Not diving to greater than 30m/100ft unless with helium

[dumpsterDiver]

I think it would be a more accurate estimation to say the psychological aspects would have compounded any physiological impacts.

I think this is true of anybody when their dive deviates from their dive plan to the point that it becomes psychologically impactful. It can be true for any number of situations. To what extent is of a personal nature.

I agree, and from everything we have heard, she was very much "by the book" with regard to safety. My point being, that a momentary exposure to 1.6 ATM of oxygen or a quick bounce and ascent from 130 would not be expected to cause oxygen toxicity or (obviously) residual narcosis, but she was probably "not happy" about it either.

 

[PfcAJ]

The simple answer is that adding He to the mix will always give you less no-deco time than without He.

Not so sure about that one...

 

[GrimSleeper]

What I came away with from a presentation by Doolette was that the gas model is as reported in his findings, but... it doesn't mean the added time is not in fact needed. Adding some conservatism doesn't hurt vs. riding the knives edge of deco obligations by omitting he from the algorithm.

Completely agree. It does make one wonder what 'truth' of diving will be overturned next, though...


Sent from my iPad using Tapatalk HD

 

[Searcaigh]

Not so sure about that one...

I concur

I frequently dive to 30M on a wreck over here on the east coast of UAE with EAN32, so I ran the numbers on Multideco to dive it with no deco gases and only using a 20/40 mix which is what I usually use for my deeper dives, and with air, see below;

DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 0m
Conservatism = GF 15/75


Dec to 30m (3) Trimix 20/40 10m/min descent.
Level 30m 27:00 (30) Trimix 20/40 0.80 ppO2, 10m ead, 14m end
Asc to 18m (32) Trimix 20/40 -6m/min ascent.
Stop at 18m 1:00 (33) Trimix 20/40 0.56 ppO2, 4m ead, 7m end
Stop at 15m 1:00 (34) Trimix 20/40 0.50 ppO2, 3m ead, 5m end
Stop at 12m 2:00 (36) Trimix 20/40 0.44 ppO2, 1m ead, 3m end
Stop at 9m 4:00 (40) Trimix 20/40 0.38 ppO2, 0m ead, 1m end
Stop at 6m 2:00 (42) Trimix 20/40 0.32 ppO2, 0m ead, 0m end
Stop at 5m 39:00 (81) Trimix 20/40 0.30 ppO2, 0m ead, 0m end
Surface (86) Trimix 20/40 -1m/min ascent.


OTU's this dive: 20
CNS Total: 6.7%

DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 0m
Conservatism = GF 15/75


Dec to 30m (3) Air 10m/min descent.
Level 30m 27:00 (30) Air 0.84 ppO2, 30m ead
Asc to 18m (32) Air -6m/min ascent.
Stop at 18m 1:00 (33) Air 0.59 ppO2, 18m ead
Stop at 15m 1:00 (34) Air 0.52 ppO2, 15m ead
Stop at 12m 1:00 (35) Air 0.46 ppO2, 12m ead
Stop at 9m 3:00 (38) Air 0.40 ppO2, 9m ead
Stop at 6m 1:00 (39) Air 0.34 ppO2, 6m ead
Stop at 5m 24:00 (63) Air 0.31 ppO2, 5m ead
Surface (68) Air -1m/min ascent.


OTU's this dive: 22
CNS Total: 7.6%


So, 86 mins using He and 68 mins using Air

Mmmm so does having an additional 1% O2 make much difference

DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 0m
Conservatism = GF 15/75


Dec to 30m (3) Triox 21/40 10m/min descent.
Level 30m 27:00 (30) Triox 21/40 0.84 ppO2, 10m ead, 14m end
Asc to 18m (32) Triox 21/40 -6m/min ascent.
Stop at 18m 1:00 (33) Triox 21/40 0.59 ppO2, 4m ead, 7m end
Stop at 15m 1:00 (34) Triox 21/40 0.52 ppO2, 2m ead, 5m end
Stop at 12m 1:00 (35) Triox 21/40 0.46 ppO2, 1m ead, 3m end
Stop at 9m 4:00 (39) Triox 21/40 0.40 ppO2, 0m ead, 1m end
Stop at 6m 2:00 (41) Triox 21/40 0.34 ppO2, 0m ead, 0m end
Stop at 5m 36:00 (77) Triox 21/40 0.31 ppO2, 0m ead, 0m end
Surface (82) Triox 21/40 -1m/min ascent.


OTU's this dive: 22
CNS Total: 7.6%

Not really, only 4 mins less deco, unless I have screwed up somewhere

 

[PfcAJ]

snip

So I fiddled with decoplanner a bit and ran some profiles for min-deco dives (no more than 1 min "stops"). With gfs of 20/85, I get 100ft for 20mins with 30/30 and 23mins with 30/00. 3mins difference is smaller than the NDL differences you get from PADI and NAUI tables.

pInert matters most, and there's at least a bit of research out there that suggests that helium based gases are better for deco purposes than nitrogen based gases.

Helium is less soluble than nitrogen, and gas solubility is a big thing in decompression. I don't get too wrapped up in my helium % when figuring out deco schedules.

 

[Germie]

Deco is no absolute science. So 3 minutes difference on a dive is not something to worry. Are you conservative, then stay 3 minutes longer. The padi ndl table is safe, the naui ndl table is safe, the cmas ndl table is safe. but none is same.
Helium ongases faster and offgases faster. The theory says this: So when nitrogen starts offgassing, you are still ongassing the helium. Mathematically this means a different deco-approach according to just diving on air. That is why diving a 20/80 mix gives really long decotimes according to diving a 21%/air. There are now some studies done that say the differences are not so big as the maths think/show, but as long as it is no absolute science we don't know. The buhlmann theory with GF as we use nowadays proofs that it is a safe way to caculate diveplans. So I respect it and use within this knowledge pragmatic deco, but I don't say easy take a 10/70 to 100m and some decogases and the plan is same as diving on air to 100m with same decogases. There is yet not enough proof that this aproach is safe. The buhlmann +GF approach is done now so much (even vpm-b) that you can say it is safe. But it does not say it is safe for every diver and every circumstances. So be a thinking diver. 30/85 works maybe for you, but not for another diver.
It is theoretically possible we dive in 10 years a new modell, but now I won't do that because of no proven technique.
Even now bounce dives are still controversial with their speeds to go up for example (you can go up as fast as possible up to the theoretically offgassing point for example, but if this is safe is not proven). From Buhlmann+GF it is said that it is 'safe' up to 100m, but a lot of divers use it successfull deeper. VPM-B+2 has shorter decotimes but more 'deepstops', and this was popular a few years ago and now more and more divers tend to skip the really deep deepstops. For me same, when I go to 100m, I don't do an 80m deepstop. My first stop of 1 minute is around 60m-66m. I do'nt plan myself with VPM-B. There is another theory about the difference of solubillity of nitrogen and helium. That can give you different decotimes too. But all it is a theoretically and mathematical approach and no absolute science.
The best advice if you want to do really deep/long decodives is learn to know your body. It does not give you any always safe information, but it can give you information what works for you. Why are some divers bent on a dive and others on the same dive not? No maths can tell you. No science can tell you. Otherwise no divers are bent anymore. We all know it never happens to us, but we don't know.

 

[ScubaInChicago]

Deco is no absolute science. So 3 minutes difference on a dive is not something to worry. Are you conservative, then stay 3 minutes longer. The padi ndl table is safe, the naui ndl table is safe, the cmas ndl table is safe. but none is same.
Helium ongases faster and offgases faster. The theory says this: So when nitrogen starts offgassing, you are still ongassing the helium. Mathematically this means a different deco-approach according to just diving on air. That is why diving a 20/80 mix gives really long decotimes according to diving a 21%/air. There are now some studies done that say the differences are not so big as the maths think/show, but as long as it is no absolute science we don't know. The buhlmann theory with GF as we use nowadays proofs that it is a safe way to caculate diveplans. So I respect it and use within this knowledge pragmatic deco, but I don't say easy take a 10/70 to 100m and some decogases and the plan is same as diving on air to 100m with same decogases. There is yet not enough proof that this aproach is safe. The buhlmann +GF approach is done now so much (even vpm-b) that you can say it is safe. But it does not say it is safe for every diver and every circumstances. So be a thinking diver. 30/85 works maybe for you, but not for another diver.
It is theoretically possible we dive in 10 years a new modell, but now I won't do that because of no proven technique.
Even now bounce dives are still controversial with their speeds to go up for example (you can go up as fast as possible up to the theoretically offgassing point for example, but if this is safe is not proven). From Buhlmann+GF it is said that it is 'safe' up to 100m, but a lot of divers use it successfull deeper. VPM-B+2 has shorter decotimes but more 'deepstops', and this was popular a few years ago and now more and more divers tend to skip the really deep deepstops. For me same, when I go to 100m, I don't do an 80m deepstop. My first stop of 1 minute is around 60m-66m. I do'nt plan myself with VPM-B. There is another theory about the difference of solubillity of nitrogen and helium. That can give you different decotimes too. But all it is a theoretically and mathematical approach and no absolute science.
The best advice if you want to do really deep/long decodives is learn to know your body. It does not give you any always safe information, but it can give you information what works for you. Why are some divers bent on a dive and others on the same dive not? No maths can tell you. No science can tell you. Otherwise no divers are bent anymore. We all know it never happens to us, but we don't know.

GF 90/90 and omitting the helium on a 10/70 mix to look like 10/0 works extremely well at reducing pesky deco.

 

[ajduplessis]

Helium ongases faster and offgases faster.

I agree that helium offgasses faster than the others gasses, but it's definitely not faster with ongassing. Both O2 and nitrogen ongasses a lot faster than helium.

 

[Kevrumbo]

The simple answer is that adding He to the mix will always give you less no-deco time than without He.

Not so sure about that one...

I agree that helium offgasses faster than the others gasses, but it's definitely not faster with ongassing. Both O2 and nitrogen ongasses a lot faster than helium.

From Bruce Wienke, Technical Diving in Depth, Reduced Gradient Bubble Model (RGBM) In Depth:

Helium NDLs are actually shorter than nitrogen for shallow exposures . . . Reasons for this stem from kinetic versus solubility properties of helium and nitrogen, and go away as exposures extend beyond 150 fsw, and times extend beyond 40 min or so.
Helium ingasses and outgasses 2.7 times faster than nitrogen, but nitrogen is 1.5 to 3.3 times more soluble in body aqueous and lipid tissue than helium. For short exposures (bounce and shallow), the faster diffusion rate of helium is more important in gas buildup than solubility, and shorter NDLs than nitrogen result. For long bottom times (deco and extended range), the lesser solubility of helium is a dominant factor in gas buildup, and helium outperforms nitrogen for staging. Thus, deep implies helium bottom and stage gas. Said another way, transient diving favors nitrogen while steady state diving favors helium as a breathing gas.
http://www.scubaboard.com/forums/ask-dr-decompression/32090-helium-offgassing-rate-2.html

Translating BRW's conceptual take on why shallow Helium has shorter NDL's than Air or Eanx 32 into practical and proper decompression profiles is not difficult: the NAUI RGBM Deco Tables have been out since 2003. Below (linked) are the comparative NDL's for Ean 32 and Helitrox; and example deco profiles for bottom times at 30m and 33m, for Ean 32 and Helitrox w/ & w/o O2 :
http://www.scubaboard.com/forums/te...358026-recreational-trimix-7.html#post5564996

The greater diffusivity of Helium over Nitrogen means it can potentially load free phase bubble seeds/bubble nuclei more readily than Nitrogen to produce a Boyle expansion pathology resulting in DCS upon ascent --even if you were diving trimix within air or nitrox NDL's. . .

---------- Post added October 8th, 2015 at 01:38 PM ----------

I agree, and from everything we have heard, she was very much "by the book" with regard to safety. My point being, that a momentary exposure to 1.6 ATM of oxygen or a quick bounce and ascent from 130 would not be expected to cause oxygen toxicity or (obviously) residual narcosis, but she was probably "not happy" about it either.

She likely had other compounding issues which did not make this "a momentary bounce" to MOD (all precipitated by Vertigo):

1) Vertigo -cannot orient or discern up from down; followed by 2) CO2 Retention & Narcosis, Dyspnea & Exertion Hypercapnia brought on by fighting the strong downcurrent; and then 3) final encroachment upon Eanx32 MOD/Ox-Tox limits in an uncontrolled descent.

This is a potential worst case scenario of an overwhelming set of cascading problems that will quickly incapacitate a lone buddy-separated diver: If victim cannot recover & stabilize in time from 1) and 2) above, resulting in stupor or loss of consciousness --then it is just a matter of a few minutes before final Ox-Tox Seizure in 3). . .

 

[Akimbo]

Recreational Trimix uses such small percentages of Helium that the arguments for and against are pretty marginal, IMHO. This extends to the effects on decompression as well as respiratory workloads. That is why commercial diving has never taken a serious interest in Trimix, especially now that surface based recycling systems (basically high powered rebreathers) are widely available. We use HeO2 instead.

The vast majority of recreational Trimix is used in that narrow band where it helps alleviate narcosis symptoms but can be safe and productive on air anyway. Granted, safety margins for surface supplied divers are much greater than for Scuba divers due to hardwire communications, essentially unlimited gas supplies, professional supervisors that can yank our butts off the bottom by pulling on the umbilical, and much greater experience and training levels.