Nitrox on boat with air refill

[KenGordon]

I don't see that happening. Remember I am referring to NDL and you cant get a slower compartment to fill before a faster one. Of course you can fill say 3 compartments and then do a SI and have the slowest not full and the slower ones still full,,,, but you have left the NDL criteria presumed to be associated with rec diving. full means you are no longer diving NDL and the slowest fills first. No way around it.

You are ignoring that the faster compartments stop filling when 'full'. Thus the slow ones start to catch up. Just because a compartment is full does not mean it is a deco dive. It is just a modelling artefact.

Second, and probably more importantly, with repeat dives those part full slow compartments are still starting with a load.

This is why the no stop limit will be shorter on repeat dives.

After an hour a 5 minute compartment will be practically back to ambient, the slower compartments not so much.

If you spend an hour under water and an hour on the surface four times in a day you are adding more dissolved gas to those slow compartments each time. The fast ones are getting rid of nearly all of it each SI but the slow ones not.

 

[Lorenzoid]

@Lorenzoid.

Oxygen exposure tracking is important in technical and rebreather diving , NOT in open circuit recreational dives.

This is why these exposures risks are not covered in most agencies for recreational Nitrox. . . .

Is that inconsistent with what I said? You are just agreeing with me and others who have taken this position on the issue. My very first post in this thread said it's just not an issue for the OP and others doing purely recreational (OC) diving. The OP said:

I've recently got my OW and before I went for my first local boat dive to Catalina, I got Nitrox certification. . . .

Voila. Not an issue for the OP to be concerned with. Others here seem to be taking an opposing position: that some scenario within typical recreational profiles COULD be concocted in which OTU tracking becomes useful. I think it's a silly exercise. Let them have at it. The original question has been asked and answered long ago.

 

[rx7diver]

Could you please do the calculation and then show us the result?

I can't wait to see your result!!!! It won't take more than 5 mins for the calculation so please do not drag your feet. I learnt how to calculate the CNS% and OTU without any App back in 1998(IANTD Adv Nitrox). It is just simple arithmatic not any complex calculus.

I have been trying very hard to plan two consecutive recreational dives that will exceed 100% CNS but without any luck. Therefore I got nothing to show. I hope you can enlighten me on this. ... I wonder how long we have to wait for his calculation/plan?

He has to kicks out the 90mins half time to suit his calculation!! ... This is the critical element to make your calculation work!!!! You cannot arbitrary remove a known constant from your calculation in order to serve your purpose.

@Centrals: Ummm, okay.

And you are still dead wrong. I proved it to you... You manipulated ... incorrect information ... wild assumptions ... obfuscating ... the glaring proof ... kills your argument. You. Are. Wrong.

Look, I can keep trying to explain it to you, but I can't understand it for you.

That you choose to ignore even the most glaring of information simply means that you are unwilling to admit that you are wrong. That doesn't change the fact that you are wrong.

It doesn't matter. He's picking and choosing rules to follow in order to make his calculations work, and then contradicting his own made up rules to suit. ... The point is, he's using dive parameters that are outside the realm of a reasonable recreational dive, while ignoring other factors just to try and prove his point. Which, coincidentally, has been so thoroughly disproven I don't even know why he would continue posting here.

@JohnnyC: Ummm, okay.


Safe Diving,

rx7diver

 

[JohnnyC]

Disprove me rx7diver. Tell me how a 30 minute dive at a PO2 of 1.5 gives you a CNS loading of greater than 25%. I can wait. NDL is irrelevant, SAC is irrelevant, depth is irrelevant.

It's not "ummmm, okay." It's you're wrong. Admit it. I've proven why you're wrong, so prove to me why you're right. Without trying to obfuscate by adding completely irrelevant information.

 

[tursiops]

Disprove me rx7diver. Tell me how a 30 minute dive at a PO2 of 1.5 gives you a CNS loading of greater than 25%. I can wait. NDL is irrelevant, SAC is irrelevant, depth is irrelevant.

It's not "ummmm, okay." It's you're wrong. Admit it. I've proven why you're wrong, so prove to me why you're right. Without trying to obfuscate by adding completely irrelevant information.

He can't hear you; his head is in the sand.

I've tried for years to find a set of profiles that will put me over the top on O2 using recreational profiles....and I allow as many dives as you can fit in, within NDLs, not just two.
Here is a post on that from SB, http://www.scubaboard.com/forums/ad...icity-calculator-post7441100.html#post7441100.

"I've (for fun) tried using the PADI Nitrox tables to see if I can construct an NDL dive series on 32% or 36% that will hit the oxtox limits. I can sort of get there using 36%, but cannot reasonably with 32%. I was doing things like NDL dives to the MOD for 36%, normal surface intervals, then doing it again. So on dive one to 90 ft for 40 mins you pick up 30%; 1h SI lets the next 90 ft dive be for only 21 mins, so you only pick up 15% on that dive. So 3 more 21 min dives to 90 ft, with a 1h SI in between, gives another 45%, for 90% total. So, using 36%, 5 consecutive dives to 90 ft, all to max NDL, and 1h surface intervals, gets me to 90%.

Doing the same strategy with 32%, first dive is to 110 ft for 25 mins, giving 20% O2. 1h SI, second dive can only be to 110 ft for 13 mins, giving 10% O2. 7 more NDL dives like that and I'm at 100%, but I had to do 10 dives totaling 142 minutes BT plus 9h of SIs, for a LONG day!"

Note that this is using the PADI tables, which do not have any half-time for O2.
Also, the PADI tables are not recommended for such a long series of near-the-edge repetitive dives.

 

[NAM001]

I understand all that. You are telling me nothing new. I think you are arguing a point that does not happen. You are not going to get a 1 hour compartment to be full or near full with a low fast compartment while diving n the recreational diving arena. I say this because the first compartment that reaches 100% is the NDL limit no matter which compartment is controllinig. Look at DIVE NAV nitrogen loading software and you can watch it happen. Yes i agree tha if you did a tech dive and deco that left you with compartments 3,4 and 5 full and then did a rec dive that had those same full and 1 emoty and 2 partially full your position may be valid. The key is that we are not talkiing about any technical dive effect being involved only recreational dives honoring recreational limits. Also your Statement about doing a deep dive and then gong shallow causing the fast to drop while the midle compartments continue to load is not valid because althought hat is happening the middle compartments will not reach NDL.

You are ignoring that the faster compartments stop filling when 'full'. Thus the slow ones start to catch up. Just because a compartment is full does not mean it is a deco dive. It is just a modelling artefact.

Second, and probably more importantly, with repeat dives those part full slow compartments are still starting with a load.

This is why the no stop limit will be shorter on repeat dives.

After an hour a 5 minute compartment will be practically back to ambient, the slower compartments not so much.

If you spend an hour under water and an hour on the surface four times in a day you are adding more dissolved gas to those slow compartments each time. The fast ones are getting rid of nearly all of it each SI but the slow ones not.

---------- Post added November 15th, 2015 at 02:46 PM ----------

I just got to my nitrox manuals. This is what i found. It also supports what i said before. on a daily limit the exposures are added to get a daily total with no alteration for credit from SI's.
The per dive gets credit for half life reduction to allow tracking on a per dive or follow on dive levels. There are rules as stated before by another poster about required SI periods based on your per dive exposure. So if you have 2 dives that have reached say 80 percent you are required to do a manditory SI to purge before you get wet again. There is also a requirement for a daily exposure of near 100% that requires a 12 hour SI before getting wet again. There fore the 90 min half life is used on a dive to dive basis so you can have 4 dives that are building exposure points and reducing via surface intervals totaling say 150% of a per dive limit and reduced by say 90 through SI's so the next dive would start at a exposure of 60 going in. The daily exposure is recorded at 150 because that is what you accumulated for the day. The per dive limit is based on using the SI to reduce it and the DAILY is longer because there is no credit for purging alowed. When you get near the daily limit you require a 12 hour min SI. So to some extent the daily sets a limit for how many times you can max and SI youre per dive exposures. The daily time limits also assumes that you are properly using the SI's for per dive exposures as called for. Reference TDI Understanding Nitrox. If i remember correctly the advanced nitrox book does all the paper tracking .

 

[Centrals]

He can't hear you; his head is in the sand.

I've tried for years to find a set of profiles that will put me over the top on O2 using recreational profiles....and I allow as many dives as you can fit in, within NDLs, not just two.
Here is a post on that from SB, http://www.scubaboard.com/forums/ad...icity-calculator-post7441100.html#post7441100.

"I've (for fun) tried using the PADI Nitrox tables to see if I can construct an NDL dive series on 32% or 36% that will hit the oxtox limits. I can sort of get there using 36%, but cannot reasonably with 32%. I was doing things like NDL dives to the MOD for 36%, normal surface intervals, then doing it again. So on dive one to 90 ft for 40 mins you pick up 30%; 1h SI lets the next 90 ft dive be for only 21 mins, so you only pick up 15% on that dive. So 3 more 21 min dives to 90 ft, with a 1h SI in between, gives another 45%, for 90% total. So, using 36%, 5 consecutive dives to 90 ft, all to max NDL, and 1h surface intervals, gets me to 90%.

Doing the same strategy with 32%, first dive is to 110 ft for 25 mins, giving 20% O2. 1h SI, second dive can only be to 110 ft for 13 mins, giving 10% O2. 7 more NDL dives like that and I'm at 100%, but I had to do 10 dives totaling 142 minutes BT plus 9h of SIs, for a LONG day!"

Note that this is using the PADI tables, which do not have any half-time for O2.
Also, the PADI tables are not recommended for such a long series of near-the-edge repetitive dives.

You have to do several dives to approach the limit but NOT on TWO dives as suggested.

 

[NAM001]

I like this post. What you say only makes sense. No agency is going to offer a class that they know a bunch of nuts are going to take and end up hurt. It has to be that the limits are very difficult to exceed when staying with in ndl limits. I have a spread sheet I tried this and it too something like 8+ dives to get to the daily cns of out limit. And then had to use upward of 40% nitrox to do it. You have come to the same conclusions as it appears. My only limitation on the spreadsheet was not to use times that exceeded NDL. I agree with you that anyone can use 1 hour dives at 100 ft to force reaching limits, but that is no longer rec diving.

He can't hear you; his head is in the sand.

I've tried for years to find a set of profiles that will put me over the top on O2 using recreational profiles....and I allow as many dives as you can fit in, within NDLs, not just two.
Here is a post on that from SB, http://www.scubaboard.com/forums/ad...icity-calculator-post7441100.html#post7441100.

"I've (for fun) tried using the PADI Nitrox tables to see if I can construct an NDL dive series on 32% or 36% that will hit the oxtox limits. I can sort of get there using 36%, but cannot reasonably with 32%. I was doing things like NDL dives to the MOD for 36%, normal surface intervals, then doing it again. So on dive one to 90 ft for 40 mins you pick up 30%; 1h SI lets the next 90 ft dive be for only 21 mins, so you only pick up 15% on that dive. So 3 more 21 min dives to 90 ft, with a 1h SI in between, gives another 45%, for 90% total. So, using 36%, 5 consecutive dives to 90 ft, all to max NDL, and 1h surface intervals, gets me to 90%.

Doing the same strategy with 32%, first dive is to 110 ft for 25 mins, giving 20% O2. 1h SI, second dive can only be to 110 ft for 13 mins, giving 10% O2. 7 more NDL dives like that and I'm at 100%, but I had to do 10 dives totaling 142 minutes BT plus 9h of SIs, for a LONG day!"

Note that this is using the PADI tables, which do not have any half-time for O2.
Also, the PADI tables are not recommended for such a long series of near-the-edge repetitive dives.

 

[kelemvor]

There are no stupid questions, only stupid answers.

Clearly you've never had a job doing technical support.

 

[stuartv]

I was reading Staying Alive, a most excellent book by Steve Lewis, today at lunch and I was reminded of this thread. From the book:

Many divers believe that when they do pure sport diving within recreational limits, it's hard to exceed the daily limits. It is not.

Steve Lewis is also a SB member, I believe. Shame he hasn't chimed in here.