MOD marking for 21/35

[rjack321]

AJ was your T1 fairly recent?

Cause 3 yrs ago there was no 150ft bottle marking and 30/30 now has an official MOD of 100ft (as recent class documents) have mentioned.

I just can't quite figure out when 21/35 was revised.

 

[jjones9527]

The thing is Tech 1 doesn't take into account the use of a stage bottle, so the only 21/35 you would have would be a back gas, and back gas uses the 1.2ATA/100ft END. Stage bottle marking seems to be changing based on the use of the gas, ie bottom gas or deco gas. I did Tech 1 in Aug, and how it worked for us was 32% to 100ft, 30/30 80-120ft, 21/35 100-150, 18/45 150-200, 15/55 200-250, 10/70 250-300. Now obviously we weren't doing anything deeper than 170, but thats the gas table we were given. If I'm going to be diving something deeper than 140 I will use the 18/45 so that I have the extra buffer. I know people who don't mind pushing 21/35 to 160-165, but its not for me. If I think there is a chance of breaking 150 I'll dive 18/45. The marking of stage bottles seems to be fairly recent, and would only be covered in a Tech 2 I imagine, as thats where use of a stage bottle is taught. All the Tech 2 guys I dive with learned to use 190 for 21/35 and 240 for 18/45.

 

[rjack321]

hmmm 30/30 was still to 120ft as of last August? But 21/35 was only to 150ft eh? I certainly agree with you about using 18/45 in the 165ft range.

Looking back on the powerpoint used in my Tech1 the usage depth range shown for 21/35 is 120-160ft and the MOD shown is 187ft. For 30/30 the usage range is 80-120 and the MOD is shown as 120. The date on that powerpoint (no copyright shown) is 3/28/2005 but that seems to be the date they were saved to a CD for me. Not the date they were created presumably by AG.

The more recent Tech1 powerpoint created by Richard Lundgren with a 2006 copyright has a table. The heading is "MOD Feet" and it shows 0-100 for 30/30 and 0-150 for 21/35.

So somewhere between early 2005 and 2006 the guidelines for 21/35 seemed to shift from MOD 190 to MOD 150. And likewise 30/30 got officially revised to 100ft but at least in your class its still a 120ft gas like it was for mine.

Despite GUE's superb consistency in many arenas, for these two gasses the "latest and greatest" recommendations are a bit hazy.

 

[Bismark]

I believe there is a new powerpoint as of last October. I saw it and Dan said it was the newest version (at least that is how I remember it). PPo2 of 1.2 is the new black.............

 

[jjones9527]

As I was doing Tech 1 Richard, Dan and JJ were updating the slides via email almost daily, and we were helping edit, so we had the most up to date info. I just looked at the Tech 1 work book we were given which was still being worked on but has 2006 as the copy right on the bottom. The table in it has the MOD for 30/30 as 100, so perhaps I'm mistaking the 120 for what were told on DIRF.

 

[rjack321]

I believe there is a new powerpoint as of last October. I saw it and Dan said it was the newest version (at least that is how I remember it). PPo2 of 1.2 is the new black.............

Yeah its seems to have shifted from "use it in this range but mark it deeper cause you could breath it deeper if you had to"
to
marked MOD is 1.2

I'm using them roughly in the recommended zone anyway. Just trying to make my marking consistent with the herd :d

 

[PfcAJ]

rjack, my class was over the summer, so a good 6 months or so. The course really focused on 21/35 with 50%. The other gasses were touched on, but not in detail like 21/35.

Ok, this is taken DIRECTLY from my T1 powerpoint dated for 2007, slide 67.

32% - 1-100
30/30 80-120
21/35 - 120-160

Thats pretty much corresponds to the MOD markings I listed earlier.

 

[LG Diver]

From my Fundies course PPT taken June 2007 (copyright 2007 material)


Depth (Feet) -------------- Mixture (02/He)
0 – 100 ------------------- Nitrox 32 or Triox 30/30
101 – 150 ----------------- Trimix 21/35
151 – 200 ----------------- 18/45
201 – 250 ----------------- 15/55
251 – 300 ----------------- 10/70
300 + -------------------- Appropriate O2/Helium (Heliox)

 

[rjack321]

rjack, my class was over the summer, so a good 6 months or so. The course really focused on 21/35 with 50%. The other gasses were touched on, but not in detail like 21/35.

Ok, this is taken DIRECTLY from my T1 powerpoint dated for 2007, slide 67.

32% - 1-100
30/30 80-120
21/35 - 120-160

Thats pretty much corresponds to the MOD markings I listed earlier.

Yeah those are the I was taught, although I know someone sent me a set of 2006 slides (I forgot who) that shows 100-150 for 21/35. And 80 to 100 for 30/30. Those slides are at work so I'll have to dig them up tomorrow. Seems to be inconsistent which is what I felt it was when I started this thread. It sprung forth from the similar discussion over on DIRx

It doesn't really matter THAT much to me.

Its just that I have several bottom stages which I use to get 2x T1 dives in a day. I keep changing the markings for various gases... but if I put 21/35 in them, I want to mark them consistent with what out of town guests find "normal" and "official". Clearly 170 would be a disaster waiting to happen. But 150, 160 and 190 are all potentially viable depending on when people were taught, their experience, and their expected use.

When used for a second recreational dive on 32% everyone seems fine with them being marked "100". I don't use 30/30 more than once in a blue moon, so whether that would be marked 100 or 120 isn't very relevant for me personally.

 

[limeyx]

That has always been my thinking too, but the 120 label still confuses me because it could be 32%, 30/30, or 35/25...

but the kind of dive you do will dis-ambiguate this one.
you wont deco on 35/25 for a 32% or 30/30 dive.
35/25 is probably going to be a 220ft+ dive.


I would mark gases at 1.4 (21/35 = 190) but still obey the "average" 1.2 PPo2 for the bottom portion (and actually 1.2 average for deco except for O2 segments)