MOD marking for 21/35

[PfcAJ]

How about a cave dive where you dive 30/30 on the bottom for a while, then dip down to 150 for a while. Now you decide you want a 120 foot deco bottle.

The 30/30 and 35/25 may both be marked 120 -- which one do you choose for the deco ? will it make a huge difference? in this case likely not as the mixes are (as you might expect) very similar.

You could also just take 21/35 as a bottom gas and do more deco .. I think the EKPP is dealing with exactly this issue (at deeper depths)

Why would you want a 120 deco bottle for a 150ft dive...that makes no sense.

I stand corrected on the current MOD's for gasses. I went through my C1 course materials (more recent then my T1 stuff), and the MOD for 30/30 has been reduced to 100ft.

So this is pretty much the standard:

Bottom
32% 100
30/30 100
21/35 150
18/45 190

Deco
100% 20
50% 70
35/25 120
21/35 190

 

[jjones9527]

And I've got 18/45 to 200'!? Some real discrepancies coming out now. Might be time for an email to Quest.

 

[limeyx]

Why would you want a 120 deco bottle for a 150ft dive...that makes no sense.

I stand corrected on the current MOD's for gasses. I went through my C1 course materials (more recent then my T1 stuff), and the MOD for 30/30 has been reduced to 100ft.

So this is pretty much the standard:

Bottom
32% 100
30/30 100
21/35 150
18/45 190

Deco
100% 20
50% 70
35/25 120
21/35 190

true enough. I was trying to postulate a situation where you might have 30/30 and 35/25 on a dive and messed it up.

I dont have a problem with the above MOD's, or GUE changing MOD's

BUT

1) They need to tell people that have already passed the classes so we dont look like morons
2) You now mark 21/35 and 18/45 etc. differently if they are used as a bottom stage or a deco bottle -- but its the same gas. Does that make any sense ?

 

[limeyx]

See you and I were trained the same way "1.2 average". But recent tox fatalities and the rather hazy guidelines are backing off to a hard MOD of 1.2 for the working phase.

I guess I wouldn't be in such a quagmire if I didn't feel diving 21/35 to 160ft was relatively safe. Marking it 190 is rather too generous on END and marking it 150 is a bit excessively conservative on ppO2.

170 would be fine with me except that there's too great a risk of screwing it up with a 70 bottle.

And the last choice...
I'd happily leave them unmarked except I have a variety of stages kicking around and I'd hate to grab the wrong one and discover it at a dive site when the analyzer told me of my error. Or to have a 21/35 and a 32% stage in the boat for a multidive trip and have the tape come off.

Mostly though this seems to be a remarkably unstandardized chunk of DIR which could benefit from some learn-ed discourse.

All good points my friend. I dont see a problem labeling 21/35 as 190 (for ex.) and 30/30 as 120, but then planning the dive to a max of 160 on 21/35 (depending on conditions, maybe shallower than that) but by marking it 190 I know if I absolutely have to, it's "safe" (from a Tox perspective) to shove that reg in my mouth at 190 if I have to.

In general, for a given dive, we are going to know if we are bringing a 190 deco gas etc. ( I would hope

 

[PfcAJ]

Is it really safe to "shove" a high ppo2 gas in your mouth at nearly 200ft? I don't know about you, but I don't switch gasses unti I am completely ready and my buddy is watching me.

 

[rjack321]

All good points my friend. I dont see a problem labeling 21/35 as 190 (for ex.) and 30/30 as 120, but then planning the dive to a max of 160 on 21/35 (depending on conditions, maybe shallower than that) but by marking it 190 I know if I absolutely have to, it's "safe" (from a Tox perspective) to shove that reg in my mouth at 190 if I have to.

In general, for a given dive, we are going to know if we are bringing a 190 deco gas etc. ( I would hope

Ok the old 190 and 120 it is. Seems like this is not the way the recent MOD revisions have quietly suggested, but so be it.

In reality you ain't switching to a bottom stage anywhere except on the surface. So really these are labels to be able to do final surface and/or gear loading checks. Or to be able to say to the crew, pass me the rigged bottle with "RJ" initials and marked "190". They aren't something you even need to read UW.

 

[jjones9527]

In reality you ain't switching to a bottom stage anywhere except on the surface.

Well not necessarily. We often have 3 stages of 32% and/or 30/30 (all labeled 120) for some of our dives. In this case we only have 1 deco gas (O2). The dives are 2-3hrs scootering in the 60-100ft range. We hang 2 32% bottles on the front, and a 30/30 and O2 on a leash. The 30/30 is basically there to lighten the load while still giving us a breathable gas if we need it.

There should never be a case where you can confuse a bottom stage with a deco gas.

Again I can see both sides of the fence. For a bottom stage you don't want to be "working" past the 1.2 MOD, even if it is "safe" to breathe past that. So looking over and seeing someone breathing a 150 MOD at 160 would raise some alarms. Personally planning the dive and sticking to the parameters should negate any need for multiple labeling schemes. Slap the 1.6 (or 1.4 for deep gas) MOD on the bottle and dive it within your plan. We don't label back gas we plan it for our max depth. Bottom stages are labeled for gas switching, but should contain the same as back gas. If you break your max depth because of an emergency you're out of gas options anyway, regardless of what you are carrying or how it is labeled, as you are breathing your deepest gas already.

 

[MattL]

Im thinking with the new mod with 30/30 being a 100 ft.
as for the 21/35 I Know that if mod stages says 190 and im useing it as a bottom gas i know not to take it past 150.

 

[MattL]

so Halcyon makes mod for 20,70,100,120,150,190,200,240,250 and 300
so the 150 would be bottom gas for 21/35 and 200 would be for 18/45 or for me tape and a maker becouse i cant pay for to al80s for bottom stages

 

[rjack321]

Well not necessarily. We often have 3 stages of 32% and/or 30/30 (all labeled 120) for some of our dives. In this case we only have 1 deco gas (O2). The dives are 2-3hrs scootering in the 60-100ft range. We hang 2 32% bottles on the front, and a 30/30 and O2 on a leash. The 30/30 is basically there to lighten the load while still giving us a breathable gas if we need it.

There should never be a case where you can confuse a bottom stage with a deco gas.

Again I can see both sides of the fence. For a bottom stage you don't want to be "working" past the 1.2 MOD, even if it is "safe" to breathe past that. So looking over and seeing someone breathing a 150 MOD at 160 would raise some alarms. Personally planning the dive and sticking to the parameters should negate any need for multiple labeling schemes. Slap the 1.6 (or 1.4 for deep gas) MOD on the bottle and dive it within your plan. We don't label back gas we plan it for our max depth. Bottom stages are labeled for gas switching, but should contain the same as back gas. If you break your max depth because of an emergency you're out of gas options anyway, regardless of what you are carrying or how it is labeled, as you are breathing your deepest gas already.

In your case you are basically doing cave dives not OW dives. As Nawindy mentioned earlier 1 stage gets you into the 300ft range.

In my case (here on the West Coast) we use a stage of 21/35 to get 2x T1 dives off one set of doubles, or to have 32% for a second recreational dive while using the backgas in doubles for rockbottom. Once Limeyx and I used 30/30 in a stage for a second square profile recreational dive at 100ft in crummy vis with backgas as rock bottom.

I would never mark a stage of 32% as 120. And I certainly wouldn't have it mixed up with a bunch of 30/30 stages on the same dive/leash. Nope. That is way too deep for that gas both END and ppO2. Sure you have a hard bottom of 100ft, but you should not rely on a hard bottom to make your gases safe to breathe IMO.