Exceeding maximum dive time?

[Blackwood]

I think dpbishop's point bears repeating:

"assuming you have sufficient air to complete one"

Gas requirements increase dramatically with exposure. As rstofer and others have discussed, the "no stop tables" are generated for a direct (no stop) ascent at a specified ascent rate. As you can imagine, you generally need less gas to satisfy the deco requirements (e.g. 1 minute up from 60 feet on a 60-fpm table) of a no-stop table than a stop-table.

Decompression isn't black and white. You don't switch from "no deco" to "deco". If you overstay your table by a minute or two and don't adjust the ascent, you could be fine. Likewise, if you understay your table you could not be fine.

But while deco isn't black and white, breathing is. Either you can or you can't.

Gas is the paramount factor.

[/soapbox]

 

[Rhone Man]

All the stuff people said above: just don't do it - avoid the situation.

However, if you only lightly cut the corners of the NAUI table's NDLs, the truthful answer is "probably nothing". NDL limits have a certain buffer built in to them. Additionally tables are calculated on the basis that you are static at your maximum depth the entire dive. If you dive with a computer, you will know that this is rarely ever true.

Statistically it is possible that you might suffer a DCS hit even staying within NDL table limits. You are more likely to suffer one if you overstay table NDL limits, but it is no sure thing. You are starting to roll the dice pretty heavily if you omit deco when your computer says you need to (unless it is a Suunto*). But equally there are plenty of stories of people who have blown planned decompression and survived unscathed. I recall a story from the UK a few years back when a guy ascended from 60 feet like a rocket feet first when his drysuit malfunctioned, skipping about 20 minutes of planned deco. No embolism, no DCS and a serious slice of good luck. Never do something as stupid as that, but it goes to show you as Blackwood said: it is definitely not black and white.

If you do ever blow your NDL limits whilst diving, don't get back in the water for a second dive. Sit it out for the rest of the day.

Lastly: never take advice on decompression diving or other dangerous sports from people on the internet. There are a lot of nutcases out there.

* This comment is a joke.

 

[Teamcasa]

Just started my certification course and am wondering about the following:

1. Using Naui dive tables, what happens if you stay longer than the maximum dive time you are supposed to stay without a deco stop? As an example, what if you go down 60-ft and go beyond the maximum dive time of 55 minutes to, say 65 minutes? Is this dangerous or does it mean you just need a longer deco stop?

2. What about on your second dive if you go beyond the adjusted maximum dive time (AMDT)?

i am also interested in this question. perhaps an instructor or tech-diver here can give some quick pointers?

Here's the thing. Decompression diving is not something a person should learn on the internet.

Getting advice is different from learning.

The advice given in many previous posts is good when it tells you to talk to your instructor. However, this is ScubaBoard where advice and answers flow freely.

With that in mind, here is mine.
Exceeding limits, be it tables or violating your computer is dangerous and should be taken very seriously. That said, most modern dive computers allow diviers to exceed table limits in many cases as they take into account factors that tables do not.

Depending on the actual profile of your dive, you may not have had violated your NDL (no decompression limit). Spend some time reviewing the dive planing threads, you will soon discover what was missing in your dive that day.

Ask the questions, weigh the answers, decide for yourself and most of all, dive safe and have fun.

 

[Rick Inman]

However, this is ScubaBoard where advice and answers flow freely.

Well then, here is what I would do.

If I was recreational diving and suddenly found myself in violation of my NDL (IOW, I now had an actual deco obligation), and I didn't have a deco plan, tables, computer, whatever...

I would begin my ascent at 30FPM. I would pause at 80% of my max depth, continue up to 50', stop for 30 secs, move for 30 secs to 40', stop for 30 secs, move for 30 secs to 30', stop for 30 secs, move to 20', and then stay at 20' for as long as I felt I needed to, or until my gas supply ran to minimum. Then I would very slowly ascend.

Assuming a single tank for recreational dives, it would be almost impossible not to come out clean using this profile.

 

[NorthWoodsDiver]

Exceeding the no-stop time on your tables or dive computer puts you into decompression diving where MANDATORY decompression stops are required.

This is considered a form of overhead diving just like diving into a cave, wreck, or under the ice. Even if there is nothing over your head to prevent you from surfacing we pretend there is.

Diving in an overhead environment is considered "technical" diving and it has certain training and equipment requirements far outside the requirements of your openwater class.

Some examples of changes in equipment or proper training would include:

-The use of redundant equipment, like dual tanks with dual first and second stage regulators.
-Training in the use of mixed gas like nitrox to expedite mandatory stop times or lengthen bottom times.
-excellent buoyancy skills, if a stop is at 10ft this means you must be able to stay at 10ft (horizontal is most common) not at 15 feet or 5 feet or back and forth between 5ft and 15ft.
-open water decompression diving requires the need to signal to the surface with use of a SMB. this can also aid in holding decompression stops when in blue water.
-usually decompression diving means long term time spent in the water so an ordinary wetsuit isn't enough even in warm water. Diving a drysuit is the only other option and it brings considerable expense and its advised to have training in its use.
-creating and carrying tables on a dive for those times when a diver ends up staying longer or needs to ascend before his planned time or having tables for use in case a decompression gas is not usable is also common. These are usually custom cut using software like V-planner but some divers use just their own brain and the theory of ratio decompression to fashion emergency decompression stops based on the bottom time of the dive.
-Divers need to be well aware of their SAC rate when getting into decompression diving. There is no excuse for running out of air and bolting for sunshine when you start diving in overhead environments.

those are just examples and not all of them apply to everyone at all times.

So you ask what happens if you exceed these times, well in truth the art of decompression diving is not fully understood so tables and computers are padded with conservatism and you will see many divers padding things further to add increased safety margins.

If you look at the variety of theory and all the different algorithms out there for computing dive information and you will see that no two brands of computer or no 2 agency's tables provide exactly the information to the diver.

Usually people find a system that works for them and stick with it to the best of their ability to avoid a diving injury.

The old Navy dive tables were designed for navy divers who are in top physical condition, if your not in top physical condition then its good practice to pad the tables based on your specific needs.

If you cant to the time dont do the crime, if your not trained and using the proper equipment for decompression diving dont exceed the tables no-top times.

your instructor should teach you what to do if you run into an issue like entanglement that causes you to stay longer than planned. The best practice here is to be extremely comfortable in the use of tables and/or your dive computer.

If you live in an area where help is not readily available for the treatment of diving injuries you may wish to take some training on the use of oxygen (DAN has a course).

hope that answers your question. T

 

[rstofer]

But the question was asked specifically about NAUI tables. Not PADI tables and not computers.

NAUI tables provide for extended times beyond the MDT (Maximum Dive Time) and mandatory decompression stop information is provided. See NAUI Worldwide Dive Tables Look in the 60' row and over to the 55 minute entry which is circled. This is the MDT. Now look further to the right and you will see extended dive times over mandatory stop times. You could stay as long as 80 minutes with a mandatory 7 minute deco stop at 15'.

Or, look at the 100' row. The MDT is 22 minutes but you can stay up to 40 minutes if you make a mandatory 15 minute stop at 15'.

When I used these tables, I would plan my next dive and write the Adjusted MDTs for various depths on my slate. Then, at any point in time, I could look at my depth gauge (maximum depth needle), bottom timer and slate to determine when it was time to surface. I did NOT write down the extended times and mandatory stops but I probably should have. I did, however, carry the tables and the slate on every dive. FWIW, this predates the general acceptance of computers (circa '88).

It's nice to have tables that don't abandon you should you exceed the NDL (MDT). At some point, it may actually be necessary to stay a llittle longer. Entanglement comes to mind.

There is a downside to using NAUI tables when it comes to repetitive dives. The 1989 version is much more conservative than the current PADI tables. There are many dives that are acceptable to PADI that just don't work with the NAUI tables. NAUI got much more conservative with the '89 edition.

I do not recommend, nor do I practice, exceeding the MDT. I never have and at my age, I won't be starting now. Decompression diving belongs to the trained tech divers. I wish them well but I won't be joining them.

Richard

 

[MXGratefulDiver]

First off ... NAUI tables do, in fact, accommodate what to do if you exceed your no-decompression limits. However, the training also stresses that this is an emergency procedure, and not something you should plan to do.

It's especially not something a new diver should be considering as an acceptable risk ... because the chances are very high that if you're exceeding NDL's, you are also exceeding the air reserve you want in your cylinder to deal with any unexpected circumstance. For this reason alone, you want to be careful not to do this. Because remember ... while an extended deco stop is certainly something you'd want to do, you can ONLY do it if you have a sufficient amount of breathing gas available to stay down that long.

Finally, while people stress the extended stop ... I'm gonna tell you that the rate at which you get to your safety stop is at least as important. Staying at any depth long enough to exceed no-decompression limits is going to saturate your tissues with inert gases, and when you start your ascent those gases will need to come out. Your body's designed to do that pretty effectively if you let it happen at an appropriate rate ... which is why there is a maximum recommended ascent rate in the first place. The closer to saturation you get, the more important it becomes to come up slowly.

And coming up slowly also means AFTER the safety stop. At 30 feet per minute, it should take you a full 30 seconds from the time your safety stop is over until you reach the surface. Many divers forget this part ... even though that's the most important place to respect the ascent rate limits.

In summary ... exceeding your no-deco limits gives you extra things to watch out for ... in order of priority these are ...

- Watch your gas supply
- Come up slowly
- Do the recommended deco stop
- And make sure to complete your dive properly by taking the full half-minute to surface after the deco stop is over

There's an article on my web site that may provide you with some more useful information ...

NWGratefulDiver.com

... Bob (Grateful Diver)

PS - you also asked about AMDT. The answer is you treat it the same as you would if you went over your deco limit on the first dive. Think of AMDT like a credit card with a maximum limit. The limit doesn't go up just because you carry a balance from one month (dive) to the next ... you still have to honor that limit in the same way.

 

[Merlin830]

This gets into planning yor dive. Look at the depth you are going to dive and the no Decompresion limit (NDL) time. Always have a Plan B. Look at the next longer time or two or three on the daive table in case you stay longer then planned and write down the stops just in case.

I am a firm beleiver in Plan B. and sometimes c and D and ......

 

[FritzCat66]

Most computers nowadays will handle accidental slips into deco quite well and will advise you exactly what depth to go and for how long in the event that it happens. So, once you've jumped through the hoop of using tables for your cert class, get a good computer, toss the tables (along with your slide rule and abacus), and never look back.

Even more importantly, learn it well and check it frequently so you don't exceed limits to begin with.

>*< Fritz

 

[mkutyna]

Correct me if I'm wrong Bob but doesn't NAUI recommend that if a recreational diver running tables slips into a deco dive that they should not do any additional dives for 24 hours? I seem to remember being taught that way and that is how I have been teaching students.