Deco gases

[JohnD]

<font color='#F52887'>what are the standard GUE/DIR deco gases? I have Decoweenie and there is an option to use DIR standard gases for deco, so what are they?

[Mark Chase]

100% &nbsp; &nbsp;6m

50% &nbsp; &nbsp; &nbsp;21m

35/25 &nbsp; &nbsp;36m

21/35 &nbsp; &nbsp;57m

Strangly thats as deep as they go

ATB

Mark Chase

[Bob Cooper]

There are standard bottom mixes and standard deco mixes.

Bottom mixes go like this:
&lt;30m 32% or 30/30
&lt;45m 21/35
&lt;60m 18/45
&lt;75m 15/55
&lt;121m 10/70

Deco mixes go like this:
&lt;6m 100%
&lt;21m 50%
&lt;36m 35/25
&lt;57m 21/35

I may be a little out of date with the deep gasses (these things change).

I think Decoweenie allows you to customise your gasses? (like DPlan)

Bob

[JohnD]

Originally Posted by [b

Quote[/b] (Bob Cooper @ Dec. 23 2003,20:18)]I think Decoweenie allows you to customise your gasses? (like DPlan)

Bob

<font color='#F52887'>It does, but I was just wondering what the &quot;standard&quot; ones are. does that mean that any deco stops 36m or deeper use He in the mix?

[Bob Cooper]

Originally Posted by [b

Quote[/b] (JohnDuncan @ Dec. 23 2003,20:43)]

Originally Posted by [b

Quote[/b] ]does that mean that any deco stops 36m or deeper use He in the mix?

No, not necessarily. &nbsp;You need to consider the advantages of using the gas against the disadvantage of carrying it.
Obviously, a 60m dive may require a stop deeper than 36m but that does not mean you need to carry a 36m deco bottle, that could mean 3 bottles for a 60m dive. &nbsp;For that sort of dive you would do your deep stops on backgas (18/45) and use 50% from 21m. &nbsp;You might also want to use O2 at 6m but, again the advantage of using the gas might be marginal compared to the disadvantage of carrying it in the first place.

It's swings and roundabouts.

For the sort of diving we are doing, 2 deco gasses is usually the max we would consider, although we are planning some deeper stuff next year which will involve 3 deco gasses. &nbsp;In this case the 36m bottle will have helium in it. &nbsp;This is new territory for me, but presents an exciting challenge.

Bob

[JohnD]

<font color='#F52887'>you are right about the disadvantages of carrying the cylinders againsnt the advantage the different mix for deco might give you. When I plan my dives, I do the plans for no deco mix and for losing EITHER of my deco mixes and sometimes the difference is quite marked on deco stop times but other times the saving isnt worth the extra hassle.

[Digger]

<font color='#000080'>At 36m doing deco, couldn't you use nitrox and be done with it? I'm a bit confused as to why you'd cut it with helium. Is it to reduce the narcotic effect, or because He is a faster gas?

I don't really understand, so talk to me really slowly. The thought of decoing at 36m is well beyond my scope, but I just want to understand!

[Mark Chase]

Originally Posted by [b

Quote[/b] (JohnDuncan @ Dec. 23 2003,21:55)]you are right about the disadvantages of carrying the cylinders againsnt the advantage the different mix for deco might give you. When I plan my dives, I do the plans for no deco mix and for losing EITHER of my deco mixes and sometimes the difference is quite marked on deco stop times but other times the saving isnt worth the extra hassle.

Yes but that isnt going to last. Once you start past 60m the number start to rack up big time. It is almost imposable to carry enough travel gass to compleat the deco on a deep dive. As an example a 40min dive to 65m on DIR 15/55 SAC for deco 15lpm would require a 18ltr travel gas to compleet the deco on a 30/85 profile using 50%. Using 35/25 as a deco mix you would need a 20ltr tank blown to 345bar

If you are hardcore DIR you can ignore the helium in the deco mix and get the time down to a 15ltr

Your not going to carry two 15ltr stages are you?

In realiaty past 60m you need to be looking at drop tanks for bail out or very short bottom times. I did two 65m dives with 35 &amp; 40min bottom times this year and used two 10ltr stages blown to 250 bar.

Some divers do do these dives on 7's but they have to do 20min max bottom times to make it work. To me thats just not acceptable in terms of invested cash and effort to do the dive.

Past 70m I would be seriously looking at three deco gas mix.

Or a CCR

ATB

Mark Chase

[Bob Cooper]

Originally Posted by [b

Quote[/b] (Digger @ Dec. 24 2003,14:37)]

Yes, one of the reasons for using helium at 36m is the reduced narcotic effect and because it is a &quot;faster&quot; gas. &nbsp;Other reasons include the reduced breathing effort due to reduced gas density leading to reduced CO2 retention. &nbsp;Reducing breathing effort and CO2 retention are thought to reduce susceptibilty to Oxygen toxicity too.

Just using 35% nitrox at 36m would be of little benefit.

[Bob Cooper]

Mark

I only saw your reply after posting mine......

40mins at 65m is too long for an ocean dive. &nbsp;The run time would be around 2 hours. &nbsp;As you know this is a little too long for us, and the bottom gas reserves are a little marginal with 2x15L and dangerously marginal with 2x12L. &nbsp;I'll be doing some more of this sort of diving next year and I've just invested in a pair of 15's.

Keeping the bottom time to &lt;30mins at 65m would give ample reserves of deco gas. &nbsp;And we still have the drop bottle of 100% to fall back on if we loose that for some reason.

Happy Xmas!

Bob