Nitrox resources

[Soggy]

At 40M, you'd have to to be breathing something like nitrox 28 and you'd get 10-15 minutes.

I would be happy with 25 min at 40m, compared with 5 or 10 min on air. For trimix I'd probably need another certificate, so it's not doable right now for me. Thanks for the info.

 

[*Floater*]

Floater,
Soggy was being very nice to you - it's not a certificate you need - it's dive time, experience, knowledge and patience. Your goal right now should be consolidation of your OW/AOW skills and Rescue skills. Nitrox is a good course but your lack of diving knowledge is very apparent in the questions you ask and while I might be coming across as an *********** I really do hope you appreciate that it's because I sincerely believe that you may be a candidate for an incident.
I apologize to anyone who thinks I might be out of line here but it's out of concern for the poster and is not borne of malice.

How much consolidation do you think I should do before I get Nitrox certified? Most of my dives have been fun dives (about 70% of them), so I'm not just about piling up certs, and while I realize I'm still a newbie I have heard of people taking Nitrox in conjunction with their OW cert.

As for deep diving, I'd like the certification so I can learn how to do it safely and then visit a number of great dive sites that are currently not available to me.

The nitrox workbook I posted a link to lists 132 ft (or about 40m) as the NOAA's MOD for EANx32 (warm water, <45 min dive), so doing a 40m dive on nitrox seemed like a possibility to me, which is why I asked. Also, some centers/agencies recommend combining the two. For example, this is from IANTD's website: http://www.iantd.com/iantd3.html

Nitrox Diver

This program provides recreational divers a safer breathing medium for enjoying dives in 40 fsw (12 msw) to 130 fsw (39 msw) depth range. The diver may elect to dive the mix on EANx tables or conservatively using their dive computers or air tables with an added diver safety margin. The IANTD Nitrox Diver certification is adaptable to being taught as a single program or by combining it with a variety of advanced or specialty diver courses.

Deep Diver

This program has been developed to provide responsible training to divers who plan to dive to 130 fsw (39 msw) on air. The IANTD Deep Air Diver program trains divers in skills, performance, theory and planning of deep dives. This program remains within the commonly practiced depth of 130 fsw (39 msw). It is the first sanctioned program to provide proper international training in safe deep diving skills and performance. It is recommended that this program be taught in conjunction with the IANTD EANx Diver program.

But I have heard people say that one should not use Nitrox for deep diving as well, which is why I'm here asking about it to get the facts straight.

 

[dbulmer]

Floater,
Don't ask me a person with only a few more dives than you have. Speak to a qualified instructor or perhaps PM an instructor on the board.
What I think they might ask you to consider is your buoyancy control, your ability to plan a dive (ie gas planning, deco schedule), your ability to choose appropriate equipment, your situational awareness and underwater problem solving ability, how you manage stress in yourself and your buddy. You can pick up some information on this from courses and from talking to qualified people but you also have to be able to put the theory into practice in the water where it counts. A simplistic example, for Nitrox you have a Maximum Operating Depth ie you need to have the mental discipline to keep above this depth and have the buoyancy control to ensure it.

For stops have you considered doing shallow dives less than 6 metres to hone your skills in that area?

 

[Azza]

The nitrox workbook I posted a link to lists 132 ft (or about 40m) as the NOAA's MOD for EANx32 (warm water, <45 min dive), so doing a 40m dive on nitrox seemed like a possibility to me, which is why I asked

Yes it's the MOD alright, but not the Maximum Working Depth. The Maximum Working Depth for ean32 is 33.7 metres which gives a PPo2 of 1.4 ata.
At 40 metres you will have a PPo2 of 1.6 ata, which is ok for decompressing on but not for bottom time.
Please dont dive ean32 at 40 metres, I dont want to be reading about another dead diver...

 

[Atticus]

Hi Folks, perhaps I can help a little with this question. I teach recreational deep and nitrox, and am a certified trimix diver.

The "nitrox is not for deep diving" issue is based on the maximum safe depth of a gas. A reasonable working partial pressure of oxygen (ppO2) is 1.4.

At 40m you're at 5 ata. 1.4 ppO2 / 5 ata = 0.28 fO2. This is the fraction of oxygen which is reasonably safe to breath at this depth (28%). The no decompression limit at sea level with 28% at 40m is going to be in the ballpark of 15 minutes as opposed to 10 minutes on air (NOAA tables - please don't take this as a dive plan - do your own research with the assistance of an in person instructor!).

Some programs instruct their students to mark their tanks with an MOD (Maximum Operating Depth) based on a 1.6 ppO2. This is the deepest depth the gas should be breathed at and is not for the working portion of the dive (ie: swimming around). The 1.6 ppO2 at 40m is 32%. The NDL on 32% at 40m is 20 minutes. I would urge you not to consider this a reasonable dive profile - 1.6 should the planned ppO2 of a recreational dive.

So - as you go deeper the fraction of oxygen you can breath decreases. This is why people say nitrox is not for deep diving. For dives in the 80' - 130' range it can be quite useful for extending you NDL's.

One thing to keep in mind is that divers frequently run low on gas prior to hitting their NDL's. If a normal person breathes 1 cubic foot per minute on the surface, then at 40m they will consume 5cf/m. This means that an alu80 is empty after 16 minutes.

At that depth you need to spend about 7 minutes ascending (at 30'/minute - NAUI's rule, plus a 3 minute safety stop). That's about 15 cf. You'd like to be able to bring your buddy up if he has an emergency / runs out of gas (another 15 cf), and you'd like to have a 500 psi reserve (another 13 cf). That's 43cf, or about 1600 psi that you need to have when you begin your ascent. That gives you 37cf (assuming an alu80 is actualy 80 cf which its not quite), or about 7.4 minutes.

If you want to enjoy the increased NDL time from nitrox at this depth then you need to get a larger tank (doubles are nice), or reduce your breathing rate.

Something else to keep in mind is that an ascent from 40m should probably not be just a straight 30'/min with a safety stop. Some intermediate deep stops will help your body out quite a bit. Take a look at NAUI's new ascent rules (search for NAUI Rule of Halves).

Please feel free to comment / PM me / etc. If you see any mistakes in the above or would like an additional explanation I'm happy to hear that too.

Best Regard,
Merlin

 

[captnkurt]

I think dbulmer is right with the patience thing. I have 38 dives since april and a huge desire to progress rapidly, but not to fast. Take it easy and very safe, I live in puerto vallarta and know that all dive operations are different in what they offer, so be careful of the ones that offer anything you want!!

 

[Soggy]

I'm one of those guys that believes that nitrox should be taught as part of OW. It's not rocket science and *can* increase your safety margin dramatically if you don't violate your MOD. Personally, I don't dive below 40-50 ft or so without EAN32....air is pretty much relegated to shallow shore dives for me.

 

[dbulmer]

Soggy,
I think that Nitrox as part of AOW with a formal re-evaluation of OW skills by an instructor at AOW level would be better. I'd worry that the safety aspects of Nitrox would be negated by (serious) violations of MOD caused by poor buoyancy control. (GUE excepted of course ). I also think that at AOW level it should be mandatory for Gas laws to be covered - I know some instructors teach this at earlier levels but from from what I have seen on Scubaboard and other forums such instructors are in the minority.

Merlin,
On the basis of your experience what would you be suggesting to *Floater*? ie what would be your road map for someone wishing to do a 40metre dive for 40 minutes?

 

[*Floater*]

Thanks to the people who cleared up the nitrox/deep thing. Now that I have a better understanding of it, I'll just probably just take nitrox to begin with, and if I do the deep diver specialty, then I'll do the 40m dives on air for 5-10 min, or whatever they teach me during the course.

Of course, the deep diver cert seems a lot less desirable right now since 5-10 min dives aren't that appealing to me and to extend my bottom time I should probably learn a lot more about other gases and techniques, which is not in my planned budget for the next dive trip.

 

[Atticus]

...Merlin,
On the basis of your experience what would you be suggesting to *Floater*? ie what would be your road map for someone wishing to do a 40metre dive for 40 minutes?

This happens to be my favorite kind of dive -- lots of time to enjoy things that many consider too deep to visit.

The classes needed for this type of dive are:

a. Nitrox
b. Rescue (may not be required but probably should be)
c. Deep (because many agencies require it before going into tech)
d. Technical Nitrox / Technical diving fundamentals
e. Deco Procedures
f. Helitrox (real deco, light helium)
g. Normoxic Trimix (not required for the depth we're talking about, but gives you more knowledge & confidence for these types of dives).

Along the way you want to get 100-200 dives to build your experience. This should take 1-3 years of fairly serious training. If it looks like there's a faster way then ask a LOT of questions. It's not about the card, it's about the about the training. You really don't want to go from zero to hero.

The following is from VPlanner www.v-planner.com. You could shorten this profile up a little by running 28% instead of Tx21/35, but then you are at your MOD so you can't explore vertically.

40 minutes, Trimix 21/35
13 minutes, EANx50
20 minutes, Oxygen

Total time: 75 minutes
Total Tx21/35: 160 cf (240 cf required for thirds)
EANx50: 25cf
Oxygen: 23cf
RMV of 0.8 cfm

To do this dive I would use a set of LP104 doubles with a slight overfill and two alu40's for deco gas.

If you chose to do this dive on EANx28 only (no EANx50, no oxygen) then your total runtime would be 109 minutes.

*** Please do not try to do this type of diving without the proper training. ***

EDIT: Removed exact profile to keep my conscience clean.