Reasons to do "Minimum Deco"

[Reg Braithwaite]

So Reg, you're against traditional emergency stops?

I'm a n00b, perhaps I've already forgotten my training. Please help me out: What is a "traditional emergency stop?" I remember the term "safety stop," and also the delightfully oxymoronic "mandatory safety stop." But "emergency stop" does not ring a bell...

 

[boulderjohn]

This is a very interesting and controversial topic that could produce an interesting discussion in the Ask Dr. Decompression forum.

DAN has a lot of information on different studies on ascent rates and stops. I believe I can summarize most recent research as advocating direct ascents to specific levels and then staying at those levels for longer periods of time.

 

[boulderjohn]

This article might be helpful:

DAN Divers Alert Network

 

[Reg Braithwaite]

This article might be helpful:

DAN Divers Alert Network

Fascinating! The opening two paragraphs:

Although decompression tables have been significantly modified over the last 20 years, with many now giving much shorter times at depth than the original U.S. Navy tables, the incidence of decompression illness (DCI) has changed very little. Even the recent introduction of dive computers has not made a significant impact on dive injuries.

Decompression illness incidence remains consistent with the distribution for sex, age and training among divers, regardless of the computers or tables they use. The problem, as previously elaborated in Alert Diver appears to be a too-short time of ascent; this is the only parameter that has changed very little over the last 40 years and, accordingly, appears to possibly be the real controller of the incidence of DCI.

 

[HenrikBP]

I'm not sure this is appropriate to "Basic" scuba discussions, but in the "basic" world of recreational diving, I think the benefits would be so minor as to be statistically unmeasurable.

Nothing wrong with pointing out that NDL is a bit of a misnomer IMO ...?

As for anecdotes; mine is that I found that I was much less tired after I got better at slowing down my ascents and holding stops. I've heard others mention similar experiences.

Minimum Deco ascents really doesn't take much more time; in Fundies we were shown that for a 100' dive you end up spending about 1:30 minute more (8 minutes total) doing a Min Deco ascent than you would doing the standard Rec 30'/min plus 3 minute "safety stop" (~6:30 - 7 min). If you choose to further slow down the last 15' of the ascent, the difference is less.

Henrik

 

[mikemill]

"Minimum Deco" is the most common name given for a practice of making a very slow (10ft or 3m per minute) ascent from approximately one half of your average depth on dives that most people would call "No Deco" dives. Another name you'll see is "One Minute Ascents" (which I find incredibly misleading since you take much longer than a minute to make the complete ascent!

The usual practice is to stop for about thirty seconds and take 30 seconds to ascend 10ft/3m, stop for thirty seconds, and so forth. On another thread, some asked why it was worth the bother...



Reasons I choose to do Minimum Deco (or something approximating it):

• Provided that conditions are pleasant, off-gassing in the water is better than off-gassing on the surface.
• If I overstay my welcome and need to do some actual deco, I already know how to do it, I just need to adjust my schedule.
• A n00b like myself can never have too much practice maintaining level trim at a constant depth without kicking.
• I paid for a full tank of gas, why not use it?
• There's something meditative about hanging stationary and weightless. Why pay a yoga studio for the experience?
• I'm also "trained" for recreational trimix diving, which is much less forgiving of fast ascents and blowing off "safety" stops. Why not use one protocol for all of my dives?
• You can never have too much practice launching an SMB and keeping the line from wrapping around your throat. Especially if your 'home turf' is the swift running St. Lawrence River.
• Anecdotally, reduces sub-clinical DCS instances without the expense and hassle of diving nitrox. Combine with nitrox for ridiculously safe diving.

That being said, on drift dives you really want to stay with the group. If they're following the "standard" protocol, you have to start your deco before they do to surface in the same place at the same time. Also, in certain situations you can drift into trouble while doing minimal deco on an SMB, like a shipping channel. You have to plan accordingly and maybe do your deco on a wall or while swimming gently to navigate appropriately.

On several dives in Cozumel I bailed a little early and did my first couple of stops swimming slowly above the group while observing them poking around the reef from above. They then ascended to 15' while I was at 20' and everything worked out just fine.

Bailing early is also only appropriate if you are comfortable doing this solo. In the St. Lawrence, I am not. In Cozumel, I was.

You forgot fun. I seriously have had more fun on ascents doing min deco then the three minute safety stop.

Another reason for min deco is that it simplifies the NDL table. Part of min deco is that after a 1 hour surface interval the whole thing resets. That means I just need to know the NDL table which is a simple depth=>time relationship, follow the min deco procedure, and take a 1 hour SI. No need to figure out what pressure group you are in, residual nitrogen levels, etc.

 

[Reg Braithwaite]

You forgot fun. I seriously have had more fun on ascents doing min deco then the three minute safety stop.

Absolutely correct, sir!

Another reason for min deco is that it simplifies the NDL table. Part of min deco is that after a 1 hour surface interval the whole thing resets. That means I just need to know the NDL table which is a simple depth=>time relationship, follow the min deco procedure, and take a 1 hour SI. No need to figure out what pressure group you are in, residual nitrogen levels, etc.

Well in truth I was trying to keep this to the discussion of why I adopted this particular ascent strategy without getting into how one calculates the limits of when it can be applied (namely that given a certain average depth, what is the longest dive you can execute and still use this strategy?)

As it happens, I wound up using a hybrid strategy last Friday: We asked the dive operator to take us to a "deep" dive in the afternoon after executing the usual deep/shallow two-dive morning combo. The operator's response was that we would only be permitted to do it if we had computers and dived within their limits.

I wasn't about to start THAT conversation with them, so I pulled out the computer I use as a backup BT and used the "plan" mode to demonstrate that it was perfectly happy with the proposed dive. And indeed, it didn't complain during the dive either.

 

[Mr Carcharodon]

Another reason for min deco is that it simplifies the NDL table. Part of min deco is that after a 1 hour surface interval the whole thing resets. That means I just need to know the NDL table which is a simple depth=>time relationship, follow the min deco procedure, and take a 1 hour SI. No need to figure out what pressure group you are in, residual nitrogen levels, etc.

That is a really good point. Min deco, especially with the 120 rule (or similar) thrown in is much simpler than the convoluted mess that dive tables present. Listening to your body and adjusting your deco accordingly seems to be more reasonable than the more prevalent approach of adding ever more padding to deco schedules without giving any thought to other factors that may apply.

 

[Reg Braithwaite]

That is a really good point. Min deco, especially with the 120 rule (or similar) thrown in is much simpler than the convoluted mess that dive tables present. Listening to your body and adjusting your deco accordingly seems to be more reasonable than the more prevalent approach of adding ever more padding to deco schedules without giving any thought to other factors that may apply.

One of the more interesting points from the article linked above (and which I quoted) suggests that padding the tables has had no effect on DCS incidences. The variance seems to come form how we manage our ascent.

Perhaps Minimum Deco is more optimal than safety stops, perhaps not. But how we end the dive seems to be much more important than it would seem given the emphasis on tables and NDLs in the popular recreational training.

 

[Sloth]

One of the points of GUEs rec to tech mantra is "starting with the end in mind". In the spirit of that another advantage to doing Min Deco is it helps you grasp the concepts of controlled ascent rates needed for deco diving later on down the road.

Yes this is a basic scuba section but GUE and UTD both structure their rec programs as stepping stones to tech. Always need to factor that in when you question why things are done at the recreational level by these agencies.