DIR standard gases

[jtivat]

I did a few searches and came up with a few discrepancies. Can someone please give me a list of the DIR standard gases? I would like back gases with depth ranges and then deco gases. Also are there mandatory deco mixes for depth ranges? Meaning if I did a 270’ dive do I need three gases and they need to be XYand Z?

Thanks
JT

 

[rjack321]

I did a few searches and came up with a few discrepancies. Can someone please give me a list of the DIR standard gases? I would like back gases with depth ranges and then deco gases. Also are there mandatory deco mixes for depth ranges? Meaning if I did a 270’ dive do I need three gases and they need to be XYand Z?

Thanks
JT

Not quite sooo prescriptive as depth X = gas Y. But here you go...
Backgases:
0-100ft = 32%
80-120ft = 30/30 if you're GUE DIR
80-130ft = 25/25 if you're UTD DIR
100-160ft = 21/35
150-200ft = 18/45
200-250ft = 15/55
250+ = 10/70 for GUE
250-300ft = 12/60 for UTD
300ft+ = 10/70 for UTD

I took a few minor liberties with the above. The GUE depth ranges are slightly more conservative (for ppO2) for 30/30 and 21/35 than listed although many GUE divers still use the older recommendations. ppO2 for backgas is limited to about 1.2, END limited to 100ft. No deep nitrox, or hurry to get off trimix based backgas. More He is in general considered desirable.

Deco gases and range used:
o2 = 20ft
50% or 50/25 for big dives = 70 to surface or until O2
35/25 = 120 to 70
21/35 = 190 to 120

Except for "entry level" 150ftish deco dives done on just 50%, all deco gasses except O2 are used over 5 stops with a peak ppO2 of 1.6 and an average ppO2 of 1.2

 

[cfenton]

I recently took Tech II with Dan MacKay. Because I had done my Tech I before GUE changed the MOD markings from 1.4 to 1.2 this was something we talked about at length.

Bottom gases up to the Tech II level (PPO2 = 1.2):
- 32% ---> MOD 100
- 30/30 --> MOD 100
- 21/35 --> MOD 150
- 18/45 --> MOD 200
- 15/55 --> MOD 240

Deco gases (PPO2 = 1.6):
- 100% --> MOD 20
- 50% ---> MOD 70
- 35/25 --> MOD 120
- 21/35 --> MOD 190

The way it was explained to me was that GUE had always recommended a 1.2 average and that the only change was that the 1.4 "hard limit" had been removed. Meaning that you could still take the gas to 1.4 as long as you averaged 1.2.

He also told us not to go remarking all our bottles just yet.

 

[cfenton]

Also are there mandatory deco mixes for depth ranges? Meaning if I did a 270’ dive do I need three gases and they need to be XYand Z?

No. It's a matter of taking into consideration deco, lost gas, and min gas issues.

 

[rjack321]

The way it was explained to me was that GUE had always recommended a 1.2 average

me too

the only change was that the 1.4 "hard limit" had been removed.

Still has never made sense to me. 21/35 is not really trying to kill me at 155ft I would us it to 160ft without much concern. If you are doing a tech1 dive and dipping a bit below 150ft its fairly straightforward to average 1.2 And the new hard limit of 150 is <1.4

He also told us not to go remarking all our bottles just yet.

We have our own schema down here that seems to be fine. However they choose to mark things in High Springs is great and all, but we need our markings to make sense for our multi-day multi-dive trips.

 

[cfenton]

Still has never made sense to me. 21/35 is not really trying to kill me at 155ft I would us it to 160ft without much concern. If you are doing a tech1 dive and dipping a bit below 150ft its fairly straightforward to average 1.2 And the new hard limit of 150 is <1.4

My understanding is that 150' is not a hard limit - that it is okay to go to 160' as long as you average 150'. I think the logic for the change may have stemmed from many divers pushing the limits of a gas based on the label ("because it says 190' I will average 1.4")

We have our own schema down here that seems to be fine. However they choose to mark things in High Springs is great and all, but we need our markings to make sense for our multi-day multi-dive trips.

I hear you. If 150 isn't a MAXIMUM Operating Dept then why didn't we just keep our 21/35 bottles marked 190 and continue to average 1.2 at depth? Having two bottles for 21/35, one marked 150 and the other 190, doesn't really make things easier or safer in my opinion. But I digress...

 

[jtivat]

Thanks guys I want to plug these numbers into the deeper dives I do and see what the profiles look like. Is there a depth or time limit that three deco gases are required or is that up to each diver?

JT

 

[jtivat]

Sorry forgot one other question, is there a standard in DIR for air breaks?

 

[rjack321]

Sorry forgot one other question, is there a standard in DIR for air breaks?

GUE does 12 on 6 off
UTD does 10 on 5 off

Just to be different I suppose, neither are scientifically validated. Both agencies point to studies showing decreased pulmonary function at starting around 18 to 20 mins on 1.6 ppO2. Most divers count the break time as O2 time, some don't but I suspect that's rarer.

As far as 3 gases goes that depends on OW vs. cave, total exposure etc. I guess you'd say the line there is somewhat discretionary and typically in the 220-240ft or even a little more neighborhood. Most divers end up needing a bottom stage before they add a 3rd deco gas although that's not a firm rule.

 

[rjack321]

My understanding is that 150' is not a hard limit - that it is okay to go to 160' as long as you average 150'. I think the logic for the change may have stemmed from many divers pushing the limits of a gas based on the label ("because it says 190' I will average 1.4")

I hear you. If 150 isn't a MAXIMUM Operating Dept then why didn't we just keep our 21/35 bottles marked 190 and continue to average 1.2 at depth? Having two bottles for 21/35, one marked 150 and the other 190, doesn't really make things easier or safer in my opinion. But I digress...

Hah no wonder I've been confused

We sometimes bring 21/35 stages to stretch a set of doubles to 2 or 3 dives (since we often have to bring all our gas with us and have guests using some doubles etc). 190 seems "sooo deep" but we don't get them mixed up with other bottles on the boat and we don't use them below about 150-160 so it seems to work for us.