Nitrox vs Air

[emelotto]

In reality, your best bet is to do one of two thing. The first and best choice is to dive nitrox. It will give you everything you asked for. The second option is to buy a computer with a different deco model. (IE more liberal).

Mike

Cavediver, you told me what I wanted at the end....actually, I needed to put some ideas in a way to provoque discussion, but I guess the right thing to do is to do what you suggest in the middle of a dive sequence.

For instance, to dive the 3 first dives with air and the 4th with 32 ean, than maybe intercalate 2 air and a EAN. We also might extend a little bit surface interval (1:30h at least) and when using Suunto, extremely care with quick ascents, because RGBM penalizes you a lot with those ascents.

 

[emelotto]

If we assume that we can't prove that a more liberal computer will drives you bent, how can we manage that? Because if you can prove...I guess we could see a lot of prosecutes against this factorys.

I have no idea what you mean by this.

Walter, DA got the general idea, and sorry about my bad english. The point above is the folowing: Imagine that we could prove that Oceanics algorithm is wrong and people who use Oceanics computer are starting to be bent. As we do against cigarretes, we could take Oceanics to the court and say...I got bent because you put my life at risk.
If I discover some brand is being taken to the court, I wouldn't buy it's computer anymore.

So,

And finally, if you are using a computer more liberal than mine, we do exactly the same profile and at the end my computer asks by 20minutes deco and yours asks 10min, who will be bent?

At the case above, if we skip deco with 10 min, what is the chance to get bent. (please not consider health and shape conditions, just in theory).

Anyway, as I said before...I am going to dive Nitrox in the middle of a dive sequence larger than 4 dives.

 

[emelotto]

May I change a little bit the focus of this discussion to ask other thing about Nitrox...

Here in Brazil we have a paradise called "Fernando de Noronha". It is a island an our flight far from the shore.

There is a war ship sunk at 63m, but usually we go to maximum 53m. Sometimes has current, but you descent in a rope and water is 40-50m visibility and 27°C.

The point is that they asks you to have a nitrox certification and charges you about USD200, but when you dive, you do 15min at the bottom with air and ascend till 6m when the DM gives you a pure O2 from his 15l cilinder.

What do you think about this?

 

[LavaSurfer]

May I change a little bit the focus of this discussion to ask other thing about Nitrox...

Here in Brazil we have a paradise called "Fernando de Noronha". It is a island an our flight far from the shore.

There is a war ship sunk at 63m, but usually we go to maximum 53m. Sometimes has current, but you descent in a rope and water is 40-50m visibility and 27°C.

The point is that they asks you to have a nitrox certification and charges you about USD200, but when you dive, you do 15min at the bottom with air and ascend till 6m when the DM gives you a pure O2 from his 15l cilinder.

What do you think about this?

Below is what Vplanner has to say.
How many people get bent?

I have been following this thread and have to ask. Why don't you just follow some simple rules like tables?
You seem to have this wish to cheat the system.
In an earlier thead you stated you would dive EAN in the middle of a series of dives.
WHATS THE POINT?
Why not just dive Air within its limits and EAN within its limits?
And use each when appropriate?

Here is your answer of what I and vplanner think.
In short, its a DECO dive and you need to treat it as such.

Decompression model: VPM - B
DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 0m
Conservatism = + 2
Dec to 53m (3) Air 15m/min descent.
Level 53m 11:28 (15) Air 1.31 ppO2, 53m ead
Asc to 24m (18) Air -9m/min ascent.
Stop at 24m 0:47 (19) Air 0.71 ppO2, 24m ead
Stop at 21m 2:00 (21) Air 0.65 ppO2, 21m ead
Stop at 18m 2:00 (23) Air 0.59 ppO2, 18m ead
Stop at 15m 2:00 (25) Air 0.52 ppO2, 15m ead
Stop at 12m 4:00 (29) Air 0.46 ppO2, 12m ead
Stop at 9m 5:00 (34) Air 0.40 ppO2, 9m ead
Stop at 6m 8:00 (42) Air 0.34 ppO2, 6m ead
Stop at 3m 14:00 (56) Air 0.27 ppO2, 3m ead
Surface (56) Air -9m/min ascent.
Off gassing starts at 33.6m
OTU's this dive: 25
CNS Total: 9.7%
111.9 cu ft Air
111.9 cu ft TOTAL

Diving Doubles and draining them? ...
Sounds like a load of BS to me

 

[emelotto]

Below is what Vplanner has to say.
How many people get bent?

I have been following this thread and have to ask. Why don't you just follow some simple rules like tables?
You seem to have this wish to cheat the system....

LavaSurfer, maybe I can explain better what I want to say.
Sorry but I don`t want cheat the system, but understand why I need do some things and not just believe the tables and/or computers are strictly right.

[In an earlier thead you stated you would dive EAN in the middle of a series of dives.
WHATS THE POINT?

The point is the following : when your are diving a entire week, twice a day, you never become completely out of micro bubbles and the computers penalize you saying you are saturated to start the next dive. If you, in the middle, dive with EAN32 or 36, you will help your body eliminate the micro bubble and your computer will see that. So at the next day, you will probably start the dive completely off gassed. If somebody got the point and has a better english than mine, please explain with more details.

About the second part, I forgot that we made a Stop at 18m by 3 min.

But what I want to know from you guys, is what do you thing doing this 53m dive with air and to finish with 100% O2 at 6m. Off course is a deco dive, but should we use Trimix? Should we use EAN 32 from 20m? This is the kind of info I would like to see.

 

[LavaSurfer]

The point is the following : when your are diving a entire week, twice a day, you never become completely out of micro bubbles and the computers penalize you saying you are saturated to start the next dive. If you, in the middle, dive with EAN32 or 36, you will help your body eliminate the micro bubble and your computer will see that. So at the next day, you will probably start the dive completely off gassed. If somebody got the point and has a better english than mine, please explain with more details.

I understand your point but don't get the motivation.
Why not just dive EAN all the time and reduce even more?
Making it so complicated just turns simplicity into disaster.

About the second part, I forgot that we made a Stop at 18m by 3 min.
But what I want to know from you guys, is what do you thing doing this 53m dive with air and to finish with 100% O2 at 6m. Off course is a deco dive, but should we use Trimix? Should we use EAN 32 from 20m? This is the kind of info I would like to see.

Below is the same dive with EAN32 as a DECO Gas
Still a two tank dive.
100% O2 at 6M is about 1.5 PPO2
You are all sharing the 02?
how could there be enough?
It just seams like a disaster waiting to happen.

Here is a plan using EAN32 for DECO
Decompression model: VPM - B
DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 0m
Conservatism = + 2
Dec to 53m (3) Air 15m/min descent.
Level 53m 11:28 (15) Air 1.31 ppO2, 53m ead
Asc to 36m (16) Air -9m/min ascent.
Asc to 24m (18) Nitrox 32 -9m/min ascent.
Stop at 24m 0:47 (19) Nitrox 32 1.08 ppO2, 19m ead
Stop at 21m 1:00 (20) Nitrox 32 0.99 ppO2, 17m ead
Stop at 18m 1:00 (21) Nitrox 32 0.89 ppO2, 14m ead
Stop at 15m 2:00 (23) Nitrox 32 0.80 ppO2, 12m ead
Stop at 12m 3:00 (26) Nitrox 32 0.70 ppO2, 9m ead
Stop at 9m 4:00 (30) Nitrox 32 0.61 ppO2, 6m ead
Stop at 6m 5:00 (35) Nitrox 32 0.51 ppO2, 4m ead
Stop at 3m 10:00 (45) Nitrox 32 0.42 ppO2, 1m ead
Surface (45) Nitrox 32 -9m/min ascent.
Off gassing starts at 33.6m
OTU's this dive: 31
CNS Total: 12.2%
66.4 cu ft Air
33.6 cu ft Nitrox 32
99.9 cu ft TOTAL


Here is a plan as you dive it now
Decompression model: VPM - B
DIVE PLAN
Surface interval = 1 day 0 hr 0 min.
Elevation = 0m
Conservatism = + 2
Dec to 53m (3) Air 15m/min descent.
Level 53m 11:28 (15) Air 1.31 ppO2, 53m ead
Asc to 21m (18) Air -9m/min ascent.
Stop at 21m 2:27 (21) Air 0.65 ppO2, 21m ead
Level 18m 3:00 (24) Air 0.59 ppO2, 18m ead
Asc to 12m (25) Air -9m/min ascent.
Stop at 12m 4:00 (29) Air 0.46 ppO2, 12m ead
Stop at 9m 5:00 (34) Air 0.40 ppO2, 9m ead
Stop at 6m 8:00 (42) Air 0.34 ppO2, 6m ead
Stop at 3m 14:00 (56) Air 0.27 ppO2, 3m ead
Surface (56) Air -9m/min ascent.
NOTE: This Multi Level dive requires intermediate deco stops between levels.
OTU's this dive: 25
CNS Total: 9.6%
113.7 cu ft Air
113.7 cu ft TOTAL

Either way this dive required several DECO stops and doubles

 

[ianr33]

Not at all. That is exactly how they're supposed to be used.


No, no, no, no, no!! Yellow = caution. Green = Safe.

How long does it take to enter the Green Zone when you have 10 min left on tables? Another 10 min at least, I bet.

Please repeat Drivers Ed course before driving with stop lights.

Don look carefully at what I wrote. The word safe is in quotation marks. i.e.safe is not to be taken literally.

In this example I am following tables.The computer is a BACKUP

Just because your computer is in the green does not mean that it is SAFE to exit the water,you have not suddenly passed a well defined line between YELLOW (unsafe) and GREEN (safe) You will learn about this when you take technical classes

Please repeat reading comprehension 101

 

[DandyDon]

Don look carefully at what I wrote. The word safe is in quotation marks. i.e.safe is not to be taken literally.

In this example I am following tables.The computer is a BACKUP

Just because your computer is in the green does not mean that it is SAFE to exit the water,you have not suddenly passed a well defined line between YELLOW (unsafe) and GREEN (safe) You will learn about this when you take technical classes

Please repeat reading comprehension 101

Okee dokee - I kinda' mistyped what I was trying to say. Thanks for not getting bent over it.

So, when you have 10 min of deco left, and the Oceanic goes into the yellow, how long does it take to go into the green...?

 

[miketsp]

Here is your answer of what I and vplanner think.
In short, its a DECO dive and you need to treat it as such.

111.9 cu ft

Diving Doubles and draining them? ...
Sounds like a load of BS to me

There's something here that doesn't stack up.
What SAC did you calculate on?

I ran my own calculation for the profile you gave at a SAC of 13liter/min (given that my average is 12 and would probably be less on this dive because it's a dive which requires almost no physical effort) and came up with only 79 cu ft?

 

[DA Aquamaster]

So, when you have 10 min of deco left, and the Oceanic goes into the yellow, how long does it take to go into the green...?

That's a great point point. If a diver is on their first deep and relatively short dive, the nitrogen bar graph will drop pretty fast as it represents the loading of the most critical compartment which in this case will be the short half life compartments that are most quickly loaded on a deep dive. In this case a few minutes at 15-20 ft makes a huge difference in dropping you out of the yellow and into the green as these compartments also off gas relatively quickly.

However if you have done a few dives already or if the first dive was a long one at a middle depth around 60-70 ft, the bar graph is again going to represent the controlling compartment that is most heavily loaded. Initially this will be the same short half lifed compartment, but as soon as it clears other slower compartments will assume that role in succession and it can take a very long time to get the nitrogen loading bar graph to drop by more than a bar or two. You may not have the gas to get back in the green, so you are not going to want to go there in the first place if you want to exit the water in the green.