Varying NDL ascent strategies

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boulderjohn

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I am currently doing research for a potential article on the various ascent strategies officially advocated by different groups and agencies for dives that do not require decompression stops. The overwhelming majority of divers and the agencies that trained them advocate an ascent, usually 30 FPM, with a 3-5 minute (usually) optional safety stop between 10-20 feet. Some groups officially advocate other strategies. I am looking for information about those other strategies--what those strategies are and especially why they are advocated.

I have already contacted both NAUI and GUE headquarters, and both have given me clear and complete official explanations. I do not need anything more from them. I have also contacted UTD headquarters and am awaiting a response from them.

What I need, then, is information about any other sources I might have missed. I don't want to leave anyone out.

I want to stress that I am looking for official information from established organizations. I am not looking for anyone's individual belief about what they think is official, because however well intentioned, those sources could be wrong. I am also not looking for what any individual has decided to do for personal reasons.

I do not want to start a debate about any of this here--I am just looking for some basic information. If you want to discuss personal beliefs, feel free, but that is not what I am interested in.
 
BSAC 88 Tables

Ascent rate 15m/min to ascent check depth.
In the case of a no-stop dive, thats 6m.
Stop. Check you are inside the No-Stop time, if so, Then 1min to the surface (6m/min)
(If NOT inside NDL, then follow stop requirements as specified by the tables).

If using a dive computer, follow the dive computer.


NOTE - The BSAC88 tables show information for both a no-stop dive, and a dive requiring compulsory decompression stops.
They are also multi level (altitude tables).

BSAC88 table format
 
BSAC 88 Tables

Ascent rate 15m/min to ascent check depth.
In the case of a no-stop dive, thats 6m.
Stop. Check you are inside the No-Stop time, if so, Then 1min to the surface (6m/min)
(If Not inside NDL, then follow stop requirements as specified by the tables).

If using a dive computer, follow the dive computer.
So no safety stop for any extended time?
 
Its quite an old table now, developed by Dr Hennessy and released in 1988. So, really, before a'safety stop', was considered good practice.
Once you are at 6m, you can stop as long as you like, you are viewed as decompressing. However, the dive is still ongoing until you surface. Your Surface interval doesn't start until you surface, and your surfacing code would potentially need to be adjusted to take into account the extend delay at 6m.

Tables are still taught, but real world, everyone uses dive computers. There is even a set of (Level 1) Nitrox tables, for mixes 21%, 27%, 32% and 36% mixes.

I've added a dive conduct slate here, technically, you are supposed to fill this in when you plan the dive, and carry it with you during the dive. This is what you refer to at the ascent check depth.
As I said, everyone now uses computers, so its a little academic.
 
The Norwegian Standard Tables are used both for sports diving and professional diving, so they cover both no-stop dives and dives with staged backgas deco up to 60m depth and 20m bottom time (that depth and bottom time is not recommended). Standard ascent rate is 10 m/min. Our tables don't include dedicated nitrox tables, but a nitrox certified diver is supposed to be able to calculate their EAD and use the air tables.

1* divers are taught that they should do a 3 minute safety stop at 3-5m. That's normal practice also at higher levels.

In practice, students are told "follow your computer, but do the safety stop", but knowledge of the tables is still required in the syllabus.
 
The material I have seen from the FFESSM (Féderation Française d'Études et de Sport Sous-marins, "French Federation of Underwater Studies and Sport", in a free translation), for recreational divers, follows a table developed by the French navy, MN90. This table uses an ascent rate of 15m/min up to the first stop (it includes deco diving procedures). The table does not explicitly mandates a safety stop.
 
Ascent rate 15m/min to ascent check depth.

This table uses an ascent rate of 15m/min up to the first stop
And me thinking, when we did our 3* and were tasked to follow standard ascent rate up to the 6m stop, that 10 m/min is pretty damned fast. It wasn't that easy to keep that ascent rate while following the bottom, and doing it in free water while being able to actually stop at 6m isn't something I'm quite certain I'd be able to do.
 
And me thinking, when we did our 3* and were tasked to follow standard ascent rate up to the 6m stop, that 10 m/min is pretty damned fast. It wasn't that easy to keep that ascent rate while following the bottom, and doing it in free water while being able to actually stop at 6m isn't something I'm quite certain I'd be able to do.

I don't think anyone would ascend at that rate, these days. I should have phrased it as the 'maximum' ascent rate is 15m/min. The 'maximum' descent rate is 30m/min.
One of the unique things about the 88 tables, at least at the time, was the slowed ascent rate from 6m to the surface.
 
I don't think anyone would ascend at that rate, these days. I should have phrased it as the 'maximum' ascent rate is 15m/min.
We were told that the tables were based on 10m/min until the first stop (perhaps it was 9m or 12m, I don't quite remember since I wont be doing deco dives and subscribe to Sherlock Holmes' theory about remembering useless stuff), otherwise we ran the risk of on-gassing too much for the table to be completely valid.

Given that nearly everyone is using a computer these days (at least for the kind of light backgas deco included in the 3* syllabus), and the computer tracks any ongassing during a "too slow" ascent, I assume that it was an exercise in following a predetermined ascent strategy rather than a real deco exercise.
 
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