How much air should I aim to end with?

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robandliza

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Hi

Question from a new diver

As a basic rule of thumb, is there a certain amount of air I should always aim to have left in the tank at the end of a dive, and if so, how much should that be?

Rob
 
well way back in the dark ages i was taught the rule of thirds with my tank

now after many years of diving, ive found the type of diving i like and have a fair bit of experience at my dive sites so i generaly like to come back with what is comfortabe for both me and my buddy (hubby)

i think your answer is going to depend on alot of factors as one size (answer) does not suit all

cheers and happpy diving
 
You'll quite often hear metric divers talk about "last 50 bar" or those using imperial about "last 500 psi". This works quite well as a general rule on most rec dives.

In reality, sometimes you'll use some of that air during your safety stops, but also you may finish the dive with half or even more than a half of your air supply left unused. It really depends on a dive.
 
So that you're still breathing when you reach the surface.

Actually, it's not so much about how much air with which you should end your dive, but more about how much air you need when you start and how much air is in your tank when you commence your ascent to the surface.

All of these are variables.

the K
 
A basic consideration is that if your buddy's regulator or tank has a major failure, that you need to have enough air available for the two of you to safely end the dive.

A search on "rock bottom" will reveal many threads about that topic.

While not perfect, a reasonable approximation of the needed reserve of air in an aluminum 80 tank is about 100psi for each 10' of depth, but never less that 700 or so for starting the ascent.

Some people will use a slightly higher number, such as 100psi/10' + another 300 or 400 psi padding. A new diver, with higher air consumption rate should add this much or more.

For example, if you are at 80' depth, you should start your ascent when you reach 1100psi or thereabouts. Assuming the normal case where you don't have to share air with your buddy, that should give you plenty of air to do a nice slow ascent, safety stop, and still have a reasonable reserve for doing an exit through surf or breathing on your reg while boarding a boat.

Again, it's not a case of how much air one should have left on the boat. It's a case of always having enough air for both you and your buddy to safely end the dive while both breathing the air from your tank. Your buddy is carrying your reserve air you will use if your tank or reg fails, so obviously it is in your interest for him to start the ascent with the proper reserve.

Charlie Allen
 
In a nutshell, "Rock Bottom" or what we refer to as "Bingo Air" (from a similar concept for aircraft fuel) is a calculation of when you should turn back (or begin to surface) on a dive. It is based on the concept that you (and for that matter your buddy) should always have enough air in your cylinder(s) to get you and your buddy back to surface without skipping required stops. The actual calculations are relatively simple.
 
robandliza:
As a basic rule of thumb, is there a certain amount of air I should always aim to have left in the tank at the end of a dive, and if so, how much should that be?
The question has several possible considerations, e.g. how to apply the rule of thirds, or at what pressure should you begin your final ascent, or how much air should you have after you are out of the water and on the boat or shore? I suspect you may be asking about the latter. Many dive boat operators tell people they want them to have a minimum of 500psi in their tank(s) when they get back aboard. If you have 450, they don't necessarily make an issue of it, although if you only have 100, they may view you as an unreliable customer, to the extent of not letting you do a second dive that you have paid for. Some boats do not care, so it is up to you. The 500 psi guide is a useful ROT. Whether I am diving an AL80, a steel 120, or doubles of these, I prefer to be on the ladder with 500, even though the cf of air remaining varies across these tanks and pressures.
 

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