Going into deco

[Thalassamania]

Tabus around deco diving are very much an American hang-up probably due to the certifying agencies based there and their fear of litigation. Interesting to note that my PADI & SSI tables stop at 39m while my CMAS tables cover both longer dives with more stops and dives to 63m. It's probably also a commercial thing because by imposing limits there is room to sell a lot more courses.

There are places I visit with a lot of wrecks in the 30-40m range where deco diving according to the tables (nice square profiles) and on singles is absolutely routine and I've never heard of any incidents. Most of my friends in the UK regularly dive deco. Attitudes seem to be a little different on the other side of the Atlantic.

I think that you'll find the difference in attitude has an historical basis. All scuba in the USA tracks back to Scripps in the early 1950s. Planned decompression diving always required approval by the Diving Control Board, from even the earliest days. All the recreational programs in the USA grew out of that tradition and thus planned decompression diving was not a commonly accepted thing.

 

[String]

Most of my friends in the UK regularly dive deco. Attitudes seem to be a little different on the other side of the Atlantic.

The general attitude here is if you end up with some deco, so what? Whereas PADI and co seem to teach that clicking into deco by 1 minute you'll die horribly but running the 1 minute NDL left line the other side is fine.

A few reasons its accepted in the UK, firstly the good wrecks are deep enough that some deco is wanted to see them properly.
Secondly, all the club based agencies (probably a majority of diver training in the uk) be it BSAC, SAA,ScotSAC all teach mandatory deco as part of the main syllabus. BSAC teach it in sports diver, the level 2 qualification for example.
The result is a loads of divers not scared of deco who quite happily do some if needed.

 

[Ryan96]

There are places I visit with a lot of wrecks in the 30-40m range where deco diving according to the tables (nice square profiles) and on singles is absolutely routine and I've never heard of any incidents. Most of my friends in the UK regularly dive deco. Attitudes seem to be a little different on the other side of the Atlantic.

I've been diving in Beirut, Lebanon for a little less than a year now and all our diving is what I might call "recreational deco" - the wrecks and decent reefs tend to start in around 32m and extend down into the 50's. So all our recreational dives are pretty close to square profiles in the 34-40m range. On the air-only dives, we usually end our dives when we hit 3-5 min deco on our computers and make a direct ascent to our deco stop(s).

On these direct descent dives we usually do our deco obligation around 9-10m then follow with a safety stop at 5m. I'm was about to start incorporating Pyle/deep stops at 1/2 depths on my way to the 9m deco stop and an instructor told me he thought he read recently that some studies had been done that showed that deep stops were not reducing bubbling and that all deco obligations (short ones typically recommended for <10m) should be done at 10m for minimum bubbling.

Anyone heard of this? Who out there who does "light" deco regularly (not necessarily full-on tech diving with deco mixes) is using deep stops? Where do you generally like to do your 3 or 6m deco obligation - @ 3/6m level or deeper?

Ryan

 

[DeepBound]

Anyone heard of this? Who out there who does "light" deco regularly (not necessarily full-on tech diving) is using deep stops? Where do you generally like to do your 3 or 6m deco obligation - @ 3/6m level or deeper?

Ryan

I learned to do some 'light deco' on my Apprentice Cave Diver course, but this involved some limited training in decompression techniques, and we would use a high-02 deco gas for the decompression. They also recommended getting full decompression training.

I've always thought of deco as being the main issue that separates tech from recreational diving, along with depth. Just curious, why did you consider these to be recreational deco dives?

One of the things I learned about even light deco is that decompression should always be done with a high-02 deco gas. Decompressing (intentionally) on back gas is just not a smart thing to do, at least according to my instructors.

On the cave course we would do a regular 30ft/min ascent to 20ft and do the stop there. It was more conservative since the computer would make you do more time at 20ft than at 10, and the gradient would be lower at the depth.

 

[Ryan96]

I've always thought of deco as being the main issue that separates tech from recreational diving, along with depth. Just curious, why did you consider these to be recreational deco dives?

Becasue as far as my knowledge of diving physiology goes (and as other posts have pointed out), the practical difference between 3 minutes deco @ 3m and the NDL is marginal at best. On some tables/algorithms the same dive may have generated no deco. It's a gradient. I think from a safety perpective the situation is markedly different if I have 30"+ of deco obligation compared to 3".

One of the things I learned about even light deco is that decompression should always be done with a high-02 deco gas. Decompressing (intentionally) on back gas is just not a smart thing to do, at least according to my instructors.

Well again physiologically I'm not sure this is necessary. The high 02 gas is accelerating the process but I don't see why deco on 21% for a little longer in the shallows is fundamentally unacceptable. I haven't been able to find any research that discusses this but a lot of divers here (trimix intructors included) do these types of profiles (typically with non tech divers) with short deco stops on air. I generally finish my "light" deco dives here with around 85-90bar (on a 12L tank) - having enough gas for the stop isn't ever an issue. (Sorry for the metric/bar units but I dont remember the conversions)

On the cave course we would do a regular 30ft/min ascent to 20ft and do the stop there. It was more conservative since the computer would make you do more time at 20ft than at 10, and the gradient would be lower at the depth.

I agree that doing stop a little deeper to reduce the gradient pressure seems to make sense even if it means a little longer stop. The whole point of the deep stops seems to be taking this idea a little further. Was curious what others are doing ...

 

[waynel]

Lynne, I'll betchya that Peter did a reverse profile (going deeper on the second dive than on the first) ... Suunto computers penalize you heavily for doing that.

I go into deco regularly (according to my Vytec) ... all I do is come up very slowly from 60 feet ... spending progressively longer intervals at the 40, 30, 20, and 10 foot levels. The computer is usually satisfied long before I am ...

... Bob (Grateful Diver)

Yep. Sunnto's are all conservative and unforgiving, and my Gekko is probably the most conservative of the bunch. In fact, I once had a DM on a wreck dive assign me to track the dive because I had the most conservative computer in the group.

 

[Sharky1948]

Is this the right signal for D? According to this, the sign for D is index finger pointed.
http://en.wikipedia.org/wiki/American_Sign_Language_alphabet

Just wondering if your recommendation is universally known, or something that you and your dive community have come up with.

The pinky is generally considered the sign for deco. Either followed by fingers for the number of minutes, or a crooked indexed finger for question. (It's not the ASL sign for "D".) Here's a link to some videos of U/W signs if you're interested: http://www.dayoscuba.com/ (There is a link near the top on the right.)

 

[DeepBound]

Becasue as far as my knowledge of diving physiology goes (and as other posts have pointed out), the practical difference between 3 minutes deco @ 3m and the NDL is marginal at best. On some tables/algorithms the same dive may have generated no deco. It's a gradient. I think from a safety perpective the situation is markedly different if I have 30"+ of deco obligation compared to 3".

It's unfortunate that the different tables and algorithms vary so wildly, giving the impression that its all very grey and unknown. The idea behind an NDL dive is that divers without a lot of experience or training still have the option of punching out and swimming to the surface if they aren't in deco. Even if the line is fuzzy, it has to be drawn somewhere. I think its important to make a distinction between a dive where you can, if necessary, bail out, and one where bailing out may mean going for a chamber ride. I believe that with even a liberal computer that says I haven't reached my NDL, I can swim up at 60ft/min in an emergency without expecting to get bent. Not something I recommend or plan to do, but once you cross that line to a dive where you absolutely can't do that, you're doing a different kind of dive, which requires a higher degree of training and confidence, that not all recreational divers have.

I think even the liberal computers have enough safety built into them that you can do that kind of bail-out to the surface without getting DCS. That's what they claim, and they know they'll get sued if their algorithm is wrong. The grey fuzzy area is when you get into light deco, where you might or might not get bent if you bail out.

 

[diver 85]

The VEO gives suggested safety stops. Do you know the difference between that reading and a Deco Required reading?

I'm not going to try to tell a veteran diver how to dive, but I do encourage newbies to study their manuals and computers until they know them very well - hide the card so you won't try to use it, and run Simulations.

.............lol........Well, afterall, it was a computer & satisfied Aldora's requirements......In a nutshell, new divers(IMO fewer than 5 yrs or less than 300 or so dives--it takes some people a long time to get it right--)are making this dive thing way too hard......(you would not have wanted to be on our first 6 dives in Belize in 'Dec of '85, all led & 'guided' by a DM---I'll just leave it @ that)....

Whoops( & forgot to add) ALL dives are deco dives if you make a SS.......

 

[Ryan96]

DeepBound, I really do respect what you are saying. And believe me I don't think the tables/algorithm are "all gray area". But I believe that that diving is always potentially dangerous and that good judgment is critical. A lot of recreational divers are woefully under-trained already and not ready to deal with the dangers which exist in non-deco diving. I've had the (unfortunate) opportunity to make 3 emergency assists, including 2 OOA emergencies. These unprepared divers were risking quite a bit while I think someone with a lot of dives who hasn't necessarily done a proper "deco procedures" course but, being who is aware of their gas consumption and the basic procedure taught in OW, who plans for a 5" deco stop may being substantially safer. I mean if we're buddy diving and following our plan we should never have to make a CESA or worse. I think dogmatically viewing the NDL as an absolute limit for "recreational" diving misses the importance of using your head when preparing for and executing a dive.

Maybe I shouldn't have said "recreational deco". But I am not a "professional" or highly trained trimix diver - I consider myself a "recreational" diver. Maybe PADI has to be dogmatic about this for liability - but I think it's pretty reasonable for experienced divers to try to navigate a bit in the gray area.

Anyway that's my 2 cents. Respect to those with other opinions.

Ryan