Multiple dives, multiple days..Nitrox

[jepuskar]

Hi,

My buddy and I are thinking of using Nitrox for 7 straight days of atleast 4 dives a day. We both have Nitrox compatible computers, but have never dove over multiple days with Nitrox.

We are going to Bonaire, so we probably could get away with using 36% the whole trip, but would be pushing the 24 hour exposure limits..according to the tables anyway.

Any deep dives like the Hooker would probably be done on air or 32%.

Has anyone dove this much exclusively on Nitrox for multiple days and used a computer? If so, what % did you use and were you even close to reaching your exposure limits?

We have multiple options on how to use Nitrox, like using 36% for our last few shallower dives of the day..etc.

Any insight would be appreciated.

Thanks,

Jason

 

[MikeFerrara]

It's hard to say without looking at a specific series of profiles. Depending on the dives I might be inclined to throw a lighter day or so in there someplace. That really doesn't have anything to do with O2 exposure though.

What they usually don't teach in a basic notrox class is that the rest of us take SI credit for CNS exposure.

Chances are your computer will give you SI credit also. Check the book for the computer. A half time of 90 minutes is common

 

[Scubamedicjoe]

personally i would limit it to three dives a day and what your total time rea; close also watch depth , time and amount of surface time also affect it.

 

[jepuskar]

Mike,

Yes, the computers do give credit for SI and obviously your actual depth throughout the dive..unlike the tables I am looking at....just haven't used nitrox over multiple days like we are planning.

Medic,

We are planning to do 4-5 dives a day and the option is there for us to just use Nitrox on the last 2-3 dives as these will be less than 60 feet more than likely....

We have looked at our dive profiles from our last trip to Bonaire..deepest was 99ft, average I would say is in the area of 50-60 feet....surfaced with about 1000psi, 4 dives a day...... could we get away with using air the whole time....sure we could.

The one thing I don't understand about Nitrox is that it significantly lengthens your no deco stop time, however, it doesn't reduce your chances of DCS by that much, using even an air profile...this confuses me.

How can they say its ok to dive x amount of minutes more, which in some cases is quite alot, and then say, ohh yeah, you pretty much still have the same chance of DCS even if you do dive an air profile......can someone explain that to me?

Jason

 

[mempilot]

My LDS owner and his wife went on a liveaboard last fall. They dove 4-5 tanks of nitrox a day for a week. Her computer maxed out the O2 exposure the morning of the last day. Rather than trick the computer by programming a different mix, she just dove the last couple of dives on air.

 

[ninjamuzo]

Remember that besides the 24 hour limit you have to keep track of your cumulative OTU count this is normally not an issue (depending on your dives) for a day or two but it will become a factor on high O2% dives over time.

Most technical diving books have these tables in them.

 

[rjchandler]

Mike,
SNIP
The one thing I don't understand about Nitrox is that it significantly lengthens your no deco stop time, however, it doesn't reduce your chances of DCS by that much, using even an air profile...this confuses me.

How can they say its ok to dive x amount of minutes more, which in some cases is quite alot, and then say, ohh yeah, you pretty much still have the same chance of DCS even if you do dive an air profile......can someone explain that to me?

Jason

The argument is that your chance of DCS is so low to begin with that you can't really reduce it mich farther. It gets argued about a lot.

I usually do Bonaire on the type of schedule your describing and the CNS buildup does not become a problem. This is even with an Oceanic computer which requires 24 hr to clear the cns clock.

 

[jepuskar]

Joe,

Do you use 32% or 36%?

thanks,

 

[rjchandler]

jepuskar - i use 32 (or 31 or 33 or 29 - depends on what the outfit i use has available ). You may find that 32 is all that is available - depends on where you get your tanks.

 

[jepuskar]

Ok, thats cool.....I will be staying at Captain Don's....since they have rebreather training there...I will assume they have 36%, but I'll settle for 32%.

thanks again