Depth: 95 ft, In Deco, 500 psi, No Buddy

[noj3333]

No you are incorrect. If you reread the original description, you will see that i did go into deco, but had only one minute of required decompression.

I understand now.

The divemaster's rule of no second dive if you go into decompression, is based more on the idea that if you are too irresponsible to watch your dive time, then we aren't going to let you do a second dive.

My prior understanding was that deco meant it was not safe for a second dive. Now I understand their rule to mean, "You're not allowed to dive on our boat due to your actions".
I do understand that there is a blurry line between little NDL time remaining and minor deco time, it'not black and white.

Again, ty for the post... I won't be replicating your dive, but I did learn something from it.

 

[scagrotto]

Focusing on a task to the exclusion of situational awareness is not good diving procedure. Experienced divers like DD can get away with this

The way I read it DD didn't lose situational awareness. He chose to exceed his NDL in order to attempt his task, knowing that it would be a very minor deco requirement that would either clear during a normal ascent or with a very brief stop. Even if it was the result of losing situational awareness I wouldn't say that experienced divers "can get away with it". Plenty of experienced divers lose situational awareness and don't get away with it when the "it" isn't something this minor.

Even relatively experienced (50-300 dives) divers were so concerned about avoiding deco

I don't know what's required in current OW classes and it's been long enough since I took mine that I don't remember the fine points, but I'm sure I didn't get a lot of info on deco theory. I'm pretty certain that I had the idea of not going into deco drilled in fairly thoroughly. I found learning tables to be a good way to get at least a basic grasp of how tissue loading actually happens, but since I took my course an awful lot of divers have gotten certified without learning tables, since computers have become cheap and are very good at doing the math correctly. That leaves me completely unsurprised by the idea that many divers think that deco involves some kind of black magic, and absolutely any violation of NDL by the untrained is a very bad thing.

am I correct in saying DD did NOT go into deco, due to his actions once he ran out of NDL time??

The exact physics of deco theory may be a bit fuzzy, but the calculations made by your computer will be very precise. If your computer counts your NDL down to zero then you are in deco as of that instant. That said, it looks to me like he was at 83' when he had 2 minutes left, and then descended to 101'. That would make things a bit more complicated than simply counting the remaining time down to zero.

'deco on your first dive = no second dive'

Residual nitrogen is residual nitrogen. It doesn't matter whether it's the result of a dive that always stays a bit shy of NDL, or a deco dive with the necessary deco stop. If your residual nitrogen was low enough to surface then you can go back for another dive. How much residual nitrogen you have determines how deep and long that next dive can be. Whether you went into deco deliberately or because you're too stupid to pay attention, and your ability to calculate residual nitrogen and NDL for the next dive are separate issues.

 

[lowviz]

...//... The exact physics of deco theory may be a bit fuzzy, but the calculations made by your computer will be very precise. ...//...

Well,yeah but it is trying to track YOU. And you are neither precise nor reproducible.

Your computer is a bit of electronics kit that some programmer set to be the best compromise for the masses. Don't fall into the trap of worshiping its output.

 

[Kevrumbo]

Those who are more likely to screw up underwater are less likely to spend time and effort in planning.

In other words, people who sift through these posts and take initiative to learn more about gas planning probably aren't the ones who were going to find themselves in deco with low air anyway.

So then this begs the question: did DD actually plan to have enough gas in the redundant pony bottle to cover his deco obligation with critical low gas pressure in his main cylinder source? Typically with a pony bottle back-up, you don't complicate matters by deliberately going into mandatory deco should you catastrophically lose your primary cylinder source. . .

What to do in this type of situation?

On a recent lobster dive I happened to capture my computer readings and gas pressure readings for the end of my dive. I pushed the no-deco limits to catch a lobster, wound the “clock” down to ZERO minutes leaving me ZERO No Deco Time. Then, as soon as I started my ascent, the computer kicked me into a REQUIRED Decompression Dive.

My gas pressure at this time is about 500 psi (in a 108 cu-ft, steel tank).

Certainly it is NOT recommended or safe for recreational divers to push the limits or go into deco and they probably should be saving more air for the ascent as well. Many people are taught the simplistic rule of: be on the boat with 500 psi – which may be inadequate.

The reason I made a video of the ascent is to demonstrate that this is NOT the time to panic or get really worried, or rush your ascent, or kick up hard or begin to breathe fast or get overly stressed out.

We have many examples of divers who have never seen their computer in deco and once it happens they kinda freak out and rush to the surface – breathing like a freight train. Sometimes I think they feel their goal is to get on the boat with as close to 500 psi as possible – so the faster they rush to the surface the less “trouble they are going to be in”. This is NOT the way to handle such a situation. (Most instructors would say that the best way to handle this situation is to avoid it, but that is not the point).

This video demonstrates what I do (or did on this occasion) in this situation. Keep in mind that the deco penalty is as small as it can be (only one minute), but many people would be very concerned by “being in true DECO” and also having just 500 psi at around 100 ft depth.

Instead of exerting myself, you can hear me pop the inflator and get just slightly buoyant so I can drift slowly upward with zero kicking. I slow my breathing and RELAX. I go up SLOW, I check my depth frequently and carefully monitor my ascent rate.

This video is in real time (except for the pauses during the console reading). By the time I reach a depth of about 44 ft (I think it is) – Wow.. my deco penalty is gone - and I have many minutes of no deco time back on my computer.

This is not surprising to a good percentage of experienced divers.. come up a little slower than the maximum ascent rate, relax and your deco time will “clear itself” before you even get close to the decompression ceiling depth. For them, the video will be trivial and boring (maybe that is the point of the video).

My objective in posting this is NOT to advocate or recommend that any recreational diver put themselves in deco and they certainly should preserve a safe volume of gas for their ascent (and enough to share with a buddy). My goal is to provide a simple example that if you (unintentionally) go a little into deco, it is possible to make an ascent using a modest amount of gas, do it reasonably safely and this is NOT THE TIME TO RUSH TO THE SURFACE.

For this dive, I was alone – so I had no need to reserve air for a buddy, I had an independent bail out bottle (a pony bottle) as a back up and I was not diving in an aggressive or reckless manner. I continued a slow ascent and completed an additional safety stop on this dive (as I do on almost every dive) and exited the water with a few hundred psi remaining (and a full pony bottle).

Making an ascent from this depth while sharing air with a panicked buddy and having to exert yourself would result in air consumption rates that would be 5 or 10 times higher than shown in this video, so please don’t interpret this as a suggestion that people should be starting their ascents from 100 ft with 500 psi! The objective is to show what it might look like if you over-stay “your welcome” for a few moments and how it might be handled – even if you have not reserved a whole lot of air.

Since the intended audience is inexperienced recreational divers, it is also very important to remind them that if they continue to remain at depth (once the computer kicks into deco), the penalties (i.e., true deco time) will accrue quickly and a 1 minute deco stop can turn into a 5 or 10 minute stop faster than you can catch a lobster… Especially if you are silly enough to do this on the 3rd dive of the day. This can be a serious or life threatening situation if you don’t have the gas and skills to deal with decompression.

Maybe others will find the topic useful?

Per this ascent strategy in the video below, you'll need 40cf for two divers to reach the surface from 100' (see 15:00 mark in video):
For one diver, this is half of 40cf which equals 20cf --in a steel 108 that's conservatively 570psi from 100'. With no ascent strategy other than 30'/min ascent rate, it would take 9cf and 240psi to surface from 100'. The RMV Surface Consumption Rate used in these calculations is a stressed 1cf/min (which DD appears to have under control by retaining a near nominal non-stressed breathing rate during the ascent, surfacing with "a few hundred psi and a full pony bottle").

Question: what was the actual volume of your redundant "full" pony bottle back-up, motivating you to encroachment of your primary cylinder's Rock Bottom gas supply along with going beyond NDL?

(IOW -crassly & curtly asking the same question:
-->How much was in your Pony to pull-off & video such a stunt???)

 

[lermontov]

So then this begs the question: did DD actually plan to have enough gas in the redundant pony bottle to cover his deco obligation with critical low gas pressure in his main cylinder source? Typically with a pony bottle back-up, you don't complicate matters by deliberately going into mandatory deco should you catastrophically lose your primary cylinder source. . .

(IOW -crassly & curtly asking the same question:
-->How much was in your Pony to pull-off & video such a stunt???)

well unless DD tells us we dont know.
But I suspect DD did the dive decided to push the margins then retrospectively showed the video to demonstrate how to deal with it if you ever got into that situation.

I happened to capture my computer readings and gas pressure readings for the end of my dive

Id prefer it if it read 'I decided to stay down longer and video how to deal with unexpected deco using my pony as back up in the demonstration' At least that way the video is purposed towards instruction rather than an excuse after the fact
I could be wrong but I cant imagine any instructional organisation endorsing this

 

[clownfishsydney]

I have no problem at all with the fact you went into deco, but I do that you only had 500 psi and were at 100 feet when this happened (this is what I have assumed from the information). If you were diving off my (private) boat, then you would not be invited back if this was your normal way of diving.

On a dive to a similar depth that we do in Sydney, I would leave the bottom with a minimum of 110 bar (1500 psi). However, I accept that I use less air than most people, so I would accept 1000 psi as a minimum.

 

[admikar]

I understand "slow ascent to clear deco" action taken by DD. Since this is intended for new/ish divers,if you're low on air, shouldn't it be better to go up faster, up to your deco ceiling to conserve air? One minute at deco ceiling is less air,than one minute longer slow ascent due to deeper average depth. I am aware of dangers of bubble forming in doing so, so I am not asking about rocket zooming to whatever ceiling is, just to see if my thinking is right?

 

[rongoodman]

I understand "slow ascent to clear deco" action taken by DD. Since this is intended for new/ish divers,if you're low on air, shouldn't it be better to go up faster, up to your deco ceiling to conserve air? One minute at deco ceiling is less air,than one minute longer slow ascent due to deeper average depth. I am aware of dangers of bubble forming in doing so, so I am not asking about rocket zooming to whatever ceiling is, just to see if my thinking is right?

You can usually fix bent. Drowned, not so much.

 

[dumpsterDiver]

I understand "slow ascent to clear deco" action taken by DD. Since this is intended for new/ish divers,if you're low on air, shouldn't it be better to go up faster, up to your deco ceiling to conserve air? One minute at deco ceiling is less air,than one minute longer slow ascent due to deeper average depth. I am aware of dangers of bubble forming in doing so, so I am not asking about rocket zooming to whatever ceiling is, just to see if my thinking is right?

Your thinking would be correct if the air supply was critically low. Even if I was at zero psi in the main tank,I personally had a 13 cu-ft pony (if I recall correctly) to make the ascent - so there was no need to rush to the surface, I had the luxury of coming up slowly and clearing the very small deco penalty by the time I reached 44 ft or so.

It took me only about 100 psi to ascent from about 100 and get to 44 ft (where the deco cleared) and since I was calm, relaxed and was not exerting myself, my air demand would remain low giving me more than enough air to continue to ascend in a controlled manner and do a safety stop - without running out or using the pony.

So in this situation, your safety would not be enhanced by rushing to the 10 ft deco stop ASAP- Obviously a diver has to make some decisions if they are at 100 ft with less air than they would like and no pony bottle.

The video shows that this particular ascent was trivial and simple and required very little air. That demonstration may give others the confidence to not rush to the surface unnecessarily (if they screw up).

Of course it is more important to have something to breathe than to worry about the consequences of violating a decompression ceiling, but a diver has to make reasonable decisions, once they put themselves in that type of undesirable situation.

Again, I am not advocating for recreational divers to push the NDL or to start their ascents with too little air.

Also. one of the things I dislike about the discussions on this forum has to deal with people bragging about how little air they use. My personal SAC is not low at all. I am over 200 lbs and not young and use a good bit of air. I have found out long ago that trying to use less gas than is needed will give me headaches and it is actually quite dangerous for a variety of reasons.

So one of the things that divers should be able to discern from the video is that if you start the ascent calm and rested and not sucking wind, and you don't kick up, but "drift" upward using the BC and breath control, you can remain motionless and this may keep your air use to a low level - at least for the few minutes it takes to get a lot closer to the surface.

So even if you had no pony bottle, had 250 psi in your 80 ft tank, no buddy and a short deco, putting a puff of air in the BC and trying very hard to relax and watch the computer would probably be safer than swimming really hard and trying to get to 20 feet in 60 seconds or something. It is really important that you not use the large quad muscles and keep your arms calm if you have to make a low on air ascent (and want to preserve the air supply). This sort of situation would be a true EMERGENCY, but that means it is more important that your response to it needs to be appropriate.

For me personally, I would be pretty comfortable swimming to the surface from 40 ft depth with no air in an emergency. Much deeper than that, my comfort level drops a lot - so anything 60 feet or deeper will cause me to carry a pony bottle - even when diving with a buddy.

In general, I do some diving in 20 feet and carry no pony bottle and everything else is 50 - 60 feet (or more) - so I always have a pony.

 

[oldschoolto]

And let's not forget that this is a computer saying your in deco... There is wiggle room for a reason built into them...

And, Having 500psi is far from running out of gas.. Because PADI and all the others have brainwashed the masses, Does not mean that what most of us old time divers did or does is dangerous..

I don't see a thing wrong with that dive.

Jim