EAN versus "no-Fly" delay

[tbone1004]

@RyanT yes, but the problem is that with almost all computers on the market, you have no way of knowing "how much". You don't know if you can blow off a safety stop, you don't know if your no fly time has been reduced because they don't tell you your theoretical tissue loading *unless you have something like a Shearwater that spits that data out*. I was simply addressing the OP's question about EANx being safer than Air, and it is not. Adjusting your dive plans has nothing to do with EANx or not. @boulderjohn gave an example where the diver chose to end his dive before the NDL, that choice has nothing to do with diving nitrox or not. The perk of diving nitrox is his dive time was still longer than the NDL of air, but he chose to make his dive safer by cutting his dive time short of NDL's not by diving nitrox.

 

[Lorenzoid]

Yes, but nobody knows how much.

That's it in a nutshell.

DAN's current recommendation is not to fly for at least 18 hours after doing multiple dives or multiple days of diving (though 24 hours is a common recommendation for extra conservatism). As I understand it, due to the lack of data, etc., science cannot give us a more accurate number, so these numbers are conservative guesstimates. It's not like there is enough research out there on which DAN could base a recommendation such as "X hours if your dives were on air, but only Y hours if your dives were on Nitrox 28%, and only Z hours if your dives were on Nitrox 32%, etc. That would be slicing it more finely than science is currently capable of doing. So everyone just follows the conservative recommendations of 18 or 24 hours from DAN or other authorities no matter whether they were diving air or Nitrox.

 

[BoltSnap]

the original post in the thread....

That is not what he said and certainly it isn't "exactly"! You are over grossly thinking it.

 

[tbone1004]

there is actually a way to do it....
*disclaimer, this is not endorsed or recommended by anyone, including myself and any agencies that I am an instructor for, including DAN. Please do NOT try this*

Typical cabin pressure will max out at ~8000 ft. This is roughly 3/4 of an atmosphere. If you treat your last dive as an altitude dive at 8000ft, then you can basically fly immediately after the dive if you plan your decompression or NDL's appropriately. Why? you're basically saying that instead of surfacing at sea level, you are conducting the dive as if you were at the cabin pressure of the plane. Your NDL's will be short or your deco will be long, but it is possible to basically "trick" your body into decompressing to a point that it will not supersaturate at altitude. This is no different than the guys that live in the mountains and dive at sea level.

@BurhanMuntasser yes, that is actually what the OP said, it was a direct quote from the original post. He literally said reduces the risk of DCS, and asked if it could shorten or eliminate the FAD time. The answer to that is a resounding no. Nitrox does absolutely nothing for any of that. You can change your diving plans and nitrox will give you perks of lower N2 loading for equivalent depth and time vs. air, but changing your dive plans is what does what he is asking, not having a lower FN2 in the mix

 

[C P]

The perk of diving nitrox is his dive time was still longer than the NDL of air, but he chose to make his dive safer by cutting his dive time short of NDL's not by diving nitrox.

I agree with what your saying mostly, I don't agree that the only perk of nitrox is longer NDLs, but I'm not sure I read that as it was intended. Your bucket and my glass of tea examples say the same thing.
Another perk is using nitrox and planning the dive as if on air. The diver is obviously loading nitrogen slower and is at less risk of getting a hit. This is the whole premise of geezer gas .
Another perk is that if I want to one last dive before my trip ends, I just want a 30 minute goodbye dive, then I'm taking on less nitrogen if I dive nitrox than if I use air. The only way I could physically show someone this is to dive with two computers, one set to air and one set for nitrox. The computer set for nitrox will have a longer NDL during the dive, quicker return to depth for a repetitive dive, and a shorter wait to fly time than the computer set for air.

 

[Frontpointer1000]

All of my nitrox diving has been off a boat, diving with others, some of whom are on air. My son and I will dive together for instance. He's not nitrox certified. But dammit, kid, hurry up and get that cert...

What limits our diving (and that of the other boat divers) has almost always been the amount of air/gas, not the NDLs. Sometimes on deeper dives I approach an NDL, but I'm also approaching my comfortable limits of gas supply. I have certainly been diving with two computers, one set to air, one to the appropriate nitrox mix. It's great to see the NDLs separate over time. I like that SI, repetitive dives and potential dive times are all affected by nitrox diving. If I was a better breather, this would be more of an issue, but that comes with time and wrinkles. I'm patient.

In typical rec diving, unless you are down deep, it's hard to hit your NDL on nitrox before you run out of gas, especially on a typical rec dive off a boat with other divers. I'm sure I could play with the tables and find a scenario where this statement is false, that's the beauty of diving...It's not an exact science.

I assume tbone is likely diving twins with nitrox fills with other intentions than just diving for around an hour, certainly more than a typical rec diver does, and for that reason, it's difficult for him to see the reason or the benefit of nitrox except to increase the NDL time. I personally like to dive on nitrox because I like to pay more. It's a way of punishing myself for all the bad things I've done, and for those things not yet done, but that I will most certainly do.

 

[tbone1004]

for me I don't care about NDL's and haven't for a while because the number of dives where I don't go into deco are far fewer than the ones that I do. If you are gas limited vs time limited then yeah, Nitrox is a great tool to limit your tissue loading, but that is analogous to just diving a curtailed dive time. If you dove twinsets/doubles/sidemount whatever, then you could choose to stop the dive early, the nitrox doesn't magically extend your dive time.

I use nitrox to limit my decompression time which is basically the same as extending NDL's, but I also dive with very conservative profiles compared to most recreational divers and will be well into deco before most of them max their NDL's out. I do have a very good SAC rate and have no problem hitting NDL's with most tank sizes in a recreational environment

 

[Storker]

If you are gas limited vs time limited then yeah, Nitrox is a great tool to limit your tissue loading, but that is analogous to just diving a curtailed dive time.

Um, no. Going from being no-stop lmited on air to being gas limited on nitrox gives you both longer bottom time and lower saturation (alternatively, shorter SIs). Filling your single with nitrox is not analogous to "just diving a curtailed dive time". It's getting the most bang for the buck out of the gear you have invested in.

 

[Frontpointer1000]

for me I don't care about NDL's and haven't for a while because the number of dives where I don't go into deco are far fewer than the ones that I do. If you are gas limited vs time limited then yeah, Nitrox is a great tool to limit your tissue loading, but that is analogous to just diving a curtailed dive time. If you dove twinsets/doubles/sidemount whatever, then you could choose to stop the dive early, the nitrox doesn't magically extend your dive time.

I use nitrox to limit my decompression time which is basically the same as extending NDL's, but I also dive with very conservative profiles compared to most recreational divers and will be well into deco before most of them max their NDL's out. I do have a very good SAC rate and have no problem hitting NDL's with most tank sizes in a recreational environment

Always good information. I love SB because of the different (and sometimes differing) opinions and insights.

Tbone, as a new diver, I have no idea what a "good" SAC rate is. What is yours, out of curiosity?

I recalculate mine every few dives based on the various conditions, however, over time, may SAC rate is averaged at 20 ppm. Giving me a respiratory minute volume of .5 CF/min.

 

[tbone1004]

your SAC rate is your RMV.... same thing. though SAC is a more appropriate term than RMV if we want to be pedantic. SAC=surface air consumption, i.e. your consumption rate that has been normalized for the surface.

I assume 20ppm is psi/min?

In a recreational diving setting, mine is typically 0.4-0.5 depending on how fast I have to kick. 0.4 if I go my pace, 0.5 if I go most peoples pace. I kick slow... 0.5 is very good for any diver, especially a new one.