How long does a tank of air last

[Kim]

Kim, I have found that with warm water, ..............

Are you sure that answer is meant for me?

It's true though.....as I said - things get better with practice! Of course I'll never get to the same consumption as my diminutive Japanese wife! It's one of the many things that ladies are generally a whole lot better at!

 

[JacobK]

Being very new to this and a bit wet behind the ears.

Until your gauge reads 0...

Like everybody has said, depends on many factors.

On my first dive on a steel 80 at 2900 PSI in 15 ft of water, I got down to 500 PSI in 29 minutes.

On my last dive (dive number 7 of my diving career), on a AL 80 at 3000 PSI, with a max depth of 40 feet, I got down to 500 PSI in 31 minutes.

Do not worry about it in the beginning. Just keep diving and watch your gauge. As you dive, you will end up beginning under water longer. Breathe calmly, relax and enjoy the sights!

 

[FOUNDATIONER]

aONE, aTWO, aTHREE......Three...no wait, thats a tootsie roll pop :06:

 

[kidspot]

btw - just in case you meant "how long can you store a tank of air" most would say that after 6 months to a year the air could go "stale" ... just so many interpretations of that little phrase

Back to what everyone else is saying ... I took a group of new divers out (2nd open water dive for them) when I had about 20 dives and we aborted the dive at 18ft with less than 15 minutes... one of the guys was already down to 500psi ... On the other hand last Sunday a friend and I hit the water with the same tanks (AL80's) and got 102 minutes with an average depth of 21ft... so it can vary a LOT - and I seem to remember on Uncle Pugs last Maui trip he had a 180 minute dive on a single AL80 ... But then again I don't think he actually breathes, it just slowly leaked from his tank

Aloha, Tim

 

[Spectre]

(The amount of gas in cubic feet) divided by ((your average depth in ATA) times (your surface air consumption rate in cubic feet per minute))

So an aluminum 80 filled to 3000 psi is 77.4 cubic feet. On a dive to 60 feet [assume square profile for kicks].

Assuming a SAC of .8

First the safety stop: 15 ft = 1.45 ATA. 3 minutes. .8 SAC. That's 3.5 cuft

77.4 - 3.5 = 73.9 cuft remaining.

Assume a 30 ft/min ascent from 60 feet. That's an average of 30 feet over 2 minutes:

30 ft = 1.91 ATA. 2 minutes, .8 = 1.91 * 2 * .8 = 3.05 cuft

73.9 - 3.05 = 70.85.

60 ft = 2.82 ATA. 2.82 * x * .8 = 70.85 cuft. so 70.85 / (2.82*.8) = x = 31 minutes

Now if you want to plan for 500 cuft in reserve:

500/3000 = .167 .167 * 77.4 cuft = 12.9 cuft reserve.

70.85 cuft - 12.9 cuft = 57.95 cuft

57.95 / (2.82 * .8) = 25 minutes.


Now how you figure out your SAC rate is based on data from previous dives.

Record your starting and ending pressure for each dive. Get your time and average depth from your computer.

Let's go with 3000 psi starting, 750 psi ending, aluminum 80, 45 feet average depth for 50 minutes.

3000- 750 = 2250
2250 / 3000 = 75% of tank
.75 * 77.4 = 58.05 cuft

(45 ft + 33) / 33 = 2.36 ATA
58.05 cuft / (2.36 * 50 minutes) = .49 cuft/minute at 1 ATA

If you record your time and pressure when you begin your ascent, and get your average depth for your ascent and your average depth for your dive minus ascent, you can start collecting "work" consumption rates and "resting" consumption rates to allow for more complex and more accurate dive planning.

 

[Blackwood]

Now how you figure out your SAC rate is based on data from previous dives.

Record your starting and ending pressure for each dive. Get your time and average depth from your computer.

Or just breathe off a tank on the surface for one minute, monitor the change in pressure, and do the math.

 

[Wayward Son]

Do you mean how long does it last in use, or sitting in your garage?

 

[Spectre]

edit. eh, nevermind. just too stupid to bother responding.

 

[kidspot]

Or just breathe off a tank on the surface for one minute, monitor the change in pressure, and do the math.

In theory yes, but remember that the way you breathe and react sitting at the surface in a lawn chair may be vastly different than how you normally breathe while finning (or even hovering) over a reef. And 10 minutes is probably more necessary to see much significant change (in the way of data) on your spg. My last dive I timed at 5 minute intervals and was fairly consistently using 125psi every 5 minutes (average depth 21 ft) so I figured I would have enough air for close to 100 minutes with a 500psi reserve ... ended up being 102 minute dive surfacing with 400 psi (only about 6-8ft depth for the last 200 psi, so we were not overly concerned with dropping below 500).

Aloha, Tim

 

[JRScuba]

Wow that is an easy one. Until it's empty. LOL