As a rec diver, what to do if I breach my computer's NDL???

[tomfcrist]

I would ensure it is clear that light exercise during deco is beneficial, but exercise once surfacing is unwise.

That being said heavy cardio exercise 20-24hrs prior to the dive is extremely beneficial, resulting in less bubble formation and smaller bubbles when they are formed.

 

[Hatul]

If you accidentally get into deco, you just ascend and make a controlled multilevel dive. Almost all the time the light deco will clear on the ascent. That assumes you have enough gas, if you don't then that's another story.

 

[ianr33]

. Almost all the time the light deco will clear on the ascent. That assumes you have enough gas, if you don't then that's another story.

Agreed! And while I wouldn't recommend it,missing a few minutes deco is probably not going to cause any harm. Roll the dice enough time though and it will catch up with you.

 

[boulderjohn]

As far as that being taught in the tables class, I wasn't taught it when I took my OW (2004) and I was taught the tables. What's funny, though, is I remember the tables being an optional class....with no option if you didn't take it. I don't remember computers being mentioned at all. Then again, it was nearly half my lifetime ago....so it was probably different than how I remember it now!

Tables were required in 2004. The computer version of the class is only a couple of years old. The emergency deco question was on the final exam in 2004, as it is now. Computers are barely mentioned in the table version of the course, but they are mentioned. Again, there is even a question about computers on the table version of the final exam. I would guess that you just don't remember a small detail like that from a decade ago. Heck, I can barely remember what happened last week.

 

[dumpsterDiver]

This is an attempt at splitting an OT conversation from another thread, I apologize if I do a bad job . The discussion started wandering and ended up at this topic. If you're a rec diver, with OW or AOW or even Rescue training, but no deco training, what do you do when your computer starts yelling at you? How does deco work? What can you salvage?

In simple terms, incurring a deco obligation means that your computer thinks that you'll probably get bent if you go straight to the surface. Many computers, especially "rec" computers, will add a safety stop time to your deco obligation. What this does is it gives you a "Virtual ceiling," which is a term many have heard before. This means you had might as well have rock above you, because you CAN'T go above that depth (statistically, according to your computer's model) without getting bent. Remember, always better bent than dead....but with a little care you can easily reduce your chances of getting bent, as well.

First off, let me say you shouldn't be meaning to go into deco. This should be something that either happens because you weren't paying attention or because you had extenuating circumstances. Do not go into deco without appropriate training, equipment, and planning.

No computer is truly a "rec-only" computer...they'll all track you into deco. Also, all of your dives are technically "deco" dives as you're decompressing on ALL of them. So, if your computer goes into deco it doesn't mean it's given up on you. It'll track your loading until it's all gone, which is usually 18-24 hours, depending on algorithm. An algorithm is simply the method by which it "tracks" your nitrogen loading. Algorithms are exact, but they don't exactly predict real life. They're our best guess on how to keep the bends statistically out of our lives. If you DO go into deco, most computers will give you a ceiling. Do not exceed that ceiling. Go shallower as soon as you can, but ascend slowly. Hang out as shallow as you can. Your most aggressive off-gassing occurs at the ceiling, but that is dangerous as you're pushing your limits AND you might get dragged to the surface easier. Try to hang out at a safe depth slightly below the ceiling. Most computers will give you a ceiling at 10ft before anything else happens. In that case, I like to hang at 20ft or maybe 15ft if the water is calm. Watch the timer drop until it says you're safe to surface. At that point, you can go on up. A question was asked in the other thread about extending your dive, so ascending but not to a deco stop. While this is possible, you've already pushed your luck by going into deco. Wait out your deco, wait for your computer to clear, extend your safety stop, and then get back on the boat. An important thing to note is that ascending the last 10-20ft from your safety stop is the most crucial to take slowly. Ascend so that it takes a couple minutes to surface. Then, rest. Relax. Excercise is likely to get you bent. You might even want to sit at the surface a while (5-10min) if it's an option. See if somebody can get your gear on the boat for you. If you see/feel any symptoms, inquire about O2 on the surface, NOT under water. If I were you, I'd call it for the rest of the day.

I'd like to hear from experienced divers, what you think of my synopsis. Should I have changed something? From rec-only divers, what do you think? Do you have any questions?

I think there's a lot of merit to this, but I'd like to stress that this is ONLY if you mess up and accidentally incur deco....nobody should be doing this without proper training.

I've used various computers to do many hundreds if not thousands of deco or close to deco dives. it is important to know what to do when you go into deco, but some of your comments are over the top. I've only been really bent (for sure) once when following a computer.

You are absolutely WRONG if you think that exercise after a light deco dive will likely get you bent. I've often done work after deco, swimming to the boat, hauling in an anchor line, shoveling ice, moving tanks, even snorkeling after a dive. Furthermore if some clown gets to the surface and says: "hey I went into a few minutes deco, so can you lift all my heavy gear out of the water for me" .. well that would.... I don't know what we would do.. it is so stupid I'm not sure how I would respond..i'm not sure why somebody would think I should be lifting their heavy gear after my deco dive anyway..It is NOT good practice to do heavy work, but the chance of getting bent from it, is still very small. Climb you own fat butt up the ladder.

Also, the idea that you must ascend from 10 feet at this super slow rate is not practical in many situations. If coming up an anchor line in rough seas and a big boat you will get absolutely thrashed trying to hang on at a depth of 7 feet and if you let go, the current will likely sweep you under the boat and the bow will crush your skull.. So that might not work so well. Also drift diving with a live boat.. you are very vulnerable at very shallow depths, you want to get to the surface, look around and be visibile, not hang at 5 feet. Plus in both situations, trying to hang at 4 or 7 feet in 6 ft waves is just not going to be practical, safe or necessary. Come up slow from 10 ft, but it does not take minutes.

You also made a comment about if you go into deco a little and accidentally, it won't be that long, so don't freak out. That too is not entirely accurate. if you have done one dive and go a little into deco, your hang should be short. But for many computers I have used, if you do several aggressive dives in a row and then go kinda deep, say 120 or deeper and go into deco. the computer will be pissed and you will immediately (or nearly so) be spanked with a considerable deco stop of maybe 8-10 minutes and it will not clear effectively or in a timely manner if you come up super slow and hang at 40-50 ft etc... So the more accurate advice would be, if you have done a bunch of repetitive dives, you gotta really watch that computer, because it will spank you.

People should also be cautioned that if they have just a few minutes of no-deco time left at say 80 feet and they shoot down to 110 for just a quick look, the computer may also seek revenge (I know this should be obvious), but maybe not?

 

[scubadada]

Great theoretical, conservative SB conversation. Let's be practical. I purposefully do light deco on about 5% of my dives. For the last 300+ dives these have had a range of deco times between 2 and 9 minutes with an average of just over 4 minutes. I know exactly what my SRMV is and do careful gas planning. I always have more than enough back gas and have a redundant supply, which I have never used. I'm absolutely sure that I am not alone in my practice, if nobody else, I'm with dumpsterDiver.

 

[DevonDiver]

There's been some articles suggesting the frequency of diving has an impact on DCS susceptibility (I need to find those references). In short, very frequent diving improves the ability to off-gas efficiently. There is also the 'sample size' issue of dives conducted - whereby very frequent divers have probably ruled out physiological factors (such as PFO) over the course of their diving development. Novice divers don't have that off-gassing efficiency, they don't have that assurance in their physiology and they don't have the 'fine control' on ascent that more experienced divers take for granted.

The point of saying that is to highlight that colloquial stories from experienced divers about when you will, or won't, be likely to get bent are not applicable in general. If you've done a thousand dives under given parameters then it's fair to assume that you won't get bent doing more of the same. If you've done a couple of dozen or hundred dives, in varied/different parameters, then you shouldn't make any assumptions whatsoever based on what does, or does not, happen to you (or others who might seek to 'advise' you).

There's enough multi-million dollar hyperbaric chambers around the globe sustaining themselves financially from recreational divers getting bent.

 

[doctormike]

Why would I surface with an uncleared computer and several hundred psi???

Wait at 15 -20 feet until the computer clears or you are at about 100 psi - or whatever is low enough in your particular tank to do a comfortable very slow ascent from 20 feet. Personally that would be until the reg starts to get hard to breathe. (Depends on surface conditions of course)

300 psi in an AL80 is rougly 8cf which is enough at 20 feet to stay another 8 - 16 minutes depending on sac. That is what the reserve is for, it does you no good at the surface.

I don't think that this is a good contingency plan, especially since you are recommending it for an OW diver without deco training, who is already presumably stressed by the situation. Sucking the tank dry or riding it down to what you think is a minimal reserve, then ascending the last 20 feet involves several problems:

1) New diver with weights on the surface with an empty tank, possibly not near a boat. All it takes is forgetting to blow some air into your BC and they might be back underwater, but now with no gas... panic spiral, etc...

2) Biggest pressure change is near the surface, right? So if you suck the tank dry at 20 feet, most new divers are going to make a pretty quick ascent (I know that you said to go slow, which is good), but that might add to their DCS risk more than enough to offset the off gassing that they did with those last few PSI.

3) Gauges are notoriously inaccurate at the low end of the range, so if you want to keep a little reserve, 300 PSI might actually be 100 PSI, and 100 PSI might be fumes.

 

[Mr Carcharodon]

As a rec diver, what to do if I breach my computer's NDL???


Well try doing 1 minute of deco for each minute you go over NDL. This begs the question at what depth to do the deco and the usual answer is to do it from half max depth up to the surface. You will want to shape the ascent curve with exponentially more time at shallow depths than at deep depths. "Exponentially" sounds tricky but really you just break ascent into 10 foot increments and fix the middle depth and take time from the deep half and add time to the shallow half. And of course you should be doing 1 minute stops at 30, 20 and 10 feet anyway so this is on top of that. Now if you cannot hold your stops or be sure you have enough gas you have no business doing this in anything other than an emergency but it is good to have a contingency for an emergency. Do (yes really you must do this) try calculating your stops in a decompression software like v-planner and see how close you come to their plan. Do it enough that you come pretty close, you will.

If you are not comfortable with this, and you might not be if you were cold, stressed, tired or did a lot of work on the dive then add another minute or two or three at the last three stops. Also take your time from 10 fsw to the surface.

 

[NAM001]

Sounds like the dead horse of what is the safey stop for. If you are down and the puter yells deco you head up and your 3 min safety stop should take care of it for you. I wish I knew more about when and the conditions the 3 min rule came to because it sounds like the type of rule that would be used when using tables and watch with no computer. You know the table says things shold be ok but just in case you are not the model diver and making the model dive here is 3 min to CYA at 6m. The same CYA I would think would cover the broach of ndl if one promptly ascends when the puter yells at you. Any way if you go up to safety stop like others have said adn jsut wait for the computer to return to normal before surfacing you should be ok. Of course hanging up your fins adn mask for the day is a good idea also till furher trained