Gas choice for 100' deco dives

[StreetDoctor]

We're thinking about doing some 60 min. 100' T1 dives in the near future, using 32% for back gas are you guys using 100% instead of 50% for your deco gas or still using 50%? We didn't talk about the use of 100% a lot in my T1 class, or at least I don't remember it :mooner:

 

[Rhone Man]

I suspect you will get an array of opinions, but if I was planning to dive that profile I would try and deco on something quite a bit richer than 50%. Jumping from your back gas of 32% to a deco gas of 50% doesn't give you that great a benefit. I would try and shoot for minimum of 75%.

According to my deco software (HLPlanner), 60 minutes at 100 feet on EANx32, you would not hit your first deco stop until 30 feet anyhow. So on that software your 'leanest' sensible mix would be around 80%. I suspect your most efficient mix would be 100%, and just do your 30' stop on back gas.

 

[LiteHedded]

I use 100% on those dives

 

[StreetDoctor]

Makes sense, we were on a recent dive where divers did a 2nd dive to 100' and only brought a 50% bottle while 100% was available. Just wondering what everyone's opinions were.

 

[Blackwood]

I too use Oxygen.

As Rhone noted, going to 50% from 32% is pretty irrelevant (especially at less than 1ATM pressure drop). 80 feet isn't that far to go on backgas, so gas reserves aren't really pushing me to use a deeper bottle.

 

[Rainer]

100%.

GUE does a piss poor job teaching deco on this gas. Play with software till you feel comfortable with it (there are some "on-the-fly rules" you'll be able to deduce). Don't forget that min gas must still cover the intermediate back gas deco on the way to the switch at 20'.

These longer dives in shallower water are a lot of fun.

 

[netmage]

We're thinking about doing some 60 min. 100' T1 dives in the near future, using 32% for back gas are you guys using 100% instead of 50% for your deco gas or still using 50%? We didn't talk about the use of 100% a lot in my T1 class, or at least I don't remember it :mooner:

In Lake Michigan - I'd make a strong case for 100%... That thermocline can be a bitch... The better boats made a practice of dropping O2 from the bow,...

 

[ucfdiver]

I use 100% on those dives. Even on 2 hour dives around 85-100ft, rock bottom gas reserves stay manageable.

 

[deepstops]

Another vote for O2 for this dive.

 

[SuPrBuGmAn]

O2 for me.