Is Deep Air / Light Deco (bounce?) Discussible on ScubaBoard?

[DiveNav]

.....6. What protocols do you use for determining a decompression profile? U.S. Navy Standard Air Tables....

mmhhhhh ..... so, are we then saying the a good portion of recreational - multilevels - dives are indeed deco dives? ....

Example, max depth 100ft with only few minutes there, then ascend leisurely following the reef profile for a total dive time of 40 minutes...... like the profile in the image.

According to computer X (or Y, or Z) the diver is good to go ..... according to the tables the diver is dead

​

Alberto (aka eDiver)

 

[Thalassamania]

No, I'm saying that when I plan a dive of this sort for both the standard and contingency packages I use the U.S. Navy Standard Air Tables. Computers have a whole different set of definitions, and here we are talking about rather quick, rather square, dives that are well suited to table use.

 

[MauiScubaSteve]

Well, there's very little point setting a conservative mode on a recreational dive, if you're not going to adhere to the NDL anyway.

You either dive conservatively, or you dive aggressively. People set the conservative status because they want to dive prudently and/or they acknowledge specific factors that may otherwise predispose them to DCS. Going into deco is probably not the best strategy if a diver is concerned about their predisposition to DCS.

Why would anyone who wanted to dive aggressively then put their computer into a more conservative mode? To win petty arguments on an internet forum?

Well, let's talk more about this ...

I've been reading my computer manual ...

Even not finding the 100% or 50% rgbm setting, it is most likely factory, 100%, and I can adjust the "normal, "1st conservative" and "2nd conservative", so setting it more, and more, conservative would mean longer, and longer, ASC time upon exit from Devil's Throat. Then I might hustle up to shallower reef (even a little above), for a little longer off gassing because I'm using air slower. Where as, with a non conservative set Oceanic Veo (I only speak Suunto ), on other arm, I could slowly ascend the wall (?) until time showing is 0, ride the 0 up to the shallow reef, where I incur a couple minutes mandatory (5 minute stop) and then have just enough air for indicated stop (end 300 psi).

Which is a safer way to dive Devil's Throat?

I plan to dive Devil's Throat ...

 

[DevonDiver]

Even not finding the 100% or 50% rgbm setting, it is most likely factory, 100%, and I can adjust the "normal, "1st conservative" and "2nd conservative", so setting it more, and more, conservative would mean longer, and longer, ASC time upon exit from Devil's Throat. Then I might hustle up to shallower reef (even a little above), for a little longer off gassing because I'm using air slower. Where as, with a non conservative set Oceanic Veo (I only speak Suunto ), on other arm, I could slowly ascend the wall (?) until time showing is 0, ride the 0 up to the shallow reef, where I incur a couple minutes mandatory (5 minute stop) and then have just enough air for indicated stop (end 300 psi).

Not exactly sure what you're saying. Can you re-phrase for clarity?

A conservative setting is going to have a primary impact on your dive: bottom time.

Dive Nav mentioned that deco was relative. On the same computer, for the same bottom time, a dive might be deco or not deco depending upon the setting of the computer. His point being (I assume?) that the same dive is done, the same nitrogen absorbed, the same physiological impact for the diver. Therefore, why stress about 'light' deco?

My response was that there'd be no logic into setting a conservative mode... then riding the hell out of it...and/or pushing it into deco. If it was your intention to dive aggressively, then just use the most aggressive mode available. You still have the option to conduct a longer shallow stop if you desire. You don't need to force your computer into deco mode in order to do a longer safety stop.

Either way, your bottom time is your bottom time. Your ascent time is your ascent time. Your stop time is your stop time.

Going into deco mode opens up a lot more risks - namely, that the 'average' diver won't know where to draw the line on that 'light' deco. It'd depend on their past diving profiles, their residual nitrogen, the computer algorithm, ascent profiles...and a host of DCI precursors that they may, or may not, have.

Given that the 'average' (or in fact, the vast majority of) divers don't have any training or education about such issues... the prudent thing is to -quite simply- not​ go into deco.

For those that do have the training and education... well, there's no problem. We call it tech diving. We talk about it here.

 

[MauiScubaSteve]

Please; I hope you are just playing your part.

You can easily find the pdf Suunto Viper manual and scroll down to Decompression. I perviously posted the definition to ASC time so go back and re-read that post.

I find it possible to believe that there is a chance that in the stock setting (100%rgbm/normal) I might exit Devil's Throat with no ASC time, near the end of my ndl. The least conservative setting seems to be 50%rgbm/normal (if my computer can), which would theoretically be more bottom time at 135' when I exit. Using 100%/1st conservative, I might expect some ASC time at exit; 100%/2nd conservative should yield even more ASC time at exit.

Knowing my time to surface @ 33 fpm I subtract to find my stop; computer assumes ascent @33 fpm. At 132' that ascent time is 4 min. If I use my imaginary least conservative exit time from above as 3 min, my highest level of certification (max 10 minute stop) allows me to stay until ASC time reaches 14, as long as I do average 33 fpm on ascent. AFAIU, my formal training does not consider half depth stops.

The computer will ring bells if I exceed 33 fpm, and may lock up if I exceed 55 fpm for over 3 min, but I think from reading that quicker than 33 fpm to 66 feet violations will be resolved as long as entire stop is completed, so air permitting, staying to 15 min ASC @ 132' is going to be damn close to 10 min stop.

From what I've read, Suunto's are among the most conservative pdc's so I was postulating that the Oceanic Veo might show more than 3 min ndl upon exit, although the difference may be small on first dive with clear history. So following ndl diving rules I could slowly ascend until the ndl time reaches 0-1 min and then ascend fast enough to keep the ndl time between 0-2 minutes, then at top of reef (60'?), air permitting, I might keep diving until I had a 5 min stop showing (however Oceanic shows mandatory 5 min stop ).

Same exit of overhead time, different options as far as finishing profile; for an AOW Diver with deep diving experience some might say that on the "Oceanic profile", they only violated their training/experience by 2 minutes / 3-5 feet.

I chose the settings based on my risk factors and then dive 5 feet deeper than the training dives limit of my certification, but with an AL80, air may be the decider.

 

[dumpsterDiver]

Please; I hope you are just playing your part.

You can easily find the pdf Suunto Viper manual and scroll down to Decompression. I perviously posted the definition to ASC time so go back and re-read that post.

I find it possible to believe that there is a chance that in the stock setting (100%rgbm/normal) I might exit Devil's Throat with no ASC time, near the end of my ndl. The least conservative setting seems to be 50%rgbm/normal (if my computer can), which would theoretically be more bottom time at 135' when I exit. Using 100%/1st conservative, I might expect some ASC time at exit; 100%/2nd conservative should yield even more ASC time at exit.

Knowing my time to surface @ 33 fpm I subtract to find my stop; computer assumes ascent @33 fpm. At 132' that ascent time is 4 min. If I use my imaginary least conservative exit time from above as 3 min, my highest level of certification (max 10 minute stop) allows me to stay until ASC time reaches 14, as long as I do average 33 fpm on ascent. AFAIU, my formal training does not consider half depth stops.

The computer will ring bells if I exceed 33 fpm, and may lock up if I exceed 55 fpm for over 3 min, but I think from reading that quicker than 33 fpm to 66 feet violations will be resolved as long as entire stop is completed, so air permitting, staying to 15 min ASC @ 132' is going to be damn close to 10 min stop.

From what I've read, Suunto's are among the most conservative pdc's so I was postulating that the Oceanic Veo might show more than 3 min ndl upon exit, although the difference may be small on first dive with clear history. So following ndl diving rules I could slowly ascend until the ndl time reaches 0-1 min and then ascend fast enough to keep the ndl time between 0-2 minutes, then at top of reef (60'?), air permitting, I might keep diving until I had a 5 min stop showing (however Oceanic shows mandatory 5 min stop ).

Same exit of overhead time, different options as far as finishing profile; for an AOW Diver with deep diving experience some might say that on the "Oceanic profile", they only violated their training/experience by 2 minutes / 3-5 feet.

I chose the settings based on my risk factors and then dive 5 feet deeper than the training dives limit of my certification, but with an AL80, air may be the decider.

Not sure I understand all that stuff, but if I were doing that kind of dive, I would definitely incorporate a deep stop at around 50 feet for maybe 2 minutes... even if the computer penalizes me and gives me more deco.

Not sure what riding the zero is either? Is that coming up with no deco on the computer and then stopping at many depths and then staying there until the no deco time expires and then move up 20 feet and hang out until you reach the NDL at that depth? To me, that sounds very aggressive... Maybe it is over simplistic, but you would be loading up each compartment to the max.

For a quick bounce dive you want to come up resoanbly fast, especailly from the deeper portion, I like to stop at 50 or so and then move on up to just less than 30 feet and try to clear the deco and then move slowly up from there in a couple minutes. Hanging around at 80, 60 and maybe 50 for as long as possible is not what i would do... if that is what you are asking?

 

[MXGratefulDiver]

I'm in agreement with DD on the deep stop ... you want to take care of those fast tissues, because if you're pushing the limits and you guess wrong, a fast tissue hit is a lot harder to deal with than a slow tissue hit.

I've done similar experiments to what Halemano describes ... strapping a Suunto Vytec and Oceanic Versa Pro side-by-side to see how they would handle an aggressive profile. In my case, my max depth was about 115, and I stayed there long enough to run the Oceanic down to zero NDL ... the Suunto at that point was showing 26 minutes of deco obligation ... :shocked2:

Making my way up to 60 fsw, I stayed there for 5 minutes. The Oceanic went about 4 minutes into deco while the Suunto started reducing minutes. I plateaued again at about 40 fsw for about 10 minutes. The Oceanic remained at the 4 minutes deco, while the Suunto reduced to about 12 minutes. By the time I got to 20 feet, the Oceanic indicated I was clear to ascend while the Suunto said I had a mandatory 8-minute obligation. I decided to hang out for about 15 minutes, mainly because I'm an old dude, and had plenty of gas with me ... I was diving a single HP130 and slinging an AL40.

The "moral of the story" for me is that if you're going to depend on a computer to tell you how to shape your profile, you should understand the assumptions of its algorithm. The Oceanic was using a more or less standard Buhlmann model, which doesn't credit offgassing fast tissues at deeper depths ... hence penalizes you for making "deep stops". The Suunto, on the other hand, with its modified RGBM algorithm, credits you for reduced pressures that allow offgassing to begin at deeper depths. In effect, it is not what's going on inside your body that determines how much deco time you have to honor ... it's what assumptions the computer algorithm is making when doing the math. If you're going to do this, it's important to have at least a basic understanding of what those assumptions are ... and what risk factors apply to you that might make it prudent for you to "pad" the numbers the computer is displaying. Knowing this ... even at a broad, basic level ... helps you make decisions that may keep you from taking an "undeserved" hit ... and, more importantly, might help you realize the importance of taking more gas than you think you might need.

And finally, thank you all for helping to put this train back on the rails ...

... Bob (Grateful Diver)

 

[boulderjohn]

I'll make a stab at John's questions:

Thanks. I hope others will do the same.

To my way of thinking, the only concern I see with those parameters is the old narcosis issue, and in the right situation, that would not unduly concern me either. I have personally been within very similar parameters diving air when helium was not available and before I was certified for it. I have gone to 181 feet in a hold on the San Francisco Maru in Chuuk while maintaining safety factors such as you describe for each item on the list. I know a UTD instructor who recently went over 180 feet on air with a single AL 80 on his back and another slung under his arm, again using protocols similar to yours for safety. (UTD is quite insistent that all diving below 100 feet be done with a standard trimix.) He was in Fiji with no possibility of helium and the proposed dive was quite inviting.

I have only minor qualms related to narcosis when discussing deep air, as long as all other safety factors are well considered.

Let's contrast this with the deep air episodes that sparked this recent debate. The Cozumel incident involved three divers heading to 300 feet on single tanks, getting narced, going to 400, and running out of air on ascent. In Louisiana, two divers decided to look for large grouper below 200 feet on single AL 80s, and one of them never returned. In the discussion that followed, most people said these practices were unsafe, but VDGM and some others seemed to argue that there was nothing inherently wrong it, that those dives were as safe as any other, and that sometimes you just die on scuba. The decision to dive deep on air with a single tank was not a relevant factor in those deaths. VDGM then went on a crusade, injecting those views into several threads and starting several of his own threads on the topic. He was clearly advocating it.

I am just trying to get a handle on what people are talking about. I don't think we can have a discussion about it until we know what we are talking about.

 

[DevonDiver]

I'll have a crack at John's questions too:

1. What depth limits do you have for diving on air?

55m/180ft... planned and equipped as a technical dive.
I've dove much deeper than that on air before, but I don't think I would do the same again now.

2. I have read over an over again in this thread that it is not for beginners. How much experience does a basic OW diver need to have, and what kind of experience should that be?

A basic OW course doesn't provide any training, knowledge or procedures for deep diving (below 30m). I believe that a specific skill-set and knowledge-base is required for deep diving. Deep air should be treated as a specialised gas - the properties of that gas have changed, compared to shallow water - so it requires specific preparation in the same way that nitrox or trimix would.

3. How does a diver determine how much air is needed for a dive?

Here is what I teach & use: Scuba Diving Tips - Gas Management WorkshopScuba Tech Philippines
Note: This isn't taught on any mainstream scuba course at recreational level. A diver shouldn't be doing deep dives without the capacity and discipline to go through these steps as a part of dive planning. It's an example of why most recreational divers shouldn't consider deep diving, let alone novice/inexperienced OW trained divers.

4. At what level of remaining gas should a diver begin an ascent?

As dictated by their gas planning. For general recreational dives, a 'rock bottom' is necessary to ensure that the diver can return to the surface whilst air-sharing with their buddy, completing all stops and ascending at a safe rate. For deeper dives, a larger contingency is necessary because there is a danger that an unplanned delay could lead to deco obligation. Rule of Thirds may be deemed appropriate for this.

5. Is there any need for redundancy? Is one tank enough?

For deep diving, potential unplanned delays leading to deco obligation (or greater than expected deco) make redundancy a very prudent option. The diver should be capable of holding their planned deco...and planned contingency (just longer/just deeper) deco regardless of what incidents occur. Without redundancy, this cannot be guaranteed.

6. What protocols do you use for determining a decompression profile?

Laptop software. For routinely visited sites/depths, I have pre-printed and laminate tables for my 'standard' dives and deeper/longer contingencies.

7. What training is needed to be sure one can handle emergencies at depth? (For example, it is very common in technical diving training to find dives losing buoyancy control when first practicing OOA scenarios, so there is training for that. Even when I was working on my full cave certification, the instructor always did the OOA drills in a place with a low ceiling because of the tendency to ascend.)

- Core diving skills should be exemplary and must not diminish when task loading/stress increases.
- Situational awareness should be excellent and must not diminish when task loading/stress increases.
- Precise gas management.
- Precise dive planning and discipline to follow that plan accurately.
- Appropriate procedures/drills specific to deep diving, such as; assisting diver with narcosis, ox-tox rescue, gas depletion, DSMB deployment.
- Stress management techniques.
- Problem solving techniques.
- Equipment specific training, for instance; doubles shut-down drills, long-hose deployment.

A caveat to all of those is that training itself isn't enough - the diver should be assessed/critiqued to confirm that the standard of their skills is sufficient for the dives to be conducted. It is possible to educate yourself from the internet, or book, and practice with a peer in shallow water - but you still need a mentor or instructor to test your capabilities. It is highly unlikely that a diver can assess their own capabilities effectively - and it is not prudent to expand the demands of your diving without fully understanding your true capabilities.

8. Is any special equipment needed, or is a standard OW rig just fine? (For example, are DSMBs encouraged, and, if so, is deploying them at depth part of the expected training?)

Personally, I feel that doubles are a must for any dive below 40m.. and many dives below 30m. However, in very generic terms...

- BCD should be capable of securely holding the planned number of cylinders.
- Regulator/s of sufficient performance to cope with deep air demands.
- DSMB and appropriately sized reel, because divers may have to ascend immediately in open water (no time to return to shotline or follow bottom contours).
- Back-up computer or depth/timing devices.

9. Do you have a standard limit for PPO2?#

1.4 PPO2 active / 1.6 PPO2 static

 

[BertP]

I haven't read the entire thread yet but I thought I'd comment before I am influenced one way or the other. I am not a technical diver yet but I do plan on going that route. Bear in mind, also, that my original scuba training was in the days when if you knew which end of a tank the reg was to be connect to, you were certified (well, that's a bit of an exaggeration, but not much).

To me, this whole "light deco" discussion is kind of like the discussions surrounding defibrillators years ago. Back then, the only people permitted to use a defibrillator were MD's. If you weren't an MD and used one, you were arrested, shot, tried, convicted and sentenced -- in that order. Today, things are different. Here in Canada, many (most?) hockey rinks have defibrillators readily available for anyone to use. If you know how to read, you can effectively use a defibrillator to save someone's life. Too many people died over the years waiting for an MD to show up and use the defibrillator. That was too much of a waste so it was changed.

Should those of us who are certified as rec divers encroach into light deco? I think that it depends on the person, their knowledge and abilities. Eventually, I suspect that "light deco" will be the norm in rec diving and will be taught as a normal part of OW courses. It may take a while to get there, but responsible discussions like this one pave the way to changing how we do and perceive things. It is simply expanding the envelope just as what has occurred in many other areas of life over the years.

On the other hand, this type of discussion may show that introducing rec divers to light deco is pure folly that results in many deaths. If so, it should be abandoned. Maybe the teiring should be changed. Rec, Deco, Tech, etc instead?

My $0.02

Bert