NDL or deco dives

[npole]

This educational methods separating recreational from deco dives are someway estranging people from understanding the concept behind the theory.

Every dive is a decompression dive, there's no such "no deco dive", and the NDL is a misleading labeling. The ascent speed is nothing else than a *ongoing* decompression stop. The inert gases are going to fill our tissue soon after going deep, and the (limited) ascent speed is needed to have them dissolving, the "deco stops" are additional stops.

This is the reason of why it is important to stay within the max ascending speed, and that's why you can have DCS even if you're doing only recreational dives.

 

[broncobowsher]

Some computers will get pissed if you look at them too fast. I have had one that would give an ascent speed warning if you lifted it the 2 feet to your face too quickly. That little 1-button puck POS is still around. Ignored most of the time now, but lives enough to be the backup computer to one that actually works. Thankfully they realized it had issues and didn't put lockouts on it. If it locked out it would probably have been skipped across the water like a stone and allowed to sink someplace really deep.

 

[DanielRJones]

I have had to buy the same comouter as my wife to use as my backup because of the different algorithms were shutting me out when the wife was fine and also the other way around. Mine was givving longer on single or 2 dives but lagging behind on multiple dives.
I trust my wife to dive to her computer and stay safe and if that puts me into very light deco i will deal with this when it occurs. Having a backup that is the same as her computer allows me to have a rough idea on her ndls and not end up with a locked out computer

 

[scubadiver888]

I admit to be the dummest and dimmest diver on scubaboard. Took padi ow and aow 30 years ago, passed DM exam 10 plus years ago. And dumb enough when a diver asked me why his computer locked him out for a second dive from 55 ft... I did not have the correct answer three weeks ago. It is because I confused diving in the NLD means you are safe to ascend at ANY rate from ANY depth. Until I read in a deco training book that ALL divers dive using DECO procedures and rules do do decompression continuously. That breaking the recommended rate of ascend of 60 fpm early on, the 30 fpm later is the DECO time that MUST be obeyed or else you are at risk for decompression sickness, regardless of the nitrogen load your computer say. Okay flame away!!!

The No Decompression Limit (NDL) is a recreational thing. Agencies like PADI will say there is decompression diving and recreational diving. As @npole points out, all dives are technically decompression dives. If you follow recreational dive tables (or a recreational dive computer) then they indicate two things you must do. The first is a controlled ascent rate. Previously I believe it was 60 feet / minute. Then it was recommended 60 feet / minute if below 60 feet but from 60 feet to surface you should go even slower at 30 feet / minute. If you get within pressure groups X, Y or Z then you have to do a RECOMMENDED safety stop.

Some computers have things like Deep Stops and others just note if you go slower or hover at something below 15 feet but still off-gas.

Realistically, understanding how all this works and what the computer is doing is complicated. It requires the correct training. If someone REALLY wants to know then they should get some training on how to do decompression dives.

BUT you might have to read into what the divers is asking. When a 4 year asks a question, maybe the simplest answer is the best answer.

Bottom line, if a diver asked me as Divemaster why their computer locked them out, if they just wanted to not get locked out again and didn't care about the physics then I'd tell them to refer to their dive computer manual. But I'd suggest they (a) came up too fast, (b) they exceeded their NDL or (c) they didn't have a long enough surface interval for the second dive.

 

[rongoodman]

Or (d) they blew off a "required", according to the computer, safety or deco stop.

 

[scubadiver888]

Or (d) they blew off a "required", according to the computer, safety or deco stop.

Oops, missed that one.