02 on non deco dives

[Scuba_Steve]

Ah..the computer factor, weight, hydration, improper ascent tecnhniques.......not for this thread BJet

Getting "bent" within NDL's are most usually other factors than the time at depth....see the above sentence for examples, and again is not what the original poster asked about.

Also, to be on topic, one thing I have forgotten to mention at least 3 times (my bad), if the original poster wants to be "safer" within the NDL aspect, there's a built-in factor by using Nitrox already/ Lets assuem for arguement's sake that the NDL, whatever that imaginary number is, was used along with the EAD calc.

As the "tables" use air all the way up, even though you've used the EAD calc to get you B/T (if you care to do it this way). you are now doing your rolling "deco" stop using a higher FO2 and therefore are adding an additional benefit by using Nitrox as your backgas, that the tables aren't actually factoring in....an added bonus.

Or at least, so the story goes

Steve

 

[mempilot]

For keeping it basic, it comes down to a few things: time to ongass N2, O2 clock, and PP02. Why screw around with the tables at all to be more safe? Just dive less time on a more conservative PO2 and save yourself from OXTOX and N2 at the same time. Why manipulate tables, carry different mixes, and complicate a dive that is being planned as recreational? Otherwise, do the little bit of extra training, it isn't hard, and plan it as a multigas dive.

 

[Scuba_Steve]

For keeping it basic, it comes down to a few things: time to ongass N2, O2 clock, and PP02. Why screw around with the tables at all to be more safe? Just dive less time on a more conservative PO2 and save yourself from OXTOX and N2 at the same time. Why manipulate tables, carry different mixes, and complicate a dive that is being planned as recreational? Otherwise, do the little bit of extra training, it isn't hard, and plan it as a multigas dive.

What he said

Nothing better than a relaxing NDL on Nitrox with the wife. No monkey business, no extra, needless gas switching exercise to complicate matters. Simply not needed in this type of diving.

Resist the urge (And it is an urge) to complicate needlessly.

K.I.S.S.

 

[DepartureDiver]

Sorry for the length here, but hopefully it will be worthwhile even if not all points are agreed with.

I really am stunned when I hear people criticize others in this manner. As you obviously know, decompression routines are NOT A RACE. There are NO awards for getting back to the boat sooner than someone else. To use that as a point of criticism is, in a word, STUPID. :nonono:

Yes. We've heard it many times from several sources. Most either felt the need to be viewed as all knowledgeable or were advocating their own decompression procedures. We were even told that staying underwater even creates its own hazards. A big discussion even wound up here on the Board awhile back in another forum. We were diving in unknown areas (like all tech dives) to 400' at altitude. Our ascent curve was more conservative than most and with longer stops at 20'. As you pointed out, too many believe that decompression and dive modeling is understood - which it is really not. So diving to what one says or a table says in nonsense if you want to be proactive in avoiding a hit.

Why screw around with the tables at all to be more safe? Just dive less time on a more conservative PO2 and save yourself from OXTOX and N2 at the same time

No one has given procedures to screw with the tables … but, not to knock your valid suggestion, isn’t your suggestion the same thing?

Getting "bent" within NDL's are most usually other factors than the time at depth.

I disagree. To always look for a reason and then say a diver blew it completely dismissed the point that a bend occurred. The individual thresholds for each diver is vastly different. To assume all divers will bend within minutes of the limits of the tables is simply not correct.

if the original poster wants to be "safer" within the NDL aspect, there's a built-in factor by using Nitrox already

Yes, but if using the air lmit you mus still calculate your CNS level … an added step of complexity … but an easy one.

Lets assuem for arguement's sake that the NDL, whatever that imaginary number is, was used along with the EAD calc. . . . you are now doing your rolling "deco" stop using a higher FO2 and therefore are adding an additional benefit by using Nitrox as your backgas, that the tables aren't actually factoring in....an added bonus.

The off gassing during the ascent on nitrox will be a minimal difference, but using nitrox at a safety stop is good … which was the original point.

I also think we need to go back to the concept that all dives are deco dives and that a stop is to promote off gassing before surfacing. I’m reading that people suggest reducing bottom time to reduce the nitrogen load. But a large amount of time needs to be reduced to get a small cutback in the nitrogen load. For arguments sake, I will assume that divers want more than a 10% decrease from the allowed maximum since a 10% decrease is small. So let’s pick a 20% decrease in nitrogen load. To get this decrease, the times need to be cut back by almost 40%. A dive to 130’ with an NDL of 10 needs to be reduced to 6 minutes. Likewise a dive to 80’ with an NDL of 30 min. needs to be reduced to 19 min and a dive to 60’ with an NDL of 55 min needs to be reduced to 35 minutes. So reducing the times by a few minutes does very little good considering that each diver’s own personal threshold is vastly different. I don’t know of many that are willing to do this or at least most don’t as seen by divers pushing their computers. So the next step is to decompress efficiently even when within the NDL’s. This is done by safety stops, etc. But a 5 minute safety stop after 55 minutes at 60’ only reduces the nitrogen load by 7% if using a pure half-time model and when using a bubble model, it is probably more like 3%. So back to the question about doing proper decompression during a recreational dive to achieve a decent margin of safety . . . one way is to significantly cut back the time at depth and another way is to use a stage gas and do the one extra calculation of the CNS contribution from the stage gas. I just don’t see this as complicated for those that want to do it and obviously have taken the class. It is a great benefit to off-gassing.

One last point is that the nitrogen load after one dive obviously affects the next dive in the way of determining RN. Without mentioning names, some tables assume a rapid release of nitrogen over a short period of time and the greater the nitrogen load the faster the initial RN groups are dropped. Likewise computers can also assume fast off gassing. The problem is that the greater the nitrogen load, the greater the bubbling will be. Once bubbles form (as they will after virtually all dives) the off gassing is severely hindered. Since the gas is in a bubble and not in solution anymore, the driving force for nitrogen elimination is load, i.e. the bubble must now be reabsorbed. Since many tables and computers assume a pure half-time off gassing, they are calculating RN’s that are less than they should be. So again, it is more beneficial to avoid the high nitrogen load in the first place.

 

[BigJetDriver]

Ah..the computer factor, weight, hydration, improper ascent tecnhniques.......not for this thread BJet

Getting "bent" within NDL's are most usually other factors than the time at depth....see the above sentence for examples, and again is not what the original poster asked about.

Steve

Steve,

You are right. It's not what the original poster needed to know about. It's just kind of a favorite soap-box with me. Sorry!

 

[Scuba_Steve]

Steve,

You are right. It's not what the original poster needed to know about. It's just kind of a favorite soap-box with me. Sorry!

No probs with me bud. I just know that I tend to get off topic lots, and have tried for abotu 2 weeks now not to do so....with marginal success at this point.

As to the CNS dispute above.......CNS is a moot point while diving Nitrox on Rec dives when diving, say EAN32.

Add it up if you like, but it's a lesson not worth the exercise more than once!

You're simply not going to get enough O2 in you to worry about unless you're actually trying to do so, which I don't think is possible with a PO2 of 1.4 or less (The reason for only using EAN32 throughout the range of Rec dives) and even multiple dives per day.

Check it out for yourselves! Do 3-4 dives a day, on EAN32, Rec NDL's in play, do it for 5 days.......keep the scenario real, and try not to force a conclusion either way. (The first guy with SI's of 2 minutes get's a weenie punch! LOL)

Waste of time doing the calcs more than once

I like K.I.S.S. diving myself

See ya guys (B/Jet, was this off topic too??) Maybe.

Steve

 

[Scuba_Steve]

I disagree. To always look for a reason and then say a diver blew it completely dismissed the point that a bend occurred. The individual thresholds for each diver is vastly different. To assume all divers will bend within minutes of the limits of the tables is simply not correct.

I can'r imagine why you think I said this, I've re-read it, and didn't get anything of the sort.

I in fact will be the first to tell you or anybody that there's no "Magic number" were a hit will not occur.

What I am simply saying is quite the opposite of what you just said I said.

What I AM saying is Time and Depth are usually NOT the reason why a diver gets an "undesereved hit". (As in, stayed within the NDL of thier depth).

It usually those other reasons, which I noted earlier in that post.

Please also see my last post why Calculating CNS loading is rediculous as well while on NDL's with a moderate PO2 limit.

For the record, I only now just ran a scenario to prove by otherwise bold stance on CNS limits and Rec dives.

Here's the scenario:

110ft B/Time 20mins, EAN32

It took 7 dives, with a 30min SI to get to even 50% CNS loading.

It shouild be quite clear that this is a serious dive day!

No-one would realistically make 7 110ft dives with 30min inbetween each and every one of them. Even if one did, the result is about 50% CNS loading.

It's after running scenarios like this, that one eventualy gets the gut knowledge when they see somethign like Mem's accidental posting of incorrect CNS infoa few pages back. (Not blaming you directly dude, it's what the puter told you!!).

I knew instantly it was just plain wrong. Didn't know why, but I did suspect some non-credit of SI intervals as the cause. But whatever, it just stunk for any reason!

To expect the gut-ballpark understanding from a newly minted Nitrox diver may be a bit much, but I certainly would expect someone that has done enough dives with Nitrox to get that "ballpark idea" without having to figure it out. Heaven help the poor guy that blindly followed an incorrect calc based on something funny going on within their calcs (Or the puter's), without knowing instinctively that it just isn't adding up.

Have a good one gents

Steve

 

[BigJetDriver]

See ya guys (B/Jet, was this off topic too??) Maybe.
Steve

Dunno, these things tend to mutate more than the aliens in a bad sci-fi movie as they go along anyway!

Cheers!

Rob

 

[DepartureDiver]

I in fact will be the first to tell you or anybody that there's no "Magic number" were a hit will not occur.

What I AM saying is Time and Depth are usually NOT the reason why a diver gets an "undesereved hit". (As in, stayed within the NDL of thier depth).

Sorry, I'm being dense here and maybe I am missing your point. Mine was that since there are no magic numbers, some undeserved hits (i.e. within the NDL's) are from one's own limits not being within the average range. Therefore the hit was related to time and depth since that diver's personal limits were exceeded even though they were within the NDL's.

Please also see my last post why Calculating CNS loading is rediculous as well while on NDL's with a moderate PO2 limit.

I completely agree. I also stated the if keeping the PPO's to 1.3 or less, any addition from a stage gas would be small.

Dunno, these things tend to mutate more than the aliens in a bad sci-fi movie as they go along anyway!

but even off track B movies are fun . . . plus I got another 1/2 star for all these posts.

 

[Scuba_Steve]

but even off track B movies are fun . . . plus I got another 1/2 star for all these posts.

Damn, I haven't been tracking my "Star" loading through this thread