Diving Nitrox to increase safety AND bottom time!

[Zen Diving Inc.]

I have not yet dove Nitrox - the LDS course I took was a one-evening, two-hour session, all done in the local shop. I had picked up the SSI Nitrox booklet at Divetech a few weeks prior and was well prepped though. I'm the kind of guy who likes to know everything possible about what I'm learning and most certainly wouldn't have gotten that from the session alone (where the booklet wasn't offered).

I noted that the booklet made a reference along the lines of 'in your course you may dive Nitrox' but it didn't suggest that said dive was of particular importance. Not a sentiment I strongly disagree with since the differences between diving Nitrox and air come up in dive planning, not in the actual dive (MOD's notwithstanding).



m.

So my impression was correct, thanks for clarifying it. Aside from getting a dive out of your course i.e "bang for your buck" You also go thru the process of things like taking an O2 sample... Repetition is a good learning tool and practicing things like EAD while on the boat also quite beneficial between dives. You should always be able to fall back on something should your computer fail. Which does happen... Quite often within many brands, be it user error or just a crap computer lol. Know your tables, know how to calculate EAD, always wear a watch to back up your time and a depth gauge that records deepest depth that has to be manually reset and you will be a better diver for it.

 

[TheDeuce]

So my impression was correct, thanks for clarifying it. Aside from getting a dive out of your course i.e "bang for your buck" You also go thru the process of things like taking an O2 sample... Repetition is a good learning tool and practicing things like EAD while on the boat also quite beneficial between dives. You should always be able to fall back on something should your computer fail. Which does happen... Quite often within many brands, be it user error or just a crap computer lol. Know your tables, know how to calculate EAD, always wear a watch to back up your time and a depth gauge that records deepest depth that has to be manually reset and you will be a better diver for it.

Wise advice - I spin the bezel on my dive watch before I give the 'ok' post-giant-stride every time. For backup mainly but I've also gotten a kick out of table-tracking my nitrogen load to see how much more bottom time I'm getting from my trusty Veo 180 than I would have been getting 20 years ago.

I've learned to expect very little 'bang for my buck' from my LDS. Not getting a dive in on my nitrox course was no surprise....



m.

 

[lamont]

I think you're doing it wrong.

Assuming you're talking about this kind of SSI table (sorry, its in meters, but it should do):

http://2.bp.blogspot.com/_pMS8SLqYGrw/R7fO9zyNlXI/AAAAAAAADiM/NnMynFTPd4o/s1600/nitrox_table.gif

On a 30m/100ft dive on 21% you can go for 20 minutes and you wind up in group F
On a 30m/100ft dive on 32% you can go for 30 minutes and you wind up in group G

On a 24m/80ft dive on 21% you can go for 30 minutes and you also wind up in group G

What you are doing is essentially a 'shallower dive' as far as ppN2 is concerned so there's no accident that 30m/100ft on 32% is identical in NDL time and pressure group to 24m/80ft on 21%, that is what the entire "equivalent air depth" concept is about.

And if you do a shallower dive to the NDLs what you are doing is pushing your tissue compartment loading to slower compartments, that take more time to ongas and offgas so you wind up in higher, not lower, pressure groups.

To a certain extent you are a little safer by being shallower, though, by pushing the controlling tissue compartment to a slower compartment and reducing the loading in the fast compartments, which is going to help with bubble showers if you cork (assuming you don't have a PFO), but that is very 'meh' in terms of real numerical safety. I wouldn't bank on it at all.

The bigger 'safety' thing you can do is not cork. Learn to control your buoyancy, learn how to do stops in open water, make it so that you can hit a 3 minute safety stop, realiably, on every dive, even while task loaded. Imagine you are floating around at 15 feet some day and someone shows you a needle on a pressure gauge way into the red -- can you deliver a regulator to them without corking or dropping? What if they just throw an OOA signal at you? And say this is over an 80+ foot wreck dive with no hard bottom...

For bonus points... Add in being blown off the wreck... Can you get a bag up onto the surface for the boat to track and get yourself shallow, then handle your buddy sucking their tank dry while you're at your safety stop...

That is the kind of thing to focus on for safety... For nitrox, use it to extend bottom time. The bigger questions are if you've got the SAC rate to allow you to spend that much time at depth (i.e. how comfortable are you in the water), and if you've got skills to safely get back from depth?

 

[Moonglow]

I do NOT teach that nitrox is safer than air, it is used to extend bottom time only; all other reasons (for its use) are debatable.

 

[beaverdivers]

Nitrox has been so effective at reducing the risk of the bends that recompression chambers are going out of business.

 

[live_2_dive]

I do NOT teach that nitrox is safer than air, it is used to extend bottom time only; all other reasons (for its use) are debatable.

I respect your instructor omission that NITROX is safer than air (any instructor's choice to err on the side of being overly safe isnt bad IMO) but I would argue that it IS in fact safer at the same depth for the same time. That leads to the discussion of safer vs longer bottom time, but as for safety I would definitely argue it is.


-------------------------------------------
PADI Rescue/DM 09100Z7445
Dr Dive/Wet Dream/Sea Cobra/Y-Knot/H2OBelow

Diving is my passion...I live to dive!

 

[TheDeuce]

I do NOT teach that nitrox is safer than air, it is used to extend bottom time only; all other reasons (for its use) are debatable.

Do you mean you actively tell your students that nitrox is not safer than air? Or is it just that you're silent on the purported safety benefits, discussing only the extended bottom time?

If nitrox is only useful to extend bottom time then it would have no value to a diver with a higher SAC who's bottom time is dictated by their cylinder volume - would you tell such a student to avoid using nitrox since it would provide no benefit to them?



m.

 

[lamont]

Do you mean you actively tell your students that nitrox is not safer than air? Or is it just that you're silent on the purported safety benefits, discussing only the extended bottom time?

If nitrox is only useful to extend bottom time then it would have no value to a diver with a higher SAC who's bottom time is dictated by their cylinder volume - would you tell such a student to avoid using nitrox since it would provide no benefit to them?



m.

That student probably shouldn't be going that deep until they get more comfort in the water.

 

[AfterDark]

I respect your instructor omission that NITROX is safer than air (any instructor's choice to err on the side of being overly safe isnt bad IMO) but I would argue that it IS in fact safer at the same depth for the same time. That leads to the discussion of safer vs longer bottom time, but as for safety I would definitely argue it is.


-------------------------------------------
PADI Rescue/DM 09100Z7445
Dr Dive/Wet Dream/Sea Cobra/Y-Knot/H2OBelow

Diving is my passion...I live to dive!

Safer? Unless you exceed the mod or breath it too long. If its so safe why are there so many "safeguards" associated with its use? Training, stickers, analyers, log books. Air is safe to any sport diving depth for any length of time.

 

[TjRjn]

Taking a course with dives is absolutely crucial to getting value from it. It really isn't rocket science, and is something that could be easily self taught. If you have to pay $200 for the course, you might as well get a couple of free boat dives out of it.

Apparently it's not a PADI prerequisite to do a dive with the nitrox course anymore. It's now purely a classroom course.
I'm thinking of doing my nitrox for a variety of reasons and I've already told my centre that I want to do a couple of dives using nitrox. How can you possibly really know if you've not experienced?