Nitrox course. What's the point?

[tursiops]

Not yet, gotta add a long strap.

And paint it black.

 

[boulderjohn]

Most people do not use equations. They use the chart hanging on the wall of the shop that fills their tanks. Probably the majority do not even do that, simply remembering that 32% is good to 111 feet. When people dive with their nitrox-filled tanks, their computers measure the pressure and convert that to depth. They don't need to do any calculations there, either. That is why most people do not remember equations--they don't need to.

If, on the other hand, you are planning challenging dives at altitude, you need to do that calculating, because the charts are made for salt water at sea level. If you are, like me, making your own mixes in a motel parking lot, you need to do some calculating. If you are trying to make a mix that will take you safely to a certain depth and then when you measure the results you find you did not hit the mix you wanted, you have to plan a new dive, and you have to know the MOD options. If I am doing an ascent and want to switch to 50% nitrox, where I dive I can make that switch at 80 feet; at sea level it is 70 feet. But I don't feel like doing all that math all the time, so I made a MOD chart for the place I dive.

But that is advanced diving. For the purpose of the kind of diving being discussed in this thread, you don't need to know any of that. Even if you dive at altitude, for recreational dives you only need to know that the MODs for altitude are actually deeper than at sea level, so you can safely use the sea level MODs.

 

[rick00001967]

As an aside, nitrox use was also long-touted as being somehow "less fatiguing" than that of breathing conventional air; though, I have used it, off and on, since the early 1990s, when applicable, and have experienced no difference whatsoever -- that is, with the exception of a slightly lighter wallet . . .

ya i had always hoped this would be a big benefit as well. diving really seems to take a lot out of me. always has. but on the rare occasion i do use it i cannot say i have felt any real difference.
perhaps if i dived more it would be a bigger benefit ?
i def use it when it is f.r.e.e. or really cheap (like 5 bucks a tank) but i don't think i dive enough to make a real difference. on holiday my wife and i typically only do 10 or 12 dives over 2 weeks, and i have never done a liveabord for example.

 

[boulderjohn]

Actually, @Storker
Why DO dive computers let you adjust for salt water or fresh water? Yes, there is a difference in density, but all deco calculations are based on actual measured ambient pressure, right? If you were diving in mercury or using it in a hot air balloon, wouldn't you want the DC to know what the depth was in ATA, not in feet or meters? And this implies that adjusting your DC for salt or fresh water introduces an error rather than corrects for one.

I am afraid I don't understand this. I am evidently being unusually dense today.

The computer's depth sensor measures ATA, and the computer's software converts that to feet or meters for our benefit. If it is calculating NDLs, etc., it is doing that based on the pressure, not the numerical depth conversion. During my dive, my computer will give me a warning if I am too deep for the MOD of the gas I am breathing. If I am using 32% in fresh water at my altitude, my computer will be just fine with me breathing it at 115 feet, but it would be giving me a warning if I were in the ocean.

 

[boulderjohn]

perhaps if i dived more it would be a bigger benefit ?

In past threads, most people say a good way to see the difference is a week of diving on a liveaboard.

 

[doctormike]

if we are diving fresh water and the gauge reads 34 feet, our depth gauge (being calibrated for sea water) "thinks" we are in 33 feet of sea water and so will read 33 feet. (10meters)
so in reality, we can do all calculations "as if" we were diving sea water.

my only point was that the actual manual arithmetic that we teach on a white board in class is different for sea water than it is for fresh. this should be obvious.

Right, but maybe that's an error, maybe we shouldn't be teaching it that way. I guess the issue is that the depth gauge shouldn't read feet or meters, since those are dependent on what you are diving in. It should really read ATA, since that's the relevant variable that affects nitrogen loading and decompressions algorithms.

Now of course, I understand the educational difficulties of taking new divers and teaching that you are "1 ATA" under the surface - it just seems less intuitive than the idea of being "33 feet" under the surface. But I guess that distinction might be made when you are discussing the adjustments for fresh and salt water. Maybe that's the point to bring up the fact that you are actually measuring atmospheres, not feet.

Great discussion, as always! That's why I'm never that concerned about topic drift within reason - sometimes the side passages are the most interesting.

 

[BRT]

I hate when I see 33. Meters Vs Feet. Even though it is as simple as to divide or multiply by 3. I know that you guys are the kings of the world but why can’t you use metrics like the rest of the world ?

It's kind of a secret code. Like Pig Latin.

 

[Dody]

What does this mean?

It is partially a joke. I have never seen a dry suit just pictures, movies and people are like the Michelin bibemdum wearing it. Very different with the freedom of movement that one has with a wetsuit.

 

[doctormike]

I am afraid I don't understand this. I am evidently being unusually dense today.

The computer's depth sensor measures ATA, and the computer's software converts that to feet or meters for our benefit. If it is calculating NDLs, etc., it is doing that based on the pressure, not the numerical depth conversion. During my dive, my computer will give me a warning if I am too deep for the MOD of the gas I am breathing. If I am using 32% in fresh water at my altitude, my computer will be just fine with me breathing it at 115 feet, but it would be giving me a warning if I were in the ocean.

Right but the computer doesn't know that you are at 115 feet, it knows that you are at 4.5 ATA, and then it converts that to feet based on what you set it to (fresh or salt water). So you are determining whether or not you get a warning based on whether or not you set that toggle. It should give you the warning at the same ambient pressure, no matter what you are diving in, or no matter how many actual feet there are between you an the surface.

 

[doctormike]

It is partially a joke. I have never seen a dry suit just pictures, movies and people are like the Michelin bibemdum wearing it. Very different with the freedom of movement that one has with a wetsuit.

Well, if you have never seen a dry suit, maybe try one before you conclude that they restrict movement significantly. They certainly restrict movement a lot less than a heavy wetsuit, in my experience.