Recreational Scuba Deco Diving

[tursiops]

A friend of mine recently had his reg start breathing water. He had no octo and was alone. Made a quick trip up from 140.

Yep. The octo is an alternate second stage, just as useful to you on a solo dive as it might be to a buddy on a buddy dive. There is a reason a redundant second stage (preferably connected to an independent gas source) is mandatory for solo diving certification.
But this is new thinking.....not known or taught many years ago, so probably not appropriate for this retro-thinking thread.

 

[Storker]

Yep. The octo is an alternate second stage, just as useful to you on a solo dive as it might be to a buddy on a buddy dive. There is a reason a redundant second stage (preferably connected to an independent gas source) is mandatory for solo diving certification.
But this is new thinking.....not known or taught many years ago, so probably not appropriate for this retro-thinking thread.

Not to mention that it's rather nice to have if you choose to use your 2nd to fill your dSMB.

I've never donated gas outside training or drills, but I sure have had use for my secondary 2nd on other occasions.

 

[scubadada]

I do light backgas deco on about 5% of my dives. Nearly always less than 10 min, a couple longer. I don't care at all about what others on SB think about my practice

 

[boulderjohn]

I am going to write another big picture post that might explain some of the attitudes here.

The National Speleological Society sends out a publication every couple years called American Caving Accidents. They cover all manner of cave accidents, including diving accidents. I research and submit most of the reports on those, and I just sent in a couple yesterday. I want to write about one of them with enough vagueness that only a few people will know the incident. What actually happened in the incident, as in many such cases, cannot be known for sure, but those who were there for the recovery tossed around their thoughts, and as I talked to them and put it all together, I think I have a pretty good sense of what actually happened.

Two divers entered the cave with a plan of completing what is called a circuit, in which divers include a circular path as part of the dive plan. They knew that a line that leads off to the side (a jump) turned back and led back to the mainline closer to the entrance, so they were going to leave the main line, follow the side passage, and thus return to the main line. The path did not cover a long distance, so it would not take long to do it.

The two were not cave trained, but what difference did that make? One of them was an open water instructor--how much more training can you need? It was not a long dive, so their single, back-mounted AL 80 tanks would be plenty, and in case they needed more gas, the instructor was carrying an extra AL 80 slung on his chest. No problem.

The idea of the circuit makes sense, but there are reasons circuits are not included in standard cave training until the last sessions before full cave certification. They did not know, for example, that you need to verify the circuit before taking it. They also were not trained in kicking techniques appropriate to high silt cave environments, so they stirred up a bit of a storm following the jump line and probably could not see clearly when they came to the unexpected "T" intersection in the jump line. Which way to go to the main line? Well, they knew the main line was considerably higher up than the jump line, and they could see that one line went down and one line went up, so they took the one going up.

As they went along, their kicking produced even more silt, and the cave was getting narrower and narrower and narrower. They weren't expecting this. They did not know they were not heading toward the main line but were instead heading into a tight, silty, loose rock side tunnel accessible only by sidemount divers. They had to push through that mud under the low ceiling, and the line they were following got entangled in the lead diver's slung AL 80 and broke, so he dragged it along with him. Eventually they came to the end of that broken line and a wall. They finally realized they had taken a wrong turn, and they struggled to turn around. At that point the visibility was zero, and the diver now in the lead had no line to follow, since it was all in a wadded entanglement in the other diver's slung AL80. That slung AL 80 was not doing that diver much good, because he was now wedged in so tightly that he could not reach the regulator there as both divers' cylinders emptied.

MORAL: Technical dive protocols are designed to make technical dives safe. In general, the people who take classes and learn those protocols are reluctant to tell untrained people they can feel free to go ahead without that training.

 

[Angelo Farina]

Angelo the old tables had a serious flaw. They were developed for young healthy navy personnel. A diver followed me into a wreck to film us working. I went 5 minutes ahead of him and he left the bottom 3 minutes before me which left me with 8 minutes more bottom time and I was working. We both did the same deco. 15 minutes after getting in the boat he lost the use of his left arm and within 5 minutes he was paralysed down his left side. We dressed him and brought him back in the water for an hour and a half emergency deco. Back on the boat he said he was fine but 2 hours later he had to be brought to the chamber for Oxygen recompression where he recovered.

Really sorry for your buddy.
The episode looks to me as a typical "undeserved DCS", which can always occur wathever tables, computer or algorithm one employs. A common cause of these episodes are unknown medical conditions, such as pervious oval foramen in the heart.
I know very well that the US Navy tables were tuned for healthy Navy Seals. In fact the deco procedures which were taught to me in 1975 did adopt some additional safety. More precisely:
1) The ascent speed was reduced from 18 to 10 meters/minute.
2) the dive time was evaluated AFTER ascending to the first deco stop, instead of being evaluated at the moment one starts ascending.
3) After completing the required deco stops, an additional safety stop of 3 minutes at 3 meters was added, followed by a very slow ascent to surface, taking other 3 minutes (1m/min).
4) The max depth was always taken into account coupled with the total dive time, even if just one minute was spent at the max depth.
5) As a general rule one had to make just one deco dive each day. A second dive was allowed after several hours but at max depth of 10m (where NDL is infinite). And often we did employ an ARO (pure oxygen CC rebreather) for this second dive.
There was no Nitrox. But in any case it had been not very useful, as most deco dives here in the Mediyerranean were deeper than 40 meters.
The point relevant to the original post is that here a lot of people continued to dive this way, using a large tank filled with air, and using it also for some short deco stops.
The advent of computers just made it easier to dive this way. One does not need an advanced tech computer, as even my basic Cressi Leonardo, costed 99 eur, provides reasonable indications for doing a proper amount of deco stops in air.
A small number of divers moved to tec diving, using trimix for going deeper (the rec limit with air is around 50m) and using a different mixture for accelerated deco.
But most rec divers, as me, feel no need to step up to those tech levels.
We are just happy diving our properly sized tank filled with plain air, going to just 40 or perhaps 50 meters, and spending a few minutes of deco stops while ascending.
We were all trained for this, we have the proper equipment and procedures, and so I can confirm that a lot of people here in the mediterranean sea dive this way. It is not a small niche, it is quite standard here...
Not in Padi diving centers, perhaps, but here there are a lot of other agencies.

 

[Angelo Farina]

A friend of mine recently had his reg start breathing water. He had no octo and was alone. Made a quick trip up from 140.

I also do not usually employ an octo. I much prefer to carry a fully independent second reg..I think it is safer...
l also never dive solo. And I think that rec deco dives can only be done diving in strict buddy couples, not solo. This is how we were taught, and is written in our certifications...

 

[Gareth J]

Two possible explanations:
- The members seem mostly US based. US agencies teach no-deco or are then (mostly) focused on accelerated deco. And, possibly from skipping the light backgas stage, US divers may not be doing the math on the limited saving from accelerating what is already a small deco amount, if we are in the light deco realm. People who took accelerated deco likely have O2 available near them.
- The UK does teach backgas deco as the natural progression, and the few of them chimed in.

Your description reads like backgas deco, possibly light.

For me,

1. Never, as not qualified by any of the classes that teach it.

The light backgas deco classes are mildly appealing. I think I might use it on occasion on the fly, provided I had ample independent reserves. Such as with the dive planned principally as no-deco but with a backgas deco variant. My normal rig is sidemount, so I have independent air. AN/DP provides more options though.

If deco was the principle plan, I might stay longer and carry 50 or 100% if it was available, so not RSDD. If no O2, I could see doing a planned light backgas deco dive, obviously given contingency gas, thermal, etc.

2. Shore
3. Salt
4. Solo mostly
5. Sidemount doubles. (Backgas is a good enough term, the meaning is obvious.)
6. Depth, cold level. I'm far from the NDL.
7. Sightseeing

Unusual insight.

We where expecting to run some SDC's this year (Skill Development Courses) the C-19 has messed that up (rather like the whole seasons diving).
One would have been an O2 Admin' course, the second an ADP course. We ran a Twinset course last winter for some of the newer Sports Divers.
What diving we did get in last year included a trip to "Mull" (Sound of Mull - Scotland), Every day at least one of the dives would have been compulsory staged decompression. Half of those on the boat either had an ADP, ERD or Trimix qualification. The rest, just held the basic Sports Diver diving qualification.
Those who had a decompression gas, saved it for a couple of specific dives. The majority of diving was on air (other than the Nitrox some arrived with).

So most of the decompression was on air. This was a logistical issue. The boat had a compressor. Where we where staying had limited O2, they where not going to get O2 in specially for us. We where there between lockdowns. (I was Ok if they could give me a top of O2 at some point for the CCR). Carrying cylinders on and off the boat would have been a bit of a pain as well.

For the most part, it was recreational. i.e. less than 15 minutes of deco, 35m max with one exception. The Rondo, which some dived to the bow (50m) and ran longer decompression, unique in that she is almost vertical, with the stern in 5m.
The kit was twinsets (stages on the Ronda), singles with pony's. One diver on a 15 litre without pony, and me on a CCR with a ali' 80 of 27%. The diver on the 15 was the weak link.

As I previously said, this was 'easy' no stress diving at the end of a really poor season of missed dives. As others have stated, many agencies include decompression diving in their basic diving qualifications.

 

[scubadada]

A new poll for me

 

[KenGordon]

Of course, if you want to go all the way back to Navy tables, there’s nothing that stops you from doing it. But you can’t mix RDP and deco. And you can’t mix training that has at its core “If all else fails, go to the surface“ and deco. It was eliminating deco that made those other practices safe. If you re-introduce deco, you have to also make changes to address your changing assumptions.

I don’t think RDP features in any of the diving being talked about in this thread, or indeed at all outside training.
In the U.K. we used Royal Navy tables until BSAC commissioned a set of tables exactly for recreation (Ie fun) deco diving in 1988. Those are also for square worst case depth profiles but try to make repetitive diving a bit better. Once computers turned up the fact that the dive was to 37m and not 39, and only at 37 for a short time and averaging 34 could be taken advantage of to reduce deco time. Similarly I don’t think a direct ascent is taught to people that you expect to do deco. In BSAC we certainly do not, it gets a mention of about a paragraph in the context of better bent than drowned. Does anyone expect a 4 minute 40m NDL dive with a OOA forcing a direct ascent to the surface to be perfectly ok? Does an extra couple of minutes at depth make it suddenly dangerous or was it always dangerous?

MORAL: Technical dive protocols are designed to make technical dives safe. In general, the people who take classes and learn those protocols are reluctant to tell untrained people they can feel free to go ahead without that training.

Was somebody suggesting that untrained divers should be doing deco?

For backgas single cylinder deco the BSAC Sports Diver course explains how to plan the dive with respect to gas consumption, stop times, oxygen toxicity etc. It also includes theory about redundancy, so the use of a pony or twinset, and why that is desirable.

There is a big cultural gap between the likes of CMAS, BSAC and other grass roots organisations and the commercial agencies. In a club based system the idea is to enable people’s diving. If people want to dive a bit deeper or a bit longer they find ways to do it, they want the simplest solution, probably based on what they already do. If you say “now you need a twinset, a stage, a source of o2, an extra 5 days of training and some extra regs” to spend a week in Scapa or just to get reasonable bottom time on a second dive they will ask why and whether there is a simpler way. Of course, for a shop that is an excellent sales opportunity.

 

[Angelo Farina]

From the latest posts of @Gareth J and @KenGordon I see that the situation in UK is very similar to Italy, and, I suppose, to France, Spain, Greece, Croatia, and possibly the rest of Europe.
Here these light-deco dives, breathing plain air, are normal in a fully recreational context, and are taught since the first-level course.
As said, it is not a small niche, it is the standard way of diving here.
The small niche is tech diving with accelerated deco (in pure oxygen or high-Nitrox), and perhaps trimix.
This requires additional training and difficult-to-find logistics for getting these special mixtures.