Nitrox question

[junior diver]

thanks, i will take the courses, and for you people who have tried to put me off, you have not, i do not wish to do most of my dives in the area of which i have described, i shall carry on diving where i am now, around 50-60ft, i will be certified to go deeper, but that will only be for the odd dive what i think is worth all the extra work and planning, not jumping down to this depth every week, i know i will end up doing a 100% course, but as most of you have said on this matter, it will be for in water deco, probably at around 9ft, for all of you who have critisied me for wanting to do these courses, i can't stop you from critising, neither can you stop me doing the courses so i guess we've both got each other, i would really like to thank the people who gave me the calculations, they're great, im thinking of asking around at home for old nitrox tables so i can look up a bit more, and for Rick Murchison, do not wish to argue but i will never wish to be gods gift to diving, i dive purely for my own enjoyment and i hope you understand this, for Buccanneer, your philosophy of me being the typical 'deeper is cooler' diver, i am not, i dive deeper for the wrecks not the life down there, as i said, i am currently certified to 70ft but i do most of my dives at 50ft, please don't make this mistake about me, it even upsets me to be called this, Mikeferro , thanks alot, i don't know if you did this on purpose but it seemed to me that you sort of supported me, and dgallo, i did not mean it cool that they do 100% but that they did it for free for members, i thought that was unusual and cool in that way, i hope this post has made sense, really i do

 

[dgallo]

Ah, I totally misunderstood then. It is excellent that they do fills free for members.

Is membership expensive (relatively)? I pay about $35 (US) a year for my own dive club and I only get 10 free air fills. I also get other benefits, like a "club rate" on gear and boat charters. Just curious.

Good luck with your courses! I'm doing the Advanced class in July and from different discussions I've read about Nitrox it is definitely going to go on the list.

- David

 

[MikeFerrara]

thanks, i will take the courses, and for you people who have tried to put me off, you have not, i do not wish to do most of my dives in the area of which i have described, i shall carry on diving where i am now, around 50-60ft, i will be certified to go deeper, but that will only be for the odd dive what i think is worth all the extra work and planning, not jumping down to this depth every week, i know i will end up doing a 100% course, but as most of you have said on this matter, it will be for in water deco, probably at around 9ft, for all of you who have critisied me for wanting to do these courses, i can't stop you from critising, neither can you stop me doing the courses so i guess we've both got each other, i would really like to thank the people who gave me the calculations, they're great, im thinking of asking around at home for old nitrox tables so i can look up a bit more, and for Rick Murchison, do not wish to argue but i will never wish to be gods gift to diving, i dive purely for my own enjoyment and i hope you understand this, for Buccanneer, your philosophy of me being the typical 'deeper is cooler' diver, i am not, i dive deeper for the wrecks not the life down there, as i said, i am currently certified to 70ft but i do most of my dives at 50ft, please don't make this mistake about me, it even upsets me to be called this, Mikeferro , thanks alot, i don't know if you did this on purpose but it seemed to me that you sort of supported me, and dgallo, i did not mean it cool that they do 100% but that they did it for free for members, i thought that was unusual and cool in that way, i hope this post has made sense, really i do

When it comes to diving I don't try to encourage any one especially when it comes to deep or otherwise technical diving. However, I do know that if I had known earlier what was really available my dive career would have gone differently. I certainly could have saved a ton of cash and a lot of time.

You should get good training before doing it but I don't see the harm in talking about it or reading about it...knowledge is power and you'll be better able to plan your training and experience. You have plenty of time so just don't rush or forget to enjoy where you're at.

 

[GWP]

Just curious, how many of ya'll can come close to the bottom times you are talking about using single 80's? Somebody "sell" me on why nitrox is "better" when making relatively shallow dives < say, 70'. Assuming you are conservative anyway and not pushing the limits.

 

[fldivenut]

Somebody "sell" me on why nitrox is "better" when making relatively shallow dives < say, 70'. Assuming you are conservative anyway and not pushing the limits.

That's easy. At around 60-70 feet you can easy get into trouble on you second dive if you just "dive the tank empty", which seem to be quite common for people diving tables. I don't have any tables in front of me but 60-70ft gives you around 40-45 minutes, and then a second dive for as long as well. Even with a decent surface intervall (around 60 min) that is cutting it close. So with nitrox at that depth you are getting 60min+ for both dives. And another advantage is that you can cut your surface interval to what ever you need to change gear around and move the boat, usually much less than 60min.
Then there is the none proven things like that you feel better, less exhausted, less head aches, etc. when diving nitrox. You do, especially if you have to work a little underwater.
So the list is:
- Longer bottom times
- Shorter surface times
- Larger safety margin
- Less fatigue etc.
It's a no brainer really. I only do 30ft or less on air now days (or 180ft+).
--A

 

[Charlie99]

Just curious, how many of ya'll can come close to the bottom times you are talking about using single 80's? Somebody "sell" me on why nitrox is "better" when making relatively shallow dives < say, 70'. Assuming you are conservative anyway and not pushing the limits.

The depth at where nitrox becomes attractive is strongly influenced by whether the dive profile tends more toward a square profile or a multilevel dive.

FLdivenut gave a pretty good answer, but I suspect that his strong preference for nitrox is influenced a lot by his local dive sites. The 3rd reef in the Ft. Lauderdale-WPB area is a low profile reef that keeps you near your max depth for all of the dive until you start your ascent. For this sort of dive, nitrox is useful, even for dives in the 60-70' range and using single AL80. Almost all of the dives I've done in the Boynton Beach/Ft Lauderdale area have been on nitrox for this reason.

OTOH, if your dive site has lots of stuff of interest both at max depth and also up above 40', then it's easy to sequence your dive so that you go deep at the beginning and then gradually work your way shallower. With this sort of multilevel dive, I'm quite content to do 80' or 100' max depth dives on air.

Charlie


p.s. Here's the math that shows how quickly NDL can be the limiting factor even on a single dive at 66' (3atm absolute). Assume we will use 60 cu ft out of the AL80(about 700psi left). Air NDL at 66' is 40 minutes. You will hit the 40 minute limit before using 60cu ft if your at-depth air consumption is <1.5cfm. Adjusted to surface, this is 0.5cfm, which is not at all uncommon, and is well above my normal SAC of 0.4cfm.
As fldivenut pointed out, things get even worse if you then try to do a 2nd dive.

 

[DandyDon]

Just curious, how many of ya'll can come close to the bottom times you are talking about using single 80's? Somebody "sell" me on why nitrox is "better" when making relatively shallow dives < say, 70'. Assuming you are conservative anyway and not pushing the limits.

Using Padi Charts:

Here's one example: If I dive to 70 feet on air, I might get 40 minutes out of the 2,500# of pressure (3,000# full less 500# saved in reserved, unless I need it), and I'll be a T Diver.

If I take a 60 minute Surface Interval, I'll be a G, so if I want to return to 70 feet, I'll have only 22 minutes of Bottom Time left.

Instead, I'll plan on using 36% Nitrox on the second dive, so I'll have up to 49 minutes of Bottom Time.

Increased my Combined Bottom Time allowed on 2 dives from 62 to 89.

Here's another: For the S.Grove wreck, Duanne, Eagle, Thurnderbolt, A.Busch, i like to plan on 100 feet.

Air of 20 minutes, 60 min SI, do another 100 foot wreck dive for only 10 minutes.

Or, 32% Nitrox for 22 minutes, 60 min SI, and go back for 20 more.

For the Bibb, or most North Carolina Wrecks: I like 30% Nitrox.

Hope that helps...

 

[DA Aquamaster]

I tend to dive a lot on the weekend and 6 dives is pretty common over a two day weekend with another one thrown in on Friday evening if the weather is nice and I am in the mood for a night dive.

Before nitrox, even when staying within the NDl's, I tended to be a walking talking poster child for sub clinical DCS by Monday morning when I would crawl into the office looking and feeling like I had the flu. I feel better with nitrox and don't encounter the servere fatigue by Sunday night/Monday morning that I got after doing the whole weekend on air.

I also started using deep stops and accellerated deco for the deep diving which also gets me out of the water feeling much better. Accelerated deco gets you out of the water sooner (or alternatively lets you add a bit of a saftey margin to the stops without having to stay in the water longer) and is more reliable than doing the deco on air. I am not a big fan of 100% O2 as I normally only carry one deco gas. In that case I prefer 50% Nitrox as you can use it sooner and deeper (from 70' on up) and depending on the profile you can about the same time to only a few minutes later than if you were using 100% O2.

If you are planning on deep diving, an advanced nitrox course and a course covering staged deco procedures are a good idea after you complete a basic nitrox course and get comfortable with it.

I would agree with the caution to avoid diving too deep too soon. I did some really stupid things in my youth both diving and flying and I am lucky to still be here in more or less one piece. Deep diving is a whole lot safer once you overcome the youthful notion that you are invincible.

 

[narcT]

Tables can be good, but it your mix is 32.3 then:

1. 33 x 1.4 = 46.2

2. 46.2 / .323 = 143.03

3. 143.03 - 33 = 110.03

Your correct, but many people (like myself) were certified and dive PPO 1.6. So the person that said 132ft for EAN32 is correct...for me. I dive 130 on EAN32 for years. Again, this is a personal choice. Depending on how many dives I'm doing in a single day I might stay at 1.4 or even 1.2. But thats what the Nitrox class is for

33 * 1.6 = 52.8
52.8/.32 = 165
165-33 = 132

 

[miketsp]

Your correct, but many people (like myself) were certified and dive PPO 1.6. So the person that said 132ft for EAN32 is correct...for me.

I find that a strange statement. You were certified to dive PPO2 1.6!

I take it you mean that the current recommendation of your agency at the time you were certified was 1.6.

In the light of accident statistics, recommendations change.
There are military organisations that used 1.8 a few years ago and now use 1.4.