High END

Hi guys,

Sorry if this is in the wrong Forum.

I'm fairly new to diving (30-40 dives) and have just bought my first dive computer (D4i).

I've been messing around with the dive plan software and on one of the plans I made up theres a point where it says 'High END'.
I understand this to be the 'Equivalent Nitrogen/Narcosis Depth'... now then, the issue I have... I don't fully understand what it is!
I've been doing some searching on forums and Google to try and find out the answer but the descriptions are a little too technical for me! Could someone 'dumb it down' enough for me to understand?!

Cheers,
Chris

How deep was the plan?

35m, 'High END' was at 26m

END is an attempt to measure the narcotic effect of a gas/depth combo relative to air.

So the END of a 100' (30m) dive on air is 100'.

But what happens if we add some helium to the mix? Lets say we dive a gas with 30% helium to 30m. Since there is LESS narcotic gas (o2 nad n2) in the mix, the new END is 18m.

Lets go deeper. 50m now, with the same 30% helium mix (o2% is for a different discussion), the END at 50m is equivalent to air at 32m. Upping the helium content to 45% drives the END down to 23m.

Helium is good, narcosis is bad. Helium makes narcosis go away.

If I had to make a guess, I'd say that whatever dive plan you're playing with has an END past about 30m or so, hence triggering the warning. Generally, ENDs greater than about 30m are suggested against.

When you dive and go to depth, the effect of the gases you breathe increases with depth because of the fact that it takes more molecules of each gas to fill your lungs as you get deeper. At 4 atmospheres of depth (30 meters), you are breathing in 4 times as many molecules of oxygen and nitrogen as you were at the surface, and this has an impact on you in several ways.

When you breathe something other than air, that impact is different. Nitrox has more oxygen in it, and therefore less nitrogen. So the effect of nitrogen at the depth you are diving is equivalent to the level of nitrogen at a different depth when diving air. This has an impact on the amount of time you can stay at that depth, because the amount of nitrogen being absorbed into your system determines when you need to begin your ascent.

Nitrogen (and oxygen as well) also impacts narcosis. In part because of that, technical divers add helium to their breathing gas, which cuts down on both the amount of nitrogen and the amount of oxygen. Once again, the amount of narcosis-inducing nitrogen in the system at their diving depth will be equivalent to the amount of nitrogen in air at a much shallower depth.

In non-technical diving(i.e., no helium in the mix) END only makes sense if you consider nitrogen to be narcotic, but not oxygen. There is still some disagreement, but they are often considered to be equally narcotic these days. If you're going to use the concept for nitrox mixes, you compare the amount of N2 you're breathing at a certain depth on nitrox to the depth in air that would give the same amount of N2. e.g., at 132'(5 ATA) on 28%, your ppN2 is 5*.72, or 3.6 ATA. To get 3.6 ATA of N2 on air, you'd be at 117'. There are formulas and tables to speed things along, but unless I'm diving trimix, I don't consider the difference.

(If I was breathing 21/35 on that 132' dive, I would consider the END to be (1-.35)*5 ATA, or 75'.)

Oh ok, think I have it.

So... with the example above,
"Lets go deeper. 50m now, with the same 30% helium mix (o2% is for a different discussion), the END at 50m is equivalent to air at 32m. Upping the helium content to 45% drives the END down to 23m."

With the END at 50m (with the above gas mix) you're effectively going to have the same effect (narcosis effect) as you would if you were diving with air at a depth of 32m?

If this is correct, I take it it would be good to note down the range you start to feel affected by narcosis (on air) and when tec diving adapt your mix to create a END lower than that range?

I think you've got the gist of it.

The issue with your idea though is that you're impaired while making an evaluation of your impairment level. Its like when drunk folks say "I'm fine to drive!" and we all know better.

Some/many/most people use 100 fsw as the max END. Judging when you "feel" narced is a slippery slope. You are already impaired by the time you feel it and it is situation dependent and can change from dive to dive.

Sent from my SM-N900V using Tapatalk 2

PfcAJ,

Yea I understand what you mean, I just thought that was the best way to explain what I was thinking.

Effectively you want it as low as possible is what I should have wrote perhaps.

Cheers for the replies, much appreciated!

Chris