Liveaboard Nitrox surcharges - Time for this to go...

[kaerius]

Hard to get even close to 02 limits unless you're doing five long DECO dives a day. I do five dives a day for a week or two at time when traveling on dive trips and never even came close. Even in Truk where I did 4-5 deep dives on 28-24% with varying degrees of deco for 17 days straight I didn't come anywhere close to 02 limits.

Depends on the mix I guess, but I've been up to 50% on two dives(32% and 36%). No deco. These are the two most popular and common mixes, or so I keep being told. This with 30m and 26m maxdepths, on multilevel dives. You basically need to do 4-5 dives to hit the limit... but I wouldn't want to get that close(say 80%+) several days in a row.

 

[RJP]

Depends on the mix I guess, but I've been up to 50% on two dives(32% and 36%). No deco. These are the two most popular and common mixes, or so I keep being told. This with 30m and 26m maxdepths, on multilevel dives. You basically need to do 4-5 dives to hit the limit... but I wouldn't want to get that close(say 80%+) several days in a row.

Unless I'm missing something, that's just not possible.

I just ran recreational dive profiles in V-Planner for 36% at max depth for max NDL and even if you did EIGHT dives a day for SIX days straight you'd not hit the OTU limit. (OTU being the important unit for pulmonary tox)

Two dives at max exposure to 36% gives you 104 OTU's which is only 12% of the 850 OTU/Day max for single day exposure. If you did EIGHT recreational dives on 36% to 100' for full NDL you'd STILL be under 50% of daily OTU (48.9%)

If on the other hand you're talking about CNS O2 exposure, you'd be hard pressed to hit 50% CNS exposure on recreation profiles unless you were doing ultra-short surface intervals. The aforementioned EIGHT dives to 100' for max NDL hits 42% of the CNS exposure if you do 1.5hr surface intervals. If you did 1hr SI's it would still take you 5 dives to 100ft for full NDL to hit 50% of CNS clock, and you'd run out of day long before you'd run out of CNS clock. (Ten dives only gives you 52.6% CNS exposure - V-Planner won't plan more than 10 dives in a 24hr period)

In fact I cannot calculate a two-dive recreational series that gives you 50% CNS exposure with 36% EANx. A ONE MINUTE surface interval between two full NDL dives to 100ft on 36% only gives you 44% CNS total (and also causes you to have 24min of mandatory deco.)

 

[kaerius]

Maybe we're using different tables(or you're using formulas). I use the PADI/DSAT O2 exposure table.

Let's see, dug up my profiles:
Dive 1:
EAN32
27 meters, EAD 24.4, 21 minutes, PPO2 1.28, PG M, NDL 27
20 meters, EAD 15.8, 15 minutes, PPO2 0.96, PG S, NDL 24
12 meters, EAD 8.9, 13 minutes, PPO2 0.7, PG U, NDL 88
O2 exposure 25%(15+5+5)

Dive 2:
EAN36
22 meters, EAD 15.9, 26 minutes, PPO2 1.15, PG T, NDL 43
12 meters, EAD 7.8, 31 minutes, PPO2 0.75, PG W, NDL 78
O2 exposure 25%(15+10)

 

[Brandon]

Well, that's your problem... you're not giving yourself credit for the surface interval =)

After the second dive, I'm coming up with just under 40% with a 1 hour surface interval, 30% with a 1.5 hour surface interval. The credit from the surface intervals is going to keep the CNS exposure from growing very quickly, hence why RJP and others are pointing out that it's very difficult for a recreational diver to hit the limits.

-B

 

[RJP]

Well, that's your problem... you're not giving yourself credit for the surface interval =)

After the second dive, I'm coming up with just under 40% with a 1 hour surface interval, 30% with a 1.5 hour surface interval. The credit from the surface intervals is going to keep the CNS exposure from growing very quickly, hence why RJP and others are pointing out that it's very difficult for a recreational diver to hit the limits.

-B

Yup.

Plus the concern raised was for pulmonary O2 exposure, which would be tracked with OTU's, not CNS %.

 

[kaerius]

That exposure is daily limit for pulmonary oxytox, not CNS. At least that's what my instructors and PADI nitrox manual told me.

The table says Oxygen Exposure Table for Enriched Air (Nitrox)
Total exposure in 24 hours should not exceed 100%.

 

[darkstar]

Has anybody ever heard of someone toxing on recreational mixtures while diving within the recommended limits on a liveaboard? I haven't.

What I have heard, from several liveaboard operators, is that they STRONGLY recommended the use of Nitrox and that incidents of DCS have gone down since Nitrox was offered.

If they really believe that, then I think they should include it in the price. Raise the charter price if you have to, but it seems ridiculous to include cab rides, beer, Rum Cream and munchies, and then charge for something that makes diving safer. In the long run, it's probably cheaper than rushing to port with even one DCS case or dealing with a law suit that might result.

Hey Aggressor guys are you listening. I'm hoping my gas is all-in when I book in Dec.

 

[Shasta_man]

but nitrox certification still isn't 100% and those not certified will be paying for your gas.

I only use nitrox myself but the wife doesn't.

 

[darkstar]

Some people don't drink and so they are paying for my beer and Rum Cream too

Makes me feel dirty, but hey, if there's free beer I'm going to have one.

 

[RJP]

Makes me feel dirty, but hey, if there's free beer I'm going to have one.

Nothing's free...

(Except EANx if Wookie is in port!)