How 'bout a decompression theory thread? (OC Deco gases with helium)

[Corndogg]

Alright, so I usually do 200ft OC dives on 18/45 with 20 to 30 minute bottom times then ride an explorer up using 36 and 80, sometimes 100 if the boat has it.  I'm working my way deeper and have been told I need to start using helium in my deco mixes.  Sounds good, just wanted to start a huge thread and see what everybody else is doing and why. This means you divbum    Readyyyyy............GO! 

[divbum]

You had my attention all last week, and now you want me to type a thesis?!?!?

[divbum]

Have you ever felt anything at your deep gas switch???  Narcoisis or just anything?

[Corndogg]

Yeah sorry, I wasn't really in dive mode when I came out there but after making some of the best dives I've ever done I got kinda revved up.  Started thinking I might be doin a lot more deep diving this season.  I get bored unless challenged or learning.  I've been to 234 on the Kamloops and am told I can get 270 so I'm gonna do that in a few weeks.  I've heard you say you use helium in your deco mixes.  I want to learn the theory and why I should be using it.  Any info and resources would be appreciated.  And no I almost always use 36 and usually dont get any narcosis when I switch over although I do get narced easily prolly from lack of confidence(experience).  I've never felt the slightest hint of DCS, no pain or discomfort.  If anything I feel better after a good mix dive.  Of course I am totally buff. >

[divbum]

What is your plan for 270' gases - bailout tables ( i know you use the HS) but I need to see values of total pressures.
That will help me get started.  I might not get into this until Monday or Tuesday.

[Vtach]

Primary reasons, not necessarily in order of importance depending on the dive:

1.  Ease the transition between backgas and deco gas.  Gradually lower the pHe so I'm not risking any possibility of inner ear DCS.
2.  Take advantage of deepstops and still use a 1.6 pO2 without adding a significant amount of nitrogen in the deco gas.
3.  Reduce narcosis on deco.
4. More practice at blending and spending quality time watching gauges while drinking the beverage of my choice. ;D

[divbum]

Condogg,
I am waiting for your dive plan...
But Todd has really hit the key points, biggest one being inner ear DCS.

I personally won't dive deeper then 200 without He in my deco mix(s).

[Corndogg]

Had to get the wreck list/plan.  Looks like this is what we're gonna do:

Fri 3PM  240 for 20 Kamloops,  15-85
Sat 9AM 270 for 25 Kamloops, 15-85
Sat 3 PM 160 for 25 Emperor
Sun 9 AM 200 for 25 Congden Stern
Sun 3 PM 250 for 25 Kamloops
Mon 9 AM 150 for 20 Chisholm Engine

I have two sets of doubles.  Last year we brought up 15-85 and blew em down.  I can get another set of doubles and bring 80 stages.  On Ken's boat he's got air, surface supplied O2, can bag and continuous blend.  I've been reading on the deco stop, alot of those guys breathe helium mixes but don't tell the computers/planners.  I'm told the exploder doesn't tax you as bad for staying on He.  I'm thinking of carrying an 80 of bottom mix and an 80 of deco, maybe 36 with some He.  Let me know what you think.  Thanks Greg ;D

[Corndogg]

Also, would it be bad to run air in a drysuit doing deep heliox dives.  Whats the whole story with that?  Happy Typing

[divbum]

I will dig you up some articles in the next week.  I am out of town tomorrow for 4 days.  The likely hood of skin bends is removed/reduced by using argon.
Not sure what V-planner gives you as a ball park but as a refernce I would do something close to this for the 240 for 20 dive
I would discount half my decent time buying an extra 2minutes on the bottom
so 15/85 for 22ish
Start making short stops from 180 - 130
120 switch 35/25 for 3
110 -2
100-2
90-2
80-2
70-2
60-2
50-3
40-3
30-5
20 - on 02- 8 off for 3 on for 8
3-5 minute ascent
Should be a low 70minute runtime

Without argon and no He at 120 you have a huge Phe and Pn2 diferential of on and off gasing.  You will likely feel signed of narcosis and dizziness from gas tissues in your inner ear, and the instant Total pressure of the gases without HE.  I have to dig, but will get some stuff to you via email.

The above table is not recomended and may lead to DCS for anyone attempting to use it with or without a full understanding of the varibles it is set around.  You cannot learn to dive on the net...

What do you figure you gas will be for Sunday?