7/70 1.30 SetPoint, 2m ead, 13m end Stop at 36m 11:00 (81:00) Diluent 7/70 1.30 SetPoint, 0m ead, 11m end Stop at 30m 15:30 (96:30) Diluent 7/70 1.30 SetPoint, 0m ead, 10m end Stop at 24m 22:30 (119:00) Diluent 7/70 1.30 SetPoint, 0m ead, 8m end Stop at 18m 35:30 (154:30) Diluent 7/70 1.30 SetPoint, 0m ead, 7m end Stop at 12m 61:30 (216:00) Diluent 7/70 1.30 SetPoint, 0m ead, 5m end Stop at 6m 110:30 (326:30) Oxygen 1.58 ppO2, 0m ead Surface (327:06) Oxygen -10m/min ascent. Off gassing starts at 129.5m OTU's this dive: 530 CNS Total: 283.2% 2617.0 ltr Oxygen 2617 ltr OC TOTAL Dec to 110m (5:30) Diluent 7/70 1.00 SetPoint, 20m/min descent. Dec to 125m (6:15) Diluent 7/70 1.00 SetPoint, 20m/min descent. Dec to 150m (7:55) Diluent 7/70 1.00 SetPoint, 15m/min descent. Level 150m 12:05 (20:00) Diluent 7/70 1.10 SetPoint, 36m ead, 38m end Asc to 126m (22:24) Diluent 7/70 1.20 SetPoint, -10m/min ascent. Stop at 120m 1:06 (23:30) Diluent 7/70 1.20 SetPoint, 27m ead, 31m end Stop at 114m 1:00 (24:30) Diluent 7/70 1.20 SetPoint, 25m ead, 30m end Stop at 108m 1:30 (26:00) Diluent 7/70 1.20 SetPoint, 23m ead, 28m end Stop at 102m 2:00 (28:00) Diluent 7/70 1.20 SetPoint, 21m ead, 27m end Stop at 96m 1:30 (29:30) Diluent 7/70 1.20 SetPoint, 19m ead, 25m end Stop at 90m 2:30 (32:00) Diluent 7/70 1.20 SetPoint, 17m ead, 24m end Stop at 84m 2:30 (34:30) Diluent 7/70 1.20 SetPoint, 15m ead, 22m end Stop at 78m 3:00 (37:30) Diluent 7/70 1.20 SetPoint, 13m ead, 21m end Stop at 72m 3:30 (41:00) Diluent 7/70 1.20 SetPoint, 12m ead, 19m end Stop at 66m 4:30 (45:30) Diluent 7/70 1.20 SetPoint, 10m ead, 18m end Stop at 60m 5:00 (50:30) Diluent 7/70 1.30 SetPoint, 8m ead, 17m end Stop at 54m 6:00 (56:30) Diluent 7/70 1.30 SetPoint, 6m ead, 16m end Stop at 48m 7:30 (64:00) Diluent 7/70 1.30 SetPoint, 4m ead, 14m end Stop at 42m 9:30 (73:30) Diluent 7/70 1.30 SetPoint, 2m ead, 13m end Stop at 36m 11:30 (85:00) Diluent 7/70 1.30 SetPoint, 0m ead, 11m end Stop at 30m 16:30 (101:30) Diluent 7/70 1.30 SetPoint, 0m ead, 10m end Stop at 24m 23:30 (125:00) Diluent 7/70 1.30 SetPoint, 0m ead, 8m end Stop at 18m 37:00 (162:00) Diluent 7/70 1.30 SetPoint, 0m ead, 7m end Stop at 12m 65:30 (227:30) Diluent 7/70 1.30 SetPoint, 0m ead, 5m end Stop at 6m 125:30 (353:00) Diluent 7/70 1.45 SetPoint, 0m ead, 5m end Surface (353:36) Diluent 7/70 -10m/min ascent. Off gassing starts at 132.1m OTU's this dive: 540 CNS Total: 212.1% Optimised setpoint switching gives me similar run times but with setpoint switching I am on much lower (safer) ppo2 at depth I dont fry my lungs on 1.6 during deco thety remain efficenr for offgassing and overall reduction in CNS (if you think that means anything) Id rather have 30m longer deco for a drop in setpoint of just 0.1 at the bottom than not. __________________ Cave diving is a sport Wreck diving is a sport Diving in general is a sport 'Rebreather diving' is not a sport its the delusional obsession with a highly dangerous and often inappropriate piece of equipment Last edited by Drmike : 13th February 2008 at 03:48.
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