Take 4 oz of water in a glass, and 4 oz of kool aid in another. The sweet kool aid tastes better. Drink both down. The glasses empty just as quickly.
Nitrox question
- Thread starter naplestreasures
- Start date
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Next time you're at the dive shop, show her a 6 (or 13) cu ft tank, then show her a 120 cu ft tank.
Ask her if she thinks that if she fills the tiny tank with nitrox and the big tank with air, does she still think that the little tank will still give her more bottom time than the big one.
Watch her eyes for the epiphany.
Ask her if she thinks that if she fills the tiny tank with nitrox and the big tank with air, does she still think that the little tank will still give her more bottom time than the big one.
Watch her eyes for the epiphany.
Actually, even if I have the same bottom time, my goal is to always leave the water with as few balls in my bucket as possible.
mksmith713
Contributor
Excellent but....... How about I add this.[/COLOR]
The 4 oz glass of water is better for you so you can drink more without getting rotten teeth and fat?
mksmith713
Contributor
I don't suppose she's contemplating diving double?....... 
Then it might be advantageous to use EANx......
Then it might be advantageous to use EANx......
Hmmm...we have analogies up the wazoo here.
Fact is, if she needs an analogy and cannot understand the gas and deco planning involved, she needs to stick with air until she can articulate the advantages and disadvantages of Nitrox to you.
I had a boss once whose sum total of mechanical knowledge is that when the car quits you pull the long thingy out of the engine and look at it. To him this form of immediate action was readily apparent since he had always seen mechanics and service station people do that (check the oil level) all the time. The moral of the story is that if dip sticks were nitrox you would not want that "dipstick" diving nitrox.
Make it homework assignment where she researches the issue and reports back to you. Keep her at it until she gets it right. It will stick a lot better if she goes to the effort of learning it herself.
Fact is, if she needs an analogy and cannot understand the gas and deco planning involved, she needs to stick with air until she can articulate the advantages and disadvantages of Nitrox to you.
I had a boss once whose sum total of mechanical knowledge is that when the car quits you pull the long thingy out of the engine and look at it. To him this form of immediate action was readily apparent since he had always seen mechanics and service station people do that (check the oil level) all the time. The moral of the story is that if dip sticks were nitrox you would not want that "dipstick" diving nitrox.
Make it homework assignment where she researches the issue and reports back to you. Keep her at it until she gets it right. It will stick a lot better if she goes to the effort of learning it herself.
Well along with everything else here....here is some math that might help.
Using the good old Aluminum 80 as an example, 80(rated volume of tank)/3000 (tank's rated pressure) = 0.026
If the tank is filled to let's say 3300 psi then
3300 x 0.026 = 85.8 cuft of gas...doesn't matter what kind of gas...it is the same volume of gas irregardless.
So...we dive to 65 feet (saltwater) for total of 40 minutes. (Freshwater use 34 as the divider instead of 33)
(65/33) + 1 = 2.96 atmospheres pressure.
assuming a surface consumption rate (whatever yours/hers might be) of 0.6 cuft/min with 40 TOTAL minutes of time (excluding a 3 minute stop @ 15').
(2.96 x 0.6) x 40 = 71.04 cuft of gas required for the dive. It doesn't matter what kind of gas...you will still need 71.04 cuft of gas...plus let's throw in the 3 minute stop at 15'.
(15/33) + 1 = 1.45 ATA
(1.45 x 0.6) x 3 = 2.61 cuft.
So in total 73.65 cuft required for a total...including your descent, ascent, and stop times, of 43 minutes total submerged time (you will hear this referred to by tech divers as "runtime"). It doesn't matter if you are using air, EAN 32, or Tx 19/40....you have to have 73.65 cuft of whatever you are using to do the dive.
How much left over? 85.8 - 73.65 = 12.15 cuft left.
Convert volume to psi 12.15/0.026 = 467 psi left in tank.
In reality all things equal, it would probably be a bit more because descent and ascent were calculated at the pressure of 65 fsw, plus most recreational dives depth is not a constant...thus the advantage of a computer, but we are calculating...for the most part on the conservative side.
So of all those numbers up there...what can we control? Well tank size and fill pressure to some extent, but the one that you can improve (as you pointed out in your post) is consumption rate. You can run those problems with different consumption rates and see the effect of breathing on the volume of gas used. It can play a fairly large role. As an illustrative example...a consumption rate of 0.7 would not be able to do the above dive...they would run out of gas.
This is a very simplistic example of gas planning, (we aren't going into rule of thirds or half + 200 depending on dive conditions, or calculating for different members consumption rates and if divers have different cylinder sizes, turn pressures, etc etc).
The advantage EAN gives is (I am speaking to recreational diving situations) in terms of bottom time in relation to no decompression limits as EAN gives you a lower value in terms of nitrogen exposure than conventional air...which allows you to have a longer bottom time relative to no decompression limits on your first and subsequent repetitive dives but in terms of physically changing the amount of time I can get from a cylinder of gas...it does nothing. It does not allow you to stay longer than the physical limits of tank volume/pressure versus depth versus consumption rates are concerned. Those are physical laws.
We also aren't talking about CNS and OTU calculations...which if you are diving EAN, need to be tracked, especially if you are doing repetitive dives over the course of several days. Generally OTU isn't much of a concern for recreational EAN...but does come into play when using high O2 content gas for deco on deep dives with long run times. CNS does need to be watched in diving situations like liveaboards where you could be knocking down 4-5 dives a day over the course of a week, but should be tracked on all dives so the diver is put into the habit of habitually monitoring it.
Using the good old Aluminum 80 as an example, 80(rated volume of tank)/3000 (tank's rated pressure) = 0.026
If the tank is filled to let's say 3300 psi then
3300 x 0.026 = 85.8 cuft of gas...doesn't matter what kind of gas...it is the same volume of gas irregardless.
So...we dive to 65 feet (saltwater) for total of 40 minutes. (Freshwater use 34 as the divider instead of 33)
(65/33) + 1 = 2.96 atmospheres pressure.
assuming a surface consumption rate (whatever yours/hers might be) of 0.6 cuft/min with 40 TOTAL minutes of time (excluding a 3 minute stop @ 15').
(2.96 x 0.6) x 40 = 71.04 cuft of gas required for the dive. It doesn't matter what kind of gas...you will still need 71.04 cuft of gas...plus let's throw in the 3 minute stop at 15'.
(15/33) + 1 = 1.45 ATA
(1.45 x 0.6) x 3 = 2.61 cuft.
So in total 73.65 cuft required for a total...including your descent, ascent, and stop times, of 43 minutes total submerged time (you will hear this referred to by tech divers as "runtime"). It doesn't matter if you are using air, EAN 32, or Tx 19/40....you have to have 73.65 cuft of whatever you are using to do the dive.
How much left over? 85.8 - 73.65 = 12.15 cuft left.
Convert volume to psi 12.15/0.026 = 467 psi left in tank.
In reality all things equal, it would probably be a bit more because descent and ascent were calculated at the pressure of 65 fsw, plus most recreational dives depth is not a constant...thus the advantage of a computer, but we are calculating...for the most part on the conservative side.
So of all those numbers up there...what can we control? Well tank size and fill pressure to some extent, but the one that you can improve (as you pointed out in your post) is consumption rate. You can run those problems with different consumption rates and see the effect of breathing on the volume of gas used. It can play a fairly large role. As an illustrative example...a consumption rate of 0.7 would not be able to do the above dive...they would run out of gas.
This is a very simplistic example of gas planning, (we aren't going into rule of thirds or half + 200 depending on dive conditions, or calculating for different members consumption rates and if divers have different cylinder sizes, turn pressures, etc etc).
The advantage EAN gives is (I am speaking to recreational diving situations) in terms of bottom time in relation to no decompression limits as EAN gives you a lower value in terms of nitrogen exposure than conventional air...which allows you to have a longer bottom time relative to no decompression limits on your first and subsequent repetitive dives but in terms of physically changing the amount of time I can get from a cylinder of gas...it does nothing. It does not allow you to stay longer than the physical limits of tank volume/pressure versus depth versus consumption rates are concerned. Those are physical laws.
We also aren't talking about CNS and OTU calculations...which if you are diving EAN, need to be tracked, especially if you are doing repetitive dives over the course of several days. Generally OTU isn't much of a concern for recreational EAN...but does come into play when using high O2 content gas for deco on deep dives with long run times. CNS does need to be watched in diving situations like liveaboards where you could be knocking down 4-5 dives a day over the course of a week, but should be tracked on all dives so the diver is put into the habit of habitually monitoring it.
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That's funny, since you then went on to prove your point using the mechanics analogy.
Hook a reg up to an unmarked tank, then have her breathe on it at the surface. Now ask her if she was breathing nitrox or air. She will say either I don't know or guess one or the other. So now you submit to her that without analysis there is no way to tell by just breathing. So air and nitrox are the same from the breathing perspective, therefore you will breathe them at the same rate, right? Now show her that if she had unlimited nitrox to breathe, she could extend her bottom time. Use air tables next to nitrox tables to demonstrate the difference.
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