D Powell
Registered
Being very new to this and a bit wet behind the ears.
How long does a tank of air last
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gecko3s
Guest
most people will probably say an AL80 is about an hour.
But, it all depends on you breathing rate, the size of the tank, etc.. in short, it varies widely...
But, it all depends on you breathing rate, the size of the tank, etc.. in short, it varies widely...
If you are referring to the tank itself, ...years and years if you do some maintain it in good conditions.
If you are referring to the air in the cylinder, it depends on several factors.
Let's take a 15L cylinder with 200 Bars. That means 3000 L of air.
Now average breathing rate is 18-20L/minute (on the ground). taking 20L/min
that means 150minutes, that is 2 hours and a half. ON THE SURFACE
BUT going underwater you do not breathe air at 1 Bar.
Let's imagine you stay at 10 m depth. That means ambient pressure (pressure surrounding you) is 2 Bars.
That means that every breath you take consists of double the amount of air. If you consume 20L/min at sea level, you will consume 40L/min at 10 m. The air in the tank will last 75 minutes.
Summarising, you have to take into consideration your breathing rate and the depth you are diving.
Please note that breathing rate depends also on water temperature, water conditions, stress and so on. You will see that you will tend to consume less and less air along with your experience. This does not mean holding your breath, but breathing underwater exactly the same way you do when you are at home.
Please try to read again the laws of gases, like Boyle's low. That explains to you why you breathe different quantities of air at different depths.
ciao
If you are referring to the air in the cylinder, it depends on several factors.
Let's take a 15L cylinder with 200 Bars. That means 3000 L of air.
Now average breathing rate is 18-20L/minute (on the ground). taking 20L/min
that means 150minutes, that is 2 hours and a half. ON THE SURFACE
BUT going underwater you do not breathe air at 1 Bar.
Let's imagine you stay at 10 m depth. That means ambient pressure (pressure surrounding you) is 2 Bars.
That means that every breath you take consists of double the amount of air. If you consume 20L/min at sea level, you will consume 40L/min at 10 m. The air in the tank will last 75 minutes.
Summarising, you have to take into consideration your breathing rate and the depth you are diving.
Please note that breathing rate depends also on water temperature, water conditions, stress and so on. You will see that you will tend to consume less and less air along with your experience. This does not mean holding your breath, but breathing underwater exactly the same way you do when you are at home.
Please try to read again the laws of gases, like Boyle's low. That explains to you why you breathe different quantities of air at different depths.
ciao
How long is a piece of string? 
As you are posting in the new divers forum I don't know if you have done your Basic Open Water course yet? If you haven't then you will learn a lot then which will help you to understand this question a little more. There simply is no fixed answer BUT as you learn more and gain actual experience then it does become possible to make a reasonable estimate of how long a particular tank will last for you during any given dive when you know things like: your own air consumption at the surface/the depth of the dive you are doing/the size of the tank/the expected conditions during the dive etc.
It is also generally true to say that new divers use their tanks faster than the same diver with a bit more experience - i.e. you can make it last longer the more experience and practice you get.
p.s.Welcome to the board!! eyebrow
As you are posting in the new divers forum I don't know if you have done your Basic Open Water course yet? If you haven't then you will learn a lot then which will help you to understand this question a little more. There simply is no fixed answer BUT as you learn more and gain actual experience then it does become possible to make a reasonable estimate of how long a particular tank will last for you during any given dive when you know things like: your own air consumption at the surface/the depth of the dive you are doing/the size of the tank/the expected conditions during the dive etc.
It is also generally true to say that new divers use their tanks faster than the same diver with a bit more experience - i.e. you can make it last longer the more experience and practice you get.
p.s.Welcome to the board!! eyebrow
Marek K
Contributor
...and depth!!gecko3s:
I assume you're very, very new at this
... if you're just trying to get a ball-park idea (do Brits use that expression?) of how long you'll be able to stay underwater at a time, then Gecko has it right... about an hour, at a depth of about 30-40 feet (10-12 meters).--Marek
BMETdiver
Registered
The other thing you will have to consider is how good of shape you are in, I am a larger build but in relatively good shape and suck up air pretty quickly but have had dive partners who are out of shape and I still have 1000PSI when they are at 500.
Marek K:
Actually I've seen a diver who can suck a 12 liter tank (about 85 cu/ft) down in around 20 minutes at those depths, in good tropical conditions (Tioman, Malasia), with no current. Suffice to say he wasn't very popular on the boat as he'd told everyone he had around 80 dives.
There were several other things about him that made you want to be somewhere else as well.
D Powell:
Kim, I have found that with warm water, a 30-40 ft. depth, and a relaxed streamlined profile I have improved from about 35 min for an 80 cu ft tank to more than an hour and 20 to an hour and 30 minutes. Obviously, I have been doing this a while but once you begin to get comfortable and learn how to control yourself and your breathing your time underwater will increase substantially. Just pay very close attention to the number of "things" you have hanging off your BC as they all create drag in the water and that equates to more effort and less bottom time. Enjoy and read and learn all you can.....it makes you more comfortable in the water! http://www.scubaboard.com/newreply.php?do=newreply&p=1285996#
Wink
Also, the change may not be sudden, but cumulative over time.
You notice it when you dive the same site frequently, realize that you're running 25% more time than you were a bit earlier.
You notice it when you dive the same site frequently, realize that you're running 25% more time than you were a bit earlier.
m3830431
Contributor
My first dive to 80 feet lasted 18 minutes with a Al 80 cu.ft at 2900 psi and that was with a 3 minute safety stop. I gets allot better with time.
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