Diving with gradient factors for a new recreational diver

[boulderjohn]

As I read through the forums and research articles, however, I come to the conclusion that using conservative gradient factors with multiple stops instead of the popular 3 minute safety stop at 5m (15ft) is a good idea for minimizing risk.

I researched and published an article on deep stops for decompression dives. I had a lot of help from renowned decompression expert Dr. Simon MItchell. When I was done, I wanted to write an article on deep stops for recreational dives, but Dr. Mitchell would not help me with it. He said there is not enough research to know one way or the other what to do. I then spent a lot of time researching on my own, and I finally concluded that there was not enough research one way or the other to know what to do.

I am familiar with the research you cite, and you should know that it is not highly regarded. The DAN America's article that originally wrote about it now has a disclaimer saying it does not represent current thinking.

What does have a lot of research behind it is the standard slow ascent--it has been investigated for more than a century. Then safety stops were added, and that made things better. The level of safety associated with slow ascents and safety stops is well-studied, and it is proven to be a very safe procedure.

If you read my article, you will see that deep stops in decompression diving used to be very popular, but more recent research has shown that they are actually harmful because of the added pressure to mid-range tissues. Perhaps a through research study on deep stops in recreational diving may show that it creates the same problem. Perhaps. Perhaps not. As I said before, the only studies that have been done are flawed, so there is no good evidence. to show either a benefit or a harm.

 

[boulderjohn]

Theoretically speaking, if you make a 30 minute dive to 90 feet breathing air and decide to make a deep safety stop at 30 feet, will you still be on gassing nitrogen? Or off-gassing?

Your fastest tissues will be off-gassing, but slower tissues will be on-gassing. Your slowest tissues will continue to on-gas throughout the dive, even during a safety stop. At that point, though, they can only on-gas to the pressure at that depth, and it has been shown that those levels are safe in all tissues.

 

[lakedog]

What do you kind and knowledgeable folks recommend for someone in my situation? Is it a bad idea for a newbie diver to try to dive with multiple stops and conservative gradient factors?

Lot's of good advice and knowledge shared. To answer your question... As a new diver, yes it's a bad idea to have this as your focus. It's great that you are trying to understand and learn but just like basic OW training to learn to dive you need more advanced training for technical diving but most importantly you need experience. Dive and dive some more. Focus on buoyancy control, practice drills, develop muscle memory, orientation, finning, knowing and safely growing your limits, etc. There are so many skills that with focus and experience will help with your longer diving journey. If your journey was a 100 steps, your on about step 5 worrying about steps 50-60.

Good luck with your diving journey and be safe.

 

[Nemrod]

After about 30 dives I've fallen in love with diving and want to pursue the hobby more actively. Unfortunately, I'm a worrying personality, risk averse, and despite being a decent swimmer and a triathlete, I'm not a natural when it comes to diving and buoyancy control. I want to find ways to enjoy the sport more safely, especially as it relates to DCS risk.

I too am a life long swimmer/triathlete and SCUBA diver. I do not overly concern myself with fear of DCS. At 67 yo and 50 plus years a diver I have never been bent and have done some pretty aggresive diving, no deco and deco adventures. I think you are overly concerned with the possibility of dcs.

I do not agree with setting air and diving Nitrox. Instead just set your computer to a more conservative setting for the appropriate Nitrox mix you are using.

I do not think you should create your own deco profiles for no deco dives.

I do a solid 15-20 feet safety stop (5 minutes or Adaptive) and on deep dives (greater than 80 feet) that approach NDL I may do a half maximum depth "pause" of one minute circumstances allowing.

My new computer is the Shearwater Peregrine. I think you need one.


James

 

[doctormike]

Hi, Barista…

Welcome to the tribe! Congratulations on your certification and your newfound love of scuba.

I’m not going to get into the science of staged decompression algorithms and gradient factors here because (1) I’m not qualified to do that, and (2) I think that it’s irrelevant to your situation. So to simplify things…

You said “deeper than 5m stops seem to reduce bubble and DCS risk in recreational dives (somewhat significantly).” I do not believe that is the case.

The incidence of DCS in recreation diving is very low, and of all of the efforts a new diver can make towards increasing safety, I think that there are better things to focus on than that, assuming that you stay within NDLs.

That having been said, there are things that you can do to make that very rare occurrence even less common. Some things to optimize are personal factors that are under your control (hydration, conditioning, etc…). And some things are dive related (computer settings, mix, depth and time). Of course, some personal factors are beyond your control (at least without surgery, like a PFO).

Your dive computer will let you stay pad the odds in your favor by simply changing the conservatism settings (don’t worry about GFs for that, just use the recreational adjustments). You can also simply not dive to NDL=0 and ascend sooner, making a dive plan with your team ahead of time to account for that.

The most efficient offgassing for a recreational diver happens with a DIRECT ascent to the surface at an acceptably slow rate. Any stops that you do on the way up simply delay that offgassing, and may actually result in increased nitrogen loading in at least some tissue compartments. The reason that they are done in technical diving is because there is enough inert gas loading that a direct ascent would result in unsafe overpressure in a compartment associated with an increased risk of bubble formation and clinical DCS. But by definition, if you are diving within NDLs, your N2 loading will not put you in that category, mathematically speaking.

The safety stop is not really recommended because of anything related to a decompression algorithm. Most agencies recommend it as a “speed bump”, to make divers (especially new divers) more aware of the ascent, to ascend with more care, and to avoid an overly rapid surfacing. This is particularly important in shallow water where the percentage change in pressure per foot is greatest.

So if you are really concerned about DCS, forget about staged ascents at this level, and plan your dive so that the risk dials are set where you feel comfortable.

Finally, you should know that the term "deep stops" can mean different things in different contexts. Much of the controversy about them, and the fact that they have really fallen out of favor in current thinking, relates to the term as a shorthand for "Pyle stops", whereas you may be using the term to refer to regular staged decompression stops. Again, beyond the scope of this discussion.

 

[lexvil]

You are WAY over thinking this.

 

[boulderjohn]

I do not agree with setting air and diving Nitrox. Instead just set your computer to a more conservative setting for the appropriate Nitrox mix you are using.

Correct.

Years ago someone got the idea of diving nitrox on an air setting, and the idea has taken on a life of its own. It's as if you only have two choices--air or nitrox. Why not dive nitrox 32 but use a nitrox 24 setting? O any other combination?

Don't lie to your computer. If you are using a computer that allows you to set gradient factors, just choose a gradient factor that keeps you far enough away from NDLS to be comfortable. A GF high of 70 is very conservative, and you can start there. (GF lows don't matter in NDL diving.)

 

[d^2b]

A GF high of 70 is very conservative, and you can start there. (GF lows don't matter in NDL diving.)

Yep, GF high of 75 is already more conservative than my Suunto Zoop Novo on the first dive.

 

[drk5036]

Yep, GF high of 75 is already more conservative than my Suunto Zoop Novo on the first dive.

Right. If you do set your computer to this level of conservatism, make sure you talk it over with your divemaster (if doing a guided dive) or dive buddy ahead of time. You could be decreasing your bottom time by a significant amount by being that conservative.

 

[tursiops]

Years ago someone got the idea of diving nitrox on an air setting, and the idea has taken on a life of its own. It's as if you only have two choices--air or nitrox.

This might have come about pre-common-computers when many were using tables for air or 32%; setting anything in-between required the complication of EAD tables and nobody did it.