First dive at 40 meters - Newbies recreational

[David Novo]

@Dody, rereading your description there are a lot of red flags (such as deco dive to 40m with a 12L of air - the second cylinder was not with you).

I would work on the basics before considering a tech course in the near future.

 

[Dody]

I'm assuming the DM was being supervised by your Deep Diver instructor and the instructor was somewhere nearby? I'm PADI, so I don't know the SSI course.

Please don't take judgement at all on the following as I'm always interested in various courses around the world. But I'd personally be concerned with aspects of the dive. I'm glad you're writing about it and hope you had a debrief with your wife and DM about how it could have gone better and what you learned. For example:
- going past decompression limits on a training dive.
- was there discussion on emergency deco procedures, or was the computer to be followed? PADI has specific guidelines on dealing with emergency deco, I assume SSI as well. What would you do on computer failure?
- you say you spent time at 20m, approximately 10 minutes. This would eat into your overall NDL at 40m, which would already be about 10 minutes with a normal straight descent, and of course, your air reserves.
- could the DM have kept to the plan and NDLs better?
- sounds like your descent was too slow and your ascent not fast enough. Can you confirm that with your dive log? A dive to these depths needs execution and skills not far off from tech diving, so you got a taste of what's needed and what can happen if you're off.
- separation of team members - the DM seems to have been at different depths and maybe not available to help during the strong current
- that some of the feelings you described during the ascent were likely narcosis induced
- some form of depth buffer, like planning for 37m (120') instead of 40m/130' (more a comment on how an instructor might build in some conservatism based upon the site or conditions)

The good points were that you finished the dive, dealt with a bit of a scare that worked out, stayed calm and in control, followed the computer guidance instead of bolting to the surface, and added conservatism to the safety stop. Congratulations and thanks for sharing!

Hello, I will try to respond point by point.
Before the dive, I had ran a complete simulation on my PC. My main concern was not exceeding the NDL but being short on gas as there was recently a thread on SB about whether it was safe to dive at 30 meters with a single cylinder.
- NDL at 40 meters is 5 minutes. The simulation had given me 3 minutes max at 40 meters. That's why I was surprised when my computer indicated 1 minute after maybe 30 seconds. As the plan was to ascend straight to 25 m, deco was out of the equation so there was no deco emergency procedure. The decision to start at 20 meters was only to make sure that we were comfortable before going deeper and all the parameters were green.
One thing that we should have had maybe was a pony, but when I raised it to the instructor, he said that the emergency cylinder at 5 meters was enough.
- I mentioned that the descent was too slow because for me, it is the only explanation for 1min NDL warning so soon. In the simulation, we were at between 20 and 40 for 10 minutes and the descent to 20 meters should take 2 minutes.
However, the ascent was not too slow. It was just a matter of perspective and perception on my part. From the computer, we ascended from 40 to 25 at 7 meters/ min.
- The DM was above us and he was alert. When I said afterwards that I was pleased that neither my wife nor I did panic, he said that he did not see any sign of panic and that we had acted both as we were trained and briefed. I think that we need to factor in the stress that I was probably feeling for my first dive at 40 m. Even though, I always say that I am immune to stress, well, sometimes, I overthink too much and make calculations and assumptions in the heat of the moment that might complicate things.
- I agree on a safety margin at 40 m. I am a big advocate of safety margins. And we had none in terms of NDL and a too small one on air if something really bad had happened. Buddy breathing would have been ok but a down current to say 50 meters would have left us in a bad predicament with only the computer to tell us what to do to deco. I am confident that we could have managed getting out of it ( I have never experienced a down current but this is one of my fears so I fully programmed my mind to react to that. Hence, the 45 degrees as we could not use the reef as a shelter).
So, there are goods and bads in this experience as in any dive especially when you do something new but more goods than bads.
Bads are: not enough safety margins in NDL and air. I should have ran more simulation scenarios.
Goods are: all the rest. We followed the dive plan and all went well.
I might have been affected by narcosis after all but I was still able to rapidly calculate how much breathing time we still had.

 

[Blackcrusader]

Hello, I will try to respond point by point. Before the dive, I had ran a complete simulation on my PC. My main concern was not exceeding the NDL but being short on gas as there was recently a thread on SB about whether it was safe to dive at 30 meters with a single cylinder.

Your real error was assuming your sac rate was 11l/min to calculate the rest of the dive. This is your best case not your average rate. The fact that you had such a short dive time of 40 mins and used 140 bar shows your air consumption was quite high. Much higher than you assumed before the dive. Main thing is you completed the dive and can reflect back on it.

By the way it reflects very badly on an instructor letting you go to 40m and have deco obligations on a non deco first training dive to 40m. Your wife is also a student doing the same course and dives? The instructor should have been at the same depth as you and certainly not have let you get to 1 min to NDL at 40m not have been above you watching.

 

[David Novo]

One thing that we should have had maybe was a pony, but when I raised it to the instructor, he said that the emergency cylinder at 5 meters was enough.

This relates to a point someone raised on a different thread of yours: you are doing trust me dives.

Buddy breathing would have been ok

You also did not have another second stage?

Bads are: not enough safety margins in NDL and air. I should have ran more simulation scenarios.
Goods are: all the rest. We followed the dive plan and all went well.

I do not want to burst your bubble but there are at least a couple more of aspects you should consider:
1) You were ocean diving and when the current drifted you away, you should have used a DSMB, to alert your and other boats;
2) Horizontal vs vertical ascents: just some food for thought;
3) Buoyancy control: if you have to kneel on the bottom, you need to work on it.

Your real error was assuming your sac rate was 11l/min to calculate the rest of the dive. This is your best case not your average rate.
The fact that you had such a short dive time of 40 mins and used 140 bar shows your air consumption was quite high. Much higher than you assumed before the dive. Main thing is you completed the dive and can reflect back on it. You also said the DM used the same air as yourself and your wife is that correct? For this dive or just other dives?

And this: if you had a catastrophic loss of air, you would not reach the tank at 5m (even if buddy breathing or with gas donation).

 

[Dody]

I'm assuming the DM was being supervised by your Deep Diver instructor and the instructor was somewhere nearby? I'm PADI, so I don't know the SSI course.

Congratulations and thanks for sharing!

The instructor prepared the dive but he was not on site. We dived with the DM only although I don't know what his certs are in addition to being DM. We have made all our training (OW, Perfect Buoyancy, Science of Diving, React Right that includes first aid, CPR and Oxygen Management) and fun dives with him and/ or the instructor and we are very confident that they are qualified enough even though nobody is perfect.
One thing of importance is that it is COVID time and business is tough for diving shops. No tourist. So we are fortunate to have the intructor- DM/ student ratio at 1/1 or 1/2 at most.

 

[drk5036]

So this wasn’t actually a deep dive for a PADI course correct, just one you planned and wanted to do on your own?

 

[Dody]

There is no scuba police so you can do whatever you want.
Still, ascending while horizontal increases vertical drag, making a controlled ascent easier. It also avoids that you kick divers below when ascending with a shot line.

I just asked because by the OP's description, it seemed he was taught to ascend vertically by default. I know I was and just corrected it later.



This can be done while horizontal.



These are very specific scenarios as implied by the word "sometimes". I would go as far as to guess that the first situation described accounts for a residual proportion of divers' ascents from depth.



Near the surface. This does not mean that I need to ascend vertically from 40m by default.

Right, I was taught to ascend vertically from deep with my left hand holding the LPI (that also help to protect the head), look up from time to time, stay with my buddy, make a few 360s to check the surroundings, progressively deflate the BCD and not inflate except in case of emergency.

 

[Dody]

Actually a good thing. If in a down current next to a wall actually the best thing is to get to that 45 degree angle and swim away from the wall into open water as the down current will decrease as you get distance from the wall. Putting air into your BCD in a down current also helps as some down currents are not super strong and using your BCD is what it is designed for. Just think of the down current as extra weights. Of course as you ascend you can dump air as required. We all need these experiences on dives to help us build up knowledge so we don't panic when in a stressful situation.

If you use the BCD to do your ascent you don't need to exert yourself and use fins to guide direction rather than have to swim up. Less swimming less air consumption.

Yes, I will keep that in mind. When I (rightly or wrongly) assumed that we were not ascending fast enough, I should have inflated our BCDs. I thought about it but I actually fought against doing it for fear of a runaway ascent. Narcosis???

 

[Dody]

Skipping the kneeling on the bottom as it was already beaten to dead...



Why were you supposed to be vertical while ascending?



Fin pivot is still taught in scuba courses?!

Obviously . I started nov 3rd, 2020 and fin pivot is now a ritual for me when I can.
From 20 m, I either ascend vertically with my left hand holding the LPI extended and protecting my head or I do it horizontally like a base jumper.

 

[Dody]

@Dody, rereading your description there are a lot of red flags (such as deco dive to 40m with a 12L of air - the second cylinder was not with you).

I would work on the basics before considering a tech course in the near future.

This was not a deco dive. But I agree that it could have been if everything had gone wrong. What do you mean by BASICS?