Safe Ascent

[DCBC]

It's an interesting paper, but I wonder where they come up with the idea that it is KNOWN that the spinal cord has a 12.5 minute halftime?

I think that DAN took this from the book "Diving and Sub-Aquatic Medicine," by Edmonds, Lowry and Pennefather (I think it was published in the early 90's). I find it interesting that the spinal cord has the same 12.5 minute halftime for both Nitrogen and Helium where other tissues diffuse Nitrogen at a much slower rate.

 

[rjack321]

This DAN article might be interesting:

DAN Divers Alert Network

Try the original papers, much better.
2004 paper
Rubicon Research Repository: Item 123456789/1520

2007 paper updating the work and describing how just taking 1 min of a 3min safety stop and moving it deeper (to 50fsw) is inadequate.
Rubicon Research Repository: Item 123456789/7901

Personally, I really start slowing the ascent at about 50% of the depth for recreational dives or about 1.8atas up from the bottom for deco dives.

 

[boulderjohn]

2007 paper updating the work and describing how just taking 1 min of a 3min safety stop and moving it deeper (to 50fsw) is inadequate.
Rubicon Research Repository: Item 123456789/7901

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The 2007 paper is quite interesting. I was especially interesting in the poor results for one minute stops.

It seems to me that all the papers studied indicate a preference for a relatively fast ascent with more extensive stops at a prescribed depths rather than a very slow ascent. It would seem to me that a slow ascent with 1 minute stops would be pretty similar to a very slow ascent without stops, which they did not see as being as good. This would appear to me to be especially true of protocols that call for a series of one minute stops that include the travel time between stops as a part of the stop time.

 

[TSandM]

As I recall Marroni's work, though, they used the same ascent rate throughout -- in other words, if they did a 75 foot dive, they did a 10 fpm ascent from 75 feet. I wasn't all that surprised that that slow an ascent rate wasn't optimal from that depth.

The math strongly suggests that ascent rates ought to change as one gets shallower.

 

[boulderjohn]

The math strongly suggests that ascent rates ought to change as one gets shallower.

I agree.

 

[AfterDark]

I always used 60fpm or no faster than my smallest bubbles.

 

[gcbryan]

I think that 1 minute stops are less about the stop and more about making sure you slowed the ascent down.

A 1 minute stop for a deep stop isn't really enough time for any significant offgassing to occur even for the faster compartments.

Slowing the ascent down until you are well shallow of the controlling tissue offgassing point does nothing regarding offgassing.

I don't think these limited studies really showed much one way or the other.

 

[AfterDark]

I think that 1 minute stops are less about the stop and more about making sure you slowed the ascent down.

A 1 minute stop for a deep stop isn't really enough time for any significant offgassing to occur even for the faster compartments.

Slowing the ascent down until you are well shallow of the controlling tissue offgassing point does nothing regarding offgassing.

I don't think these limited studies really showed much one way or the other.

I've always added time onto the last stop on decom dives. A few minutes more at 10' isn't going to do any harm and could be difference from wondering what that rash is from?

 

[Blackwood]

I think that 1 minute stops are less about the stop and more about making sure you slowed the ascent down.

Exactly. It makes monitoring and controlling ascent rates easier.

Most of us can count to 10 seconds fairly accurately, but much beyond that we get off beat. (Other of us have seconds on our timing device).

So take the paradigm Lynne suggested: 30fpm to half your Dmax, and 10fpm to the surface.

On a dive from 100 feet, that would mean that every 10 seconds, you move 5 feet until you hit 50FSW.

1...2...3...4...5...6...7...8...9...0

Easy to count, easy to keep track.

Once you make it to 50, you can keep MOVING at the same rate, but add stops which will average out the shallow portion of your ascent to 10fpm. In the above case, move 30fpm (or 5f/10s), and stop for 40 seconds. Lather, rinse, repeat, surface.

 

[Karel26]

I just use my dive watch and then i keep looking up to keep up with my bubbles so that i know if my watch die then i can still ascent with out it. .