Suspected Nitrogen Narcosis... And Decompression.

[timz]

I was on a weekend dive trip last Saturday. Upon arrival, we had our first shore dive at 5m depth for 1 1/2 hour. Then we had 3 1/2 hours surface interval before we went for a wreck dive with 28m depth.

So, this was what happened. We descend through a buoy line and reached the wreck at 28. And we separated from the DM within a minute due to poor visibility (3m). 3 of us however, decided to continue diving with all our torches on. Saw some nudibraches and tunicates, and we did some shots(photography). Swimming around the wreck, looking at the Dive Com, the NDL says 5 mins and I suggested an ascent. So, we did.

Remembering the DM briefing about the Dive site was to have a deep stop and a safety stop. But couldn't remember what was the depth and stop duration. we ascent while looking at the dive comp, it now shows 5 mins, small deep stop and ceiling. So, I thought it was a deep stop. So, we waited a while and the 4 mins did not move where the Dive time has jumped a min or more. Feeling a little impatient, I told my buddies that we're ascending slowly anyway. So, we did.

While ascending, I realized the number increased and the first thing that came to my mind was, "Why is the number increasing. Is it because we didn't stop enough and we have to stop longer now..?" Didn't care much and we continue ascending.

When we reached the depth about 20m, Suddenly logic and rationale came back. I looked at the dive com again and now it shows even more time. Then I realized i made a mistake and I signaled to my buddies that we're ascending to 14m for deep stop.

Back home on Sunday. While logging my dives on Monday, filling up the details and pressure group of that particular dive, I realized that if you start a dive with Group A, the maximum bottom time we have for 28m is only 20mins. And the dive profile of that dive indicates we were at 28m for 20mins.

I think it was narcotic effect that have causes my response to slow down and poor ability to analyze. How could I mistaken NDL with Deep stop.

 

[Reku]

It is quite possible you could of been narked even at a shallower depth such as the one you were at. In any case I would suggest getting maybe some wetnotes or a slate and writing down when you will do you stops and how long you will stay at a specific depth, maybe even write down the max NDL time of the depth - that way you can reference it when you reach your target depth or halfway through and all will be well.

That's what I do even on shallow dives or easy dives and it works amazingly well - I don't really have to remember any specifics - just make sure what you write down is accurate and that you write everything you need down and remember to check it once in awhile.

You should try and remember it all but the notes help for when you can't - it's nice to have a plan physically written down.

 

[Diver0001]

I think it was narcotic effect that have causes my response to slow down and poor ability to analyze. How could I mistaken NDL with Deep stop.

Two things caught my eye. First was when you indicated that the DM had determined the dive plan and you were following his/her instructions. To my way of thinking if you're going to make dives at or near the NDL's at these kinds of depths then you should really have the skills to plan the dive yourself. If it were me in that situation I would have listened to what the DM said but plan my own dive anyway. The only thing I really want to hear from the DM is the maximum dive time.

If you think that through, then I believe this is the root of the problems you were having. You didn't plan your own ascent, you were trying to follow instructions that you had forgotten and then started riding the computer and simply got confused. If the confusion was made worse by narcosis or not may be interesting to know but in my mind it was *caused* by not being in control of your own dive.

That said, mistakes are human nature, so just learn from it an move on. If you take the lessons here then you'll only become a better diver because of it. If I told you about all the mistakes I ever made you'd think I was a risk to myself in the shower! LOL

As for mis-reading the computer, I have actually done that. Almost all of my dives (outside of training) are technical in nature so I've become very unaccustomed to having the computer "clear" during the ascent. At the end of the season last year I was doing a dive with a buddy of mine and during the ascent the computer "cleared" at the 9m stop. I don't remember the exact number it said but I looked at it and saw a number like 212 or something and for a few seconds I couldn't understand for the life of me how I had accumulated so much deco time on what was for us a really tame dive.

My buddy said that he saw me do a double take and had to laugh when I signed to him to stop because I needed a minute to think. He knew right away what had happened but it took me a good 30 seconds to logic it out.

Was that narcosis? fatigue? maybe, but it was also a warning to myself not to get complacent about planning.

R..

 

[timz]

Two things caught my eye. First was when you indicated that the DM had determined the dive plan and you were following his/her instructions. To my way of thinking if you're going to make dives at or near the NDL's at these kinds of depths then you should really have the skills to plan the dive yourself. If it were me in that situation I would have listened to what the DM said but plan my own dive anyway. The only thing I really want to hear from the DM is the maximum dive time.

If you think that through, then I believe this is the root of the problems you were having. You didn't plan your own ascent, you were trying to follow instructions that you had forgotten and then started riding the computer and simply got confused. If the confusion was made worse by narcosis or not may be interesting to know but in my mind it was *caused* by not being in control of your own dive.

That said, mistakes are human nature, so just learn from it an move on. If you take the lessons here then you'll only become a better diver because of it. If I told you about all the mistakes I ever made you'd think I was a risk to myself in the shower! LOL

As for mis-reading the computer, I have actually done that. Almost all of my dives (outside of training) are technical in nature so I've become very unaccustomed to having the computer "clear" during the ascent. At the end of the season last year I was doing a dive with a buddy of mine and during the ascent the computer "cleared" at the 9m stop. I don't remember the exact number it said but I looked at it and saw a number like 212 or something and for a few seconds I couldn't understand for the life of me how I had accumulated so much deco time on what was for us a really tame dive.

My buddy said that he saw me do a double take and had to laugh when I signed to him to stop because I needed a minute to think. He knew right away what had happened but it took me a good 30 seconds to logic it out.

Was that narcosis? fatigue? maybe, but it was also a warning to myself not to get complacent about planning.

R..

Thanks for the advise. I will learn how to plan my dive better.

In South East Asia, most of the divers are too pampered by dive centres that all we do is to sign up for dive packages and the Dive Centres will do all the planning.

Till one day, I went for a dive destination with extremely poor visibility where we separated from our DM. While waiting doing the safety stop, I heard alot of boat travelling. That's when the idea of getting a torch light and an SMB first came to me.

 

[Redshift]

It is difficult to know which numbers you are referring to without having seen the computer, but from your description I'd guess that you had gone into deco.

Besides the fact that you didn't plan your dive and were trying to remember what the DM had said while being possibly narked, that confusion could have also been increased by not understanding the concepts behind an ascent strategy for a dive like that and also the information on your computer? Had you seen it before going into deco?
Because according to your description you had a ceiling and saw a time related to it that did not decrease when you ascended a bit, but also at first it did not increase. Although, since you had only gone up a few meters and were still below 20, the deco time eventually went up again.

 

[Storker]

You didn't plan your own ascent, you were trying to follow instructions that you had forgotten and then started riding the computer and simply got confused. If the confusion was made worse by narcosis or not may be interesting to know but in my mind it was *caused* by not being in control of your own dive.

I totally agree. It's a well known fact that you remember things you do much better than things you're told. By actually planning your bottom time and depth profile yourself, that info is much better engraved in your brain than if you just listen to what the guide tells you. When - not if - you get narked, you have a better chance of remembering that info. It doesn't have to be elaborate, and it doesn't have to be complicated. However, checking the NDL versus planned bottom time - as you did after the fact - would have told you that you'd be uncomfortably close to the deco limit.

For these kinds of dives (rec dives in benign conditions), a plan like "descend to 28m and ride the computer with minimum 5 minutes NDL time" may be enough. Provided you check your computer and SPG regularly, that is. Me, I get easily narked - or I'm just more aware of it than others - so if I go below some 25m, I like to also plan for a maximum bottom time. I don't trust myself when my brain gets a little sluggish.

Anyway, it's a lesson learned and you came out of it just fine. Now remember that lesson and you'll be a better, safer diver next time.

 

[boulderjohn]

Swimming around the wreck, looking at the Dive Com, the NDL says 5 mins and I suggested an ascent. So, we did.

Remembering the DM briefing about the Dive site was to have a deep stop and a safety stop. But couldn't remember what was the depth and stop duration. we ascent while looking at the dive comp, it now shows 5 mins, small deep stop and ceiling. So, I thought it was a deep stop. So, we waited a while and the 4 mins did not move where the Dive time has jumped a min or more. Feeling a little impatient, I told my buddies that we're ascending slowly anyway. So, we did.

While ascending, I realized the number increased and the first thing that came to my mind was, "Why is the number increasing. Is it because we didn't stop enough and we have to stop longer now..?" Didn't care much and we continue ascending.

When we reached the depth about 20m, Suddenly logic and rationale came back. I looked at the dive com again and now it shows even more time. Then I realized i made a mistake and I signaled to my buddies that we're ascending to 14m for deep stop.

OK, I am trying to understand exactly what you said here. Please correct anything I say that is a misunderstanding.

1. You said your computer showed that your NDL was 5 minutes, and you started to ascend. That is very normal.

2. The you said that after you had been ascending a while, "it now shows 5 mins, small deep stop and ceiling." That part has me confused, partly because I don't know what kind of computer you are using. If you signaled the ascent when you saw that you had 5 minutes of NDL, ascended briefly and looked again, it is quite likely that you still had 5 minutes of NDL. As you ascend at a normal rate, your NDL will get larger or stop getting lower because you are getting shallower. It is possible that your computer is telling you that you have a ceiling that is perfectly normal at the safety stop depth; I can't tell without a more detailed description or a look at the computer. On the other hand, it is also possible, depending upon the computer, that the is telling you that you have a mandatory deep decompression stop. That is EXTREMELY unlikely--going from 5 minutes of NDL to a mandatory deep decompression stop requires a very long delay in your ascent--many minutes.

3. You then said you hung around for a minute and the dive time went up a minute and the NDL dropped to 4 minutes. That is exactly what should happen if you are holding depth for a minute.

4. The you started ascending and you said the number was ascending and you didn't know why. That is perfectly normal. As you ascend, you are getting more and more shallow, and at shallower depths, you get longer and longer NDLs. When you get into the really shallow depths, it might jump to 99 (which is as high as it goes) or it may show a - - sign. Then you do your safety stop.

In summary, if I understand what you wrote correctly, you just experienced something that should happen every time you dive within NDLs. The only thing that confuses me is what you wrote in the part I summarized in point #2..

 

[Edward3c]

I was on a weekend dive trip last Saturday. Upon arrival, we had our first shore dive at 5m depth for 1 1/2 hour. Then we had 3 1/2 hours surface interval before we went for a wreck dive with 28m depth.

So, this was what happened. We descend through a buoy line and reached the wreck at 28. And we separated from the DM within a minute due to poor visibility (3m). 3 of us however, decided to continue diving with all our torches on. Saw some nudibraches and tunicates, and we did some shots(photography). Swimming around the wreck, looking at the Dive Com, the NDL says 5 mins and I suggested an ascent. So, we did.

Remembering the DM briefing about the Dive site was to have a deep stop and a safety stop. But couldn't remember what was the depth and stop duration. we ascent while looking at the dive comp, it now shows 5 mins, small deep stop and ceiling. So, I thought it was a deep stop. So, we waited a while and the 4 mins did not move where the Dive time has jumped a min or more. Feeling a little impatient, I told my buddies that we're ascending slowly anyway. So, we did.

While ascending, I realized the number increased and the first thing that came to my mind was, "Why is the number increasing. Is it because we didn't stop enough and we have to stop longer now..?" Didn't care much and we continue ascending.

When we reached the depth about 20m, Suddenly logic and rationale came back. I looked at the dive com again and now it shows even more time. Then I realized i made a mistake and I signaled to my buddies that we're ascending to 14m for deep stop.

Back home on Sunday. While logging my dives on Monday, filling up the details and pressure group of that particular dive, I realized that if you start a dive with Group A, the maximum bottom time we have for 28m is only 20mins. And the dive profile of that dive indicates we were at 28m for 20mins.

I think it was narcotic effect that have causes my response to slow down and poor ability to analyze. How could I mistaken NDL with Deep stop.

I’m with John on this one, without knowing what model of computer you were using we can only speculate. However, those that do deep stops are normally a bit more expensive than the norm. Doing deep stops on a computor not designed for them will increase your deco time whilst you do them.

On my last dive my computer went from 0 no-stop time to 3 at 25m then reasonably quickly to 5 then 6, not until I got above 15m did it start to decrease. By the time I was at 6m deco time had reduced to 4 minutes. My buddy was patient and waited with me. I still exited the water with 80bar after 65 minutes.

Not an unusual dive: me on a 300bar 12Lt and pony, my buddy on a rebreather. And I had planned up to 9 minutes of deco before going in.

 

[Jax]

@timz - will you tell us what computer you were diving, please?

And what were the settings - conservative, liberal?

 

[Bob DBF]

Doing deep stops on a computor not designed for them will increase your deco time whilst you do them

I have been considered dense, but shouldn't your deco time increase while doing a deep stop as it would not be shallow enough to off-gas N2. Not a perfectly planned and executed dive which you calculated the deco including the stop, but say you overstayed the deep stop by 5 minutes, that would by my thinking increase the deco time of the dive.

I have never done deep stops, with the exception that I will hesitate at depth if I feel I'm ascending too fast for too long to keep the total rate on track.


Bob