Decompression Stop Guidelines - What we have to do if got deco alert?

[Belzelbub]

Consequently, you have something mentioned in the origin of this thread--people being told that if they violate NDLs with a computer, they should follow the rules for violating NDLs with a table. Students taught that way can be logically excused for not searching through the manual to find out how the computer deals with decompression stops.

Good point. I hadn't considered that some may be told to revert to table if violating computer NDLs. I was only officially trained on tables. I moved to computers several years later, and while I still have some tables and know how to use them, I don't use them for anything other than a quick reference.

View attachment 752845

I dive two computers, one running DSAT and one running Buhlmann with a GF high of 95. Assuming we both have enough gas, if you are diving PZ+ or Buhlmann at a GF high of 85 or 75, you are going to exceed your NDL and go into decompression well before I would. So, we dive for an hour, is this a deco dive? For me, no, for you, yes. You should follow the recommendation by the computer you chose to dive with and satisfy the decompression obligation you are given.

This is the type of thing that should really be discussed in a dive computer based course. The differences between one algorithm to another. I'd done a bit of research prior to buying my first DC, so I knew I wasn't getting the most conservative, but I'm sure the average 1st time buyer doesn't have a clue.

 

[Centrals]

I was taught to use TABLE in my OW course yrs ago and have to spend time to learn how to calculate ndl. I wonder how ndl is being taught by using computer.

Dive computer based course and basic decompression theory should be included in AOW. It is about time that agency should extend the course. They probably have to retrain some of the instructors on both topic.

 

[boulderjohn]

I was taught to use TABLE in my OW course yrs ago and have to spend time to learn how to calculate ndl. I wonder how ndl is being taught by using computer.

Dive computer based course and basic decompression theory should be included in AOW. It is about time that agency should extend the course. They probably have to retrain some of the instructors on both topic.

I am not sure of your first question--if you want to know the NDL for the planned depth of a dive you are about to do, you go to the computer's planning function. Is that what you wanted to know?

Basic decompression theory is taught in the OW class. Are looking for something more advanced in the AOW class?

 

[Blackcrusader]

The Perdix manuals are great. Very easy to read, and easy to understand.

That's if people bother to RTFM. I was diving in the Philippines and a woman on the boat also had a Perdix AI. She was diving it in rec mode. She saw mine and that my screen had different features to hers. She had no idea the Perdix had a Tec Mode or that you could change what you wanted to see on the screen. I just told her to keep hers the way it was in the default recreational mode.

She had not read the manual. She also learned my NDL times were different to hers on the same dive together. Just having the same DC does not equate to having the same NDL times.

 

[Gareth J]

According to whom?

I don't believe I have ever been in a situation where I had two hours between NDL dives while using a commercial operation.

I just checked through this years charters. The shortest surface interval was 2:33 minutes.
That was an Ocean diver (Eqiv’ PADI OW) trip and we wanted to get away early for the return home.
The Scapa trip, all the surface intervals were over 3hours

@boulderjohn

I know this is an old thread. I thought I would follow up on our earlier conversation. I have just completed a live aboard in the Red sea, it was a recreational trip - no decompression diving. The surface interval between was never under 2 hours. Most of us did all the dives (four dives a day including a night dive). Dive times where all around 60 minutes, some times a little under some times a little over. Deepest dive 36m. Most of the wrecks are between 20 and 30m. The night dives where generally 15m or less.
(We didn't do a night dive on the Thistlegorm this time. They may have changed the rules, so it may no longer be allowed. A night dive on the Thistlegorm could potentially be over 30m).

Gareth

 

[boulderjohn]

@boulderjohn

I know this is an old thread. I thought I would follow up on our earlier conversation. I have just completed a live aboard in the Red sea, it was a recreational trip - no decompression diving. The surface interval between was never under 2 hours. Most of us did all the dives (four dives a day including a night dive). Dive times where all around 60 minutes, some times a little under some times a little over. Deepest dive 36m. Most of the wrecks are between 20 and 30m. The night dives where generally 15m or less.
(We didn't do a night dive on the Thistlegorm this time. They may have changed the rules, so it may no longer be allowed. A night dive on the Thistlegorm could potentially be over 30m).

Gareth

Just to repeat what I said earlier and repeat my earlier challenge.

I have dived all over the world and never encountered it. Ever. I do not question that you have encountered it. I question your implication that it is a world-wide norm.

The challenge: you earlier said that waiting at least two hours between NDL dives was established best practice. I challenged you to provide any established and authoritative resource that says that.

I have never seen a hint of that in any of my reading. I have taught countless OW classes in my time and taught dive table theory for most of those years. I had students work out dive plans using the training materials word wide, and most of the given exercises involved determining required surface intervals. One of the problems students were given established that the minimum required surface interval for the given dive sequence was zero minutes.

 

[ThatDogDontHunt]

Just to repeat what I said earlier and repeat my earlier challenge.

I have dived all over the world and never encountered it. Ever. I do not question that you have encountered it. I question your implication that it is a world-wide norm.

The challenge: you earlier said that waiting at least two hours between NDL dives was established best practice. I challenged you to provide any established and authoritative resource that says that.

I have never seen a hint of that in any of my reading. I have taught countless OW classes in my time and taught dive table theory for most of those years. I had students work out dive plans using the training materials word wide, and most of the given exercises involved determining required surface intervals. One of the problems students were given established that the minimum required surface interval for the given dive sequence was zero minutes.

Agreed. Each operator has their own "rules" about SI duration. I claim these are mostly based on operational procedures as opposed to following the science. The SI of any given operator is a side-effect of their operational procedures.

On the LOBs I have used recently, the SI is "generally" around 2 hours as they space the 5 dives from 8am to 7pm-ish and limit the amount of time the dive deck is open (i.e. 60 minute max dive time). The "2 hours" is based upon the operating procedure of spreading the dives out over the daily operating time of the boat.

I have been on 2 tank morning boat dives where the SI was 30 minutes with each of the dives limited to 45 minutes. The dive duration and SI was dictated by the operating procedure of needing to get back to the dock in time for lunch.

Different operators have different SI practices. SI can vary widely....

 

[dmaziuk]

30 minutes on DM's DC to "start gearing up", or 30 minutes to "pool is open"? IME the difference between the two can easily be 15 minutes and is rarely less than 10.

Not that it has much to do with topic.