Nitrox with my 80 tank...too small??

[Scuba-Quebec]

I would like to switch on Nitrox soon...I was wondering if my 80cu. steel tank or going to be enough for an extended bottom time??....I was thinking maybe going with E8-119 cu. Pressed Steel tank....

 

[Boogie711]

Probably - remember, it's not just you that has to surface on that thing, but it's also your distressed buddy in an Out-of-air emergency.

Anything over 90 feet or so, where Nitrox really starts to become valuable in extending bottom times, isn't going to leave you with enough gas to get the two of you to the surface quickly if you're pushing NDL's already.

 

[matt_unique]

I would like to switch on Nitrox soon...I was wondering if my 80cu. steel tank or going to be enough for an extended bottom time??....I was thinking maybe going with E8-119 cu. Pressed Steel tank....

If you have a low SAC rate an 80 with Nitrox would allow you to extend your NDL bottom time.

--Matt

 

[Spectre]

Even if it doesn't, you get the benefits of coming out 'cleaner' with nitrox then the same [or even equivalent] time on air.

 

[Dive-aholic]

It's not the size of the tank, it's the sac rate that matters. Calculate that and see if an 80 will get you the bottom time you're looking for. If not, what about a 95? Avoid going with more than you need. A bigger tank is nice underwater, but remember you still have to carry it to the water.

 

[msandler]

If you dive proper gas managment rules you will benefit from a larger tank. If not, well... SAC is not the factor you should base your decision on. It is inconsistent and wasn't part of your initial question.

 

[Kim]

If you dive proper gas managment rules you will benefit from a larger tank. If not, well... SAC is not the factor you should base your decision on. It is inconsistent and wasn't part of your initial question.

Out of interest, how do you calculate a dive profile using proper gas management rules if you aren't aware of your SAC?

 

[The Kraken]

By the volume in your tank.
Not getting into the different theories of gas management, but one school of thought uses "the rule of thirds" - 1/3 down, 1/3 on site, 1/3 back + reserve.

 

[Kim]

Yes I agree. That won't on it's own though give you any idea how long each 1/3 will last will it? The original poster seemed to want to know that.

 

[The Kraken]

No, it won't. You really need to know your SAC and the planned dive depth to do a computation.

Scuba-Quebec,
That's a difficult question to answer. It's a yes and no type of question.

Let's say that you're a pretty good diver and your SAC rate is .40.
Your diving gas mix is EAN32
Your MOD (maximum operation depth) is about 110 FSW based on a PO2 level of 1.4.
By the table your max bottom time would be 25 minutes.
Without splitting hairs, your gas consumption for that dive plus a safety stop of 3 minutes would be about 48 cubic feet of breathing gas.
In this case your 80 would be just fine.

Now let's take a dive of 50 FSW using the same SAC and gas mix.
Your max bottom time is 155 minutes + a 3 minute safety stop.
This dive would require about 156 cubic feet of breathing gas.
I think you'd come up a wee bit short.