Past NDL. And then this???

[Dan G]

Ladies and gentlemen,

The horse (OP) is not dead as yet and ready to be beaten AGAIN (maybe I’ve started enjoying it).

I did look at all “official” resources I have about emergency decompression procedures (as PADI calls them).
Here is the list with a brief description of the procedure on each:
- PADI OW manual: If a computer is used, follow the computer. If a table was used follow the procedure described in the table.
- The PADI OW tables: If NDL elapsed by up to 5 mins, 5 minutes deco stop at 3-5 meters, if NDL elapsed by more than 5 mins then 15 mins deco at 3-5 meters (no word on calling the dive or min rate of ascent).
- My Computer’s manual: it only describes what is shown in the screen. Not what/how to do. Yes there is a TOTAL time (including ascent time) but that is an “indication” as clearly stated. Neither a requirement nor even a suggestion!

My question: based on the above, how am I (or any other newbie diver) supposed to know that once in emergency deco, I should ascent ASAP to deco?? Is it just too obvious to everybody else but not me? In that case please beat me, hard!

Through the discussion, and thank you all for this, it is now clear. But how the heck was I supposed to know that before the incident?* Since it is so vital, shouldn’t it be mentioned clearly in the manuals? Eg In case of emergency deco, call the dive and ascent as soon as possible (<10m/sec) to the first deco stop following your computer’s instructions.

Please hold on beating for a sec – I promise you (I) will get more soon.

Now something else, very important for fellow newbie divers with Leonardo (and maybe other Cressi computers) to observe!

As discussed in another post my computer has an ascent rate indicator. Up to 3 arrows are displayed: one arrow for 4-8m/sec ascents, 2 arrows for 8-12m/sec and 3 arrows with a beep alarm for >12m/sec.** So far, so good. The problem arises when the dive is imported to Subsurface. Cressi records all of these as “type=3” events, i.e. warnings. Hence all these ascents (1, 2 or 3 arrows) are marked as warnings (yellow triangles) in Subsurface! Yes an ascent rate of let’s say 4m/sec is reported as a Warning in Subsurface!

Prepare your canes – beating time approaching.
Believe it or not, silly me, all this time, this has led me to assume that even a single arrow ascent (4-8m/sec!) is to be avoided.
Beating can now start again.

All I hope is that this post to reach as many (idiot?) newbie divers as possible to avoid all these silly mistakes.

Thanks once more...

My perspective is that of a recreational diver who has only just over 200 dives, so I can relate to your perspective of being new and not knowing tons of stuff. Look above for what I put in bold. I have learned a lot from this thread, so thank you for posting and keeping with the thread.

*I would say that much of your learning depends on the people you dive with. We often model the behavior we see in others when learning something new, so hopefully we find good people to copy. I think a good recreational dive briefing includes something like this: "This is a no-deco dive. We do not want anyone going into deco. If you get to 10 mins of NDL, I want to know so get my attention by any means possible, point at your computer and hold up the number of minutes of NDL you have." (or something similar to this.) If there is no guide in the water with you, then the buddy teams should be have this worked out for themselves.

The guide or buddy team should have procedures worked out in advance about how to respond and the signals they will use. Will everyone ascend? Will just the buddy pairs ascend? Some of this depends on the type of dive. Moored boat? Drift? If drift, how many buoys do you have?

As a new diver I would say it's important that the experienced divers in your group know all of this stuff and teach you by example. That is how you are supposed to know, especially if you were not taught in your OW certification.

**This doesn't seem right to me. 4-8m/sec is approximately 12-24 feet/sec. That's too fast.

 

[w3dge]

**This doesn't seem right to me. 4-8m/sec is approximately 12-24 feet/sec. That's too fast.

I'm assuming the OP meant 4-8m/minute

 

[stepfen]

**This doesn't seem right to me. 4-8m/sec is approximately 12-24 feet/sec. That's too fast.

m/sec was a mistake in my initial post. m/min is the correct

 

[tursiops]

- The PADI OW tables: If NDL elapsed by up to 5 mins, 5 minutes deco stop at 3-5 meters, if NDL elapsed by more than 5 mins then 15 mins deco at 3-5 meters

Not quite.
If NDL is exceeded by 5 mins or less, then ADD 5 mins to your normal 3 min safety stop, i.e. 8 minute stop.And stay out of the water for 6h (to monitor for DCS).
If NDL is exceeded by more than 5 mins, then MULTIPLY 5 mins by your normal 3-minute stop, i.e. 15 minute stop.And stay out of the water for 24h (to clear your tissues).

 

[sea_otter]

Stepfen, you're a good sport.

Best recommendations I can offer (beyond what already has been beaten to death):

• Step 1 is to COMMUNICATE. Give a thumbs up to let your buddies know you are aborting the dive. You can also optionally explain why (point to or show your computer, put a pinky finger up to signify deco). But the important part here is to make it clear that the dive is done (rather than swimming slowly along back up the reef to the boat).
• Ideally, your ascent speed would be approx 10m/min for the deepest part, slowing to 3-6m/min shallower. However, this is hard to do, and given the depth you need to traverse, exact speed isn't so important. Keeping everything in control is critically important. Aim to keep the ascent rate at least at 1 arrow. You can go to 2 (especially for the deeper part) if you like, provided you have the ability to put on the brakes. Avoid going to 3.
• When you reach the stop depth, again, communicate. Give a level off signal. Make sure your buddy knows what's going on. Hang there and wait for the computer to clear. It should be counting down here.

Of course an ounce of prevention is worth a pound of cure here, so if you see yourself low on NDL, communicate that fact to your guide or buddy. Ask to go to a shallower depth. We all want to swim around enjoying the pretty fish as long as we can rather than sitting under the boat.

 

[stepfen]

Not quite.
If NDL is exceeded by 5 mins or less, then ADD 5 mins to your normal 3 min safety stop, i.e. 8 minute stop.And stay out of the water for 6h (to monitor for DCS).
If NDL is exceeded by more than 5 mins, then MULTIPLY 5 mins by your normal 3-minute stop, i.e. 15 minute stop.And stay out of the water for 24h (to clear your tissues).

Deco stop time is on top of the safety stop. Anyway, the exact times are not the point of my post. The point of my post that calling the dive and ascent asap to deco depth is nowhere mentioned.

 

[stepfen]

Guys I think the procedures, need for communicaiton etc have been discussed over and over again and are now very clear. I am now discussing two other important (according to me) things:

A) Once in emergency deco, calling the dive and going up to deco depth FAST is so important step but it is not mentioned anywhere in the manuals, and
B) Cressi (and hence Subsurface) marks any ascent faster than 4m/min as a warning

 

[Miyaru]

....
I did look at all “official” resources I have about emergency decompression procedures (as PADI calls them).
Here is the list with a brief description of the procedure on each:
- PADI OW manual: If a computer is used, follow the computer. If a table was used follow the procedure described in the table.
- The PADI OW tables: If NDL elapsed by up to 5 mins, 5 minutes deco stop at 3-5 meters, if NDL elapsed by more than 5 mins then 15 mins deco at 3-5 meters (no word on calling the dive or min rate of ascent).
- My Computer’s manual: it only describes what is shown in the screen. Not what/how to do. Yes there is a TOTAL time (including ascent time) but that is an “indication” as clearly stated. Neither a requirement nor even a suggestion!

My question: based on the above, how am I (or any other newbie diver) supposed to know that once in emergency deco, I should ascent ASAP to deco?? Is it just too obvious to everybody else but not me? In that case please beat me, hard!

This what you find in the book (or on the internet). An instructor teaching this, will explain the details and answer questions that come up. I think you just perfectly illustrated why you cannot learn how to dive by just reading texts.

I don't know what your instructor taught you during your open water. I always address this issue when explaining NDL limits. After explaining why you shouldn't cross them as a novice diver, I also explain what happens if you do. It's not in the books. I took pictures of a dive computer during a dive where I crossed the NDL, and show my students what's on the display during ascent and how it changes from ascent time to stop time.

When you're a novice diver, it can be called an emergency procedure, since you still lack the knowledge to deliberately plan and make a dive beyond the NDL.
But that horse has been beaten in this topic.

 

[Miyaru]

Guys I think the procedures, need for communicaiton etc have been discussed over and over again and are now very clear. I am now discussing two other important (according to me) things:

A) Once in emergency deco, calling the dive and going up to deco depth FAST is so important step but it is not mentioned anywhere in the manuals, and
B) Cressi (and hence Subsurface) marks any ascent faster than 4m/min as a warning

Your ascent rate depends on the depth. In the deeper part of a dive, your tissues are still on-gassing and a slow ascent will increase the stoptime. To start offgassing, tissue pressure must be higher than the ambient pressure, and from this point onwards the ascent speed does matter. But that's part of a course for decompression diving.

When you're at 25m depth, and your computer tells you to ascend to 3m during 8 minutes, you ascend with approximately 3m/min. Determining your ascend speed is not easy, and when you're unexpectedly in a situation where you have to do this, stress will make it even more difficult.

 

[tursiops]

Deco stop time is on top of the safety stop. Anyway, the exact times are not the point of my post. The point of my post that calling the dive and ascent asap to deco depth is nowhere mentioned.

Actually, it is mentioned in earlier editions of the PADI OW manual.I suspect it was removed in the most recent edition because it was thought to be an unnecessary statement. Apparently not.