PerroneFord changed my thinking, n maybe even saved my life.

[PerroneFord]

All dives are decompression dives...

You've been doing mandatory decompression dives all along. You were just doing the mandatory stop on the surface instead of in the water. I prefer to do mine in the water.

But now that you're actually THINKING about what you're doing, and what you have been doing, you are starting to understand why technical divers take so much more gas to breathe, and why they do those stops even on lesser dives than you've been doing.

So here's a question for you. Assume for a moment that you were diving your new way, and wanted to do the microbubble stops. And assume that just as you were about to begin your ascent, your buddy came to you and signaled OOA. With what you had left in your tank, could you have safely gotten your buddy and yourself to the surface? Or would you have had to break your new "safer" dive plan to get you home before you ran out of air? And if you would not have had enough, how could you dive in the future to make SURE you had enough for this kind of emergency? And yes, I know you have a 19cuft pony. Factor that in if you want.

 

[ronbeau]

We've been doing 'Half the deepest depth' stops for atleast a full minute (ie 120 deep, stop at 60 for a minute) then complete a normal 3 minute stop at 15-20ft. Alot of doc's have said that half stops show significant improvement in off gassing.

For just me personally, the more work or swimming I do hunting for bugs at 85ft, the better I feel after a dive. I don't know if the increased effort and subseqent blood flow helps in the efficiency of off gassing bubbles, but seems to work.

Since we drift, I usually shoot my SMB at 30 ft and then crawl slowly to the surface as I wrap up the line.

Thanks for posting some good info for readers here!!

Actually this has been changed in a recent (second quarter 2008) standards & procedures update issued by NAUI to all of its instructors. The text of that notification appears below.

Rule of Halves Revised

Based upon the most current research and
analysis of decompression science on the
value of deep stops in “no-required-decompression”
diving by Bennett et al (​

​

​

​

Undersea
and Hyperbaric Medicine 2007; 34(6):
399-406, the NAUI Board of Directors
approved a change to the NAUI Standards
and Policies on March 7, 2008, at its annual
meeting. A reprint of the study is included
in this issue of Sources (pp. 48 ff).

The membership is advised to make a pen
and ink change in their personal copy of
the manual and mark both the title page
and changed page with “rev. 1-08.” Notice
of these changes is included in existing
inventory of the NAUI Standards and
Policies Manual, and the changes will be​

incorporated in the next printing.

S&P Page 2.16 – Current wording​

It is recommended that following dives in
excess of 40 feet (12m), divers make a ​

​

​

​

one
minute stop at a depth that is half that of
the deepest depth reached during the dive
and make a precautionary stop in the
10-20 feet (3-6m) zone for three to five
minutes before returning to the surface.
The precautionary stop time may be
considered “neutral” time- not counted as
either dive time or surface interval time.​

S&P Page 2.16 – Changed wording​

It is recommended that following dives in
excess of 40 feet (12m), divers make ​

​

​

​

a two
to three minute stop (with two and​

one-half minutes being optimum) at a

depth that is half that ​

​

​

​

of the deepest depth
reached during the dive and make a
precautionary stop in the 10-20 feet (3-6m)
zone for one minute before returning to
the surface. The precautionary stop time
may be considered “neutral” time- not
counted as either dive time or surface
interval time.
Bennett et al have extended their study
to include diving over a greater range of
depths from deep (130 fsw) to shallow and
will present these findings at the UHMS
“Decompression and Deep Stop Workshop”
on June 24-25, 2008, in Salt Lake City,
Utah, sponsored by NAUI Worldwide and​

other dive industry members.

 

[mos11b1p]

Well, Perrone. Let’s see if I paid attention in Nitrox class. Gonna try and figure this one out on my own. I don’t have software. Im not a deco diver. I am just gonna wing this from my head. Gonna do some “rounding” as we go along. You’ll be able to see where I take that liberty. Here goes:

My breathing rate is: .903 cf/min at work @ 1 bar
.516 cf/min at rest. @ 1 bar

Split the dif: .710 cf/min @ 1 bar

The microbubble stop profile indicated:
30ft for 1min (call it 33ft ) =.710cf/min*1min*2bar = (total: 1.419cf)
20 ft for 3min = .710cf/min*3min*1.66bar = 3.536cf (total: 4.955cf)
10 ft for 6min = .710cf/min*6min*1.33bar = 5.666cf (total: 10.621cf)

So I need approx 10.621cf of air to do my microbubble stops.

Getting up from 132ft to 30ft? Don’t know how to calculate this…. Hm. I’ll just take a guess.

132ft ascent rate is approx 58ft/min…so 132ft to 103ft is .5min.

.710cf/min*.5min*5bar = 1.775cf

103ft ascent rate is approx 43ft/min. 103ft to 81ft is .5min
.710cf/min*.5min*4bar = 1.42cf

81ft ascent rate is approx 34ft/min. 81ft to 64ft is .5min
.710cf/min*.5min*3.5bar= 1.243cf

64ft ascent rate is approx 30ft/min. 64ft to 49ft is .5min
.710cf/min*.5min*3bar= 1.065cf

49ft ascent rate is approx 27ft/min. 49ft to 35ft is .5min
.710cf/min*.5min*2bar= .71cf

Let’s just say I got to 30 feet already! LoL
1.775cf + 1.42cf + 1.243cf + 1.065cf + .71cf = 6.213cf of air to get to 30ft

6.213cf of ASCENT air + 10.621cf of STOP air = 16.83cf of air to get out of the pool.

I need 16.83cf. My OOA emergency buddy is in panic…so he needs TWICE that. so add another 33.66cf. TOGETHER we need 50.49cf of air to make it out with microbubble stops. Now I started my ascent with a 1000 pounds of air (to make sure I make it back to the boat with 500psi). That’s 1/3 of a 3000psi AL80. An AL80 holds 77.4 cf of air at 3000psi. 1/3 of that remains…25.8cf. I am carrying a 19cf pony bottle that is topped off. So we’ve got 44.80cf of air to work with…. My calculations say 50.49cf is a WORST case scenario. There is no doubt we will calm down by the time we reach our microbubble stops and MAKE UP that missing 5pounds of air…so I would say that YES… in a OOA emergency at 132ft…at the very end of the dive, just before beginning ascent… I could get my buddy to the surface with microbubble stops for both of us. We would arrive to the surface with little or no air…but we’d make it. However… now I know why my dive mentor carries a 40cf for a pony!!! lol (side note... the pony has only one reg. So I would need to switch to it right of the bat and burn it. It is MORE than enough for me to get top side. All the 1000pounds of remaining air in my AL80 goes to my buddy. If He calms himself down... he should have no problem making it on my remaining air...the air I intended to use in the FIRST place to get back to the boat with 500pounds still left.)

 

[PerroneFord]

That's very good. The microbubble stops are good, but probably not necessary in a true emergency. So you could probably miss one or two of them and still be fine. However, this exercise should show how close some people come to disaster without even realizing it. You carry a pony and begin your ascent with 1000psi. How many diver do we know that don't have any redundant air, and would look at you like you're silly for leaving the bottom with 1000psi.

In terms of technical diving, we double our normal SAC rate and use that as our factor for escaping a bad scenario. So in your case, we'd double your .71 for an emergency rate and double our buddies as well, and work the math. It doesn't take much to see that with a common AL80, we wouldn't get much dive time at all if we truly planned to do a safe ascent. Especially if we had been below 100ft.

So last question for you. I understand your mentor has a 40cuft pony. What about the rest of your dive buddies. If YOU were the one who had a catastrophic gas failure, would they be able to get you home? Do they also begin their ascent with 1000psi? If they do, then awesome. If not, you may want to find out what they actually do, and plan accordingly.

Glad to hear your having fun out there. And nice to see someone trying to do this stuff safely.

 

[Johnoly]

It is recommended that following dives in
excess of 40 feet (12m), divers make
a two to three minute stop (with two and
one-half minutes being optimum) at a
depth that is half that
of the deepest depth

Now that is excellent updated information for us, Thank you!!!

 

[S&V]

Good discussion by all, thanks!

 

[ucfdiver]

DIR-diver.com - Using the min deco table

I really think every diver should read that page.

 

[Diveral]

A truly excellent discussion.

Thank You

 

[Blackwood]

Ok question about the "half stop." We all know that below 20 feet...we are loading nitrogen. Had I stayed DOWN at 120 for a while at that depth...I might have such staturation levels in my blood...that hovering at 60 feet would actually be releasing some amount of nitrogen (hence the usefullness of a 60foot stop on a 120 dive)...but depending on the profile...had I not spent much time "at depth", then i might just as well be LOADING nitrogen during that "1 minute half stop." Correct?

There is no cut and dry answer.

Not all parts of your body on/offgas at the same rate. Note that I bolded the word blood in your post. It's generally accepted that blood is among the fastest tissues in the body. At any given depth there is an ambient pressure, and that corresponds to the saturation pressure (highest pressure that will eventually be reached in the tissues without further increasing the ambient, i.e. descending). Many decompression models assign blood a halflife of 5 minutes. That means that, at any given depth, your blood will more or less stop ongassing after about 25 minutes (when it's reached 97% capacity). That's true at the surface, at 20 feet, and at 200 feet. The difference between those levels is the pressure to which the tissue saturates.

Those tissues which have ongassed enough to raise their internal inert gas pressures to greater than the ambient pressure at the level to which you ascend will offgas. Those tissues which are substantially slower (bone, fat, cartilage, etc.) may still be ongassing.

The question is: do you care? As a diver, your main concern from a decompression standpoint should be Type II DCS, or DCS that attacks your central nervous system. Theoretically, it's bubbles in the fast tissues that cause Type II DCS.

 

[doole]

Still I have returned to the boat at least ONE time, and begun to feel very “strange” on the surface. I could not put my finger on it but something wasn’t right inside me AT ALL. To be honest…it was scary.

To me, this brings up an interesting point that nobody talks about much: we are taught at the very beginning that it's also possible to get bent "undeservedly"; i.e. while diving within the tables, simply because of the nature of the decompression model and the fact that it IS a model.

I think that you can learn to actually feel when you need more deco time than tables / devices recommend. There are at times all kinds of little weird symtoms towards the end of a dive in my experience, and I have felt much better at the surface since I started paying more attention to them - things I might previously have dismissed as not worth paying attention to. A very slight tickle in the end of my little finger, as a random example, might cause me to tack on an extra minute at the current depth.

It's a bit hard to talk about simply because you obviously don't want people starting to try to "feel" when decompression stops are required, but as long as the normal theoretical obligations are met, I think it's a good idea to try this over and above normal obligations. Just a thought, because it has worked very well for me.

Of course, the fact that I was born when the earth was still cooling factors heavily into my deco requirements as well.

Yes, great thread.