Mt. Everest of Diving

[Stone]

Bennett took the technique one stage further by back-switching to pure helium for periods during decompression at the top stops, and is convinced that this was the single most important aspect of developing a safe deep-dive decompression routine.

Is this an accurate statement?

 

[AquaTec]

Originally posted by Stone


Is this an accurate statement?

I beleive the method he was using here is known as toggling

so while decoing on 100% O2 you do what is called back-switching to your trimix that will still provide adiquite O2 for the five minute breaks at the depth your at

but also durring the deco process there is another technique called toggling. this is were you go from a high PO2 / PN2 to a very low or zero PO2 / PN2 this can be done at any depth dependent on your PO2 / PN2 so by using pure He it would seem that he could perform this at any depth and not concern himself with PO2 / PN2 and still achive the desired toggling effect of off gassing.

there is a good link somewere on the toggling techniques and there advantages. I don't understand it to well myself except that deep divers are starting to do both toggling and back-switching.
back-switching is designed for when you are decoing on 100% and require an air break, well instead of the high PN2 of air switch to back gas [as long as PO2 allows] which will keep PN2 low and reduce your CNS clock better than the air break

ask Lost Yooper I will bet he has a link on the subject, he has them all

 

[Stone]

The "pure helium" makes me pause. . .

. . . Does this mean the diver takes a look at his timer and breathes "pure helium" for 30, 45, or 60 seconds?

 

[Bottom Feeder]

Originally posted by Stone


Is this an accurate statement?

Without wanting to stick my oar in where it does not concern me..............

Details have emerged of the 254m open-water dive in the Philippines in which 41-year-old Briton John Bennett set a world record depth. The dive beat by a large margin the previous record of 202.5m, set in March by Belgian Ben Reymenants at Dahab in Egypt.
Backed by a team from Capt'n Gregg's dive centre at Puerto Galera, Oriental Mindoro, Bennett dived on open-circuit trimix to a carefully planned schedule aimed at providing new parameters for deep diving in general.
Using a custom-prepared dive profile on Abyss software, Bennett employed very slow ascents and, during decompression, a relatively new technique called back-switching, in which the diver regularly switches from pure oxygen to the leanest oxygen mix allowed at that depth, to limit potentially dangerous exposure to high levels of oxygen.
Bennett took the technique one stage further by back-switching to pure helium for periods during decompression at the top stops, and is convinced that this was the single most important aspect of developing a safe deep-dive decompression routine. He reported no problems with decompression illness, oxygen hits or HPNS (a nervous system complaint linked with rapid descents to depth).
Bennett used four trimixes: 16/48 on the descent to 90m; 4/80 bottom mix from 90m down and back up to 150m; 10/69 from 150m to 90m; 16/48 again to 60m; and 23/23 to 39m. From here he used nitrox mixes of 33 per cent to 21m, 50 per cent to 12m and 73 per cent to 6m, from where he finished decompression on pure oxygen. Switchovers were extended over a period of time to ensure that his body did not react to a rapid change of gas.
Bennett's descent rate was 25m per minute, the ascent 25m/min to 180m, 15m/min to 150m, then 10m/min. He did 30-second stops every 10m from 150m to 120m, then one-minute stops from there to the surface.
For the dive a weighted line was set and PADI course director Alan Nash, an independent observer, witnessed Bennett return to the surface with a tag that had been set at 250m. After analysis of the dive computers and allowing for some line stretch, the depth of 254m was agreed.


Have I just posted the same thing as earlier (Sorry it's rather early over her, not awake yet)

 

[AquaTec]

Originally posted by Stone
The "pure helium" makes me pause. . .

. . . Does this mean the diver takes a look at his timer and breathes "pure helium" for 30, 45, or 60 seconds?

I don't know I am only guessing based on what I know of the theory behind it.

I would suspect that by using pure helium he could toggle it at any depth if he does a deco stop at 450ft he can switch to pure He for a few seconds and at 20 ft he can do the same.
this is lagisticaly simpler.

I could be talking out of my a** here but its just a theory

 

[AquaTec]

To me John's accomplishment and others that are right there on his tail is the same as walking on the moon.

Keep in mind there are something like a 1000 people a year that summit Everest. and there is a five year waiting list for your turn.

so with that in mind you are probable still comparable to the Doria.

For first ascents on mountain tops I would say the Britania, or Lusitania.

 

[Lost Yooper]

Toggling back and forth (air breaks) from deco gasses (especially O2) to your "leanest" O2 mix (ie, back mix) isn't unusual or all that new. Irvine has talked about it for quite some time. This toggling effect allows for the most efficient offgassing throughout the deco process by preventing pulmonary toxicity and vasoconstriction from occuring (the damage done to the lungs by long exposures to high PPO2).

There's been a few studies proving the value of breaks by Clark and Lambersten and by Youngblood and Nakano in Hawaii. I have various notes on all this, so if anyone is interested, they can send me a PM.

I have never heard of anyone using pure helium for deco though. I want more info on this if it's true, because I don't see how it's going to do a whole lot of good with the limited time you can stay on pure helium. It takes the body about 2mins to circulate all this stuff, so I'm pretty skeptical. Is there an official link or source that I could reference all this pure helium deco thing?

Mike

 

[ericfine50]

Maybe its Heliox. No N2 - probally one of the best deco gases to use. I think Bill Mee and JJ use it for th majority of their deco gases.

Eric

 

[Waterlover]

Pure HE will asphyxiate(sp) you almost immediately. No recovery.your done. you must have some O2 in there. If he breathed pure HE it would be another record setting event I think.
Ken

 

[Stone]

Pure helium wouldn't asphyxiate you right away. The danger with breathing an inert gas (vice holding your breath) is that there is no CO2 build up so you don't get the "must breathe" signal. There have been people who have been asphyxiated while purging large fuel tanks (i.e., big enough to walk in) with N2 because they felt like they were breathing normally, but there was not enough O2 to sustain consciousness (or life). Someone who has been on 100% O2 could probably breathe pure helium for a couple of minutes without a problem.