Doubts about min deco ascents?

floater · October 9th, 2006, 05:22 PM

In DIRF I was taught to use the basic linear (3m/min) ascent from 80% ATA for rec dives (but with an emphasis on the 9/6/3m stops). The idea was that this would eliminate bubbles/nitrogen efficiently.

However, someone emailed me a study of 22 volunteer rec divers who did 181 actual dives total to 25m for 25min, followed by 3.5h SI and another dive to the same depth for 20min. The dives were done each weekend for 8 weeks with no other diving imbetween and the profiles were recorded to ensure accuracy. I presume they were using air. 8 different types of ascent profiles were tested; no stops, a shallow stop only (5 min), and both a shallow and a deep stop (5 min each), plus various ascents rates were used.

In terms of bubbling the linear (3m/min) ascent was the worst (albeit it started from depth). Still I'm having some doubts now about linear ascents, so I was wondering what others think about this study and also whether anyone knows whether GUE has done their own bubble testing of various rec profiles.

The study (PDF) is here: https://www.daneurope.org/eng/uhm%20...ep%20stops.pdf

I've attached pics of the tables that summarize the results.

GLOC · October 9th, 2006, 05:39 PM

That surprises me somewhat but a question I have, which doesn't seem that apparent from the study, is what gas were they using?

Using 32% gives 1 @9 and 1@6 using DP 20/85.
Using 21% gives 1@12, 1@9, 2@6.

I am also surprised that 5mins at 15m wouldn't add to the 'deco' time?

Using 21% there is no 12m stop, but 9m is 1m and 1m at 6m, 32% gives 1@6m.

I know that the profiles from DP are just one set of profiles.

fraser · October 9th, 2006, 06:16 PM

When did you do Fundies? Not sure if this has changed over time, but now (AFAIK) Min deco for a 25m/25mins dive would be 1@9, 1@6 and 1@3, not 3m a min all the way from 80% atas.

Cheers,

Fraser.

floater · October 9th, 2006, 06:23 PM

Quote: (Originally Posted by fraser)

When did you do Fundies? Not sure if this has changed over time, but now (AFAIK) Min deco for a 25m/25mins dive would be 1@9, 1@6 and 1@3, not 3m a min all the way from 80% atas.

Cheers,

Fraser.

I took DIRF January this year.

Do you include the ascent time in your 1 minute stops? If so it's basically a 3m/min ascent.

How fast were you taught to ascend to 9m from depth?

To be more exact, my instructor said you could include the ascent time in the stops or just do an actual 1 min stop at 9/6/3m, respectively, if you prefered.

floater · October 9th, 2006, 06:41 PM

Is it just me (or my computer) or does this thread not show up among new posts or recent threads?

GLOC · October 9th, 2006, 06:42 PM

Its 1@9, 1@6, 1@3 or as you say 3m/min from 9m upwards and gaining control of the ascent (9m/min) from 50% ATA for rec level dives.

Quote: (Originally Posted by floater)

Is it just me (or my computer) or does this thread not show up among new posts or recent threads?

It's you

limeyx · October 9th, 2006, 06:53 PM

Quote: (Originally Posted by floater)

I took DIRF January this year.

Do you include the ascent time in your 1 minute stops? If so it's basically a 3m/min ascent.

How fast were you taught to ascend to 9m from depth?

To be more exact, my instructor said you could include the ascent time in the stops or just do an actual 1 min stop at 9/6/3m, respectively, if you prefered.

I do both -- a 1 min stop *and* include ascent time in the stops.

I dont have a "seconds" hand so what I do is:

1) ascend at 30fpm to 50% of depth (for rec dives) ignoring the "pauses" pretty much
2) wait for my timer to tick over to the next minute (say it's on 30 when I hit the first stop -- wait for 31, or if that seems to come "too quick" then 32)
3) move to the next stop -- this ascent time is "included" in the next stop (so the ascent to the next stop is counted as though I am already there). When the timer hits 32 mins (or however many mins the stop is) then I move from that stop, even if I only just got there when the minute ticked over (or worse, am not even there yet)

this means that once you hit the first stop, you have a fixed amount of time to get out of the water -- no adding on time for sloppy slow ascent rates.

On dives 2+, we usually ascend 6 mins from 20 feet (1 min every 3 feet) if we've been going deep. if not, then just slow it down from 20 feet.

The pauses from 80% (we were told) are not "30 sec" pauses they are more like "did we lose anyone -- is everyone still here and responsive" pauses and to help you keep the ascent rate under control.

LCF · October 9th, 2006, 07:18 PM

I've discussed the Marroni study with a number of people, and the consensus has been that the issue with it is the 10 fpm ascent all the way from the bottom. If you do a 30 fpm ascent to 50% max depth, and then ten fpm above that, you basically end up doing the minimum deco 30, 20 and 10 foot stops. 80% of ATA starts your stops too deep for most recreational profiles.

rjack · October 9th, 2006, 07:51 PM

The Spencer scores were also done in a less than optimal way as I recall. I'm a bit fuzzy on the details (its been awhile) but they recorded a bubble score at a set time post dive rather than the max score experienced by any individual (regardless of whether it was 10 or xyz minutes post dive)

floater · October 9th, 2006, 08:09 PM

Quote: (Originally Posted by LCF)

I've discussed the Marroni study with a number of people, and the consensus has been that the issue with it is the 10 fpm ascent all the way from the bottom. If you do a 30 fpm ascent to 50% max depth, and then ten fpm above that, you basically end up doing the minimum deco 30, 20 and 10 foot stops. 80% of ATA starts your stops too deep for most recreational profiles.

I don't see the 10 fpm ascent as a big deal because if you add it to the bottom time, then it's still within the min deco rules. Namely here's part of the table that people seem to use (I was taught this too):

15m 60 min
18m 50 min
21m 35 min
24m 30 min
27m 25 min

So 25 or 20 minutes at 25m is clearly fine even if you add a few minutes to it for the slow initial ascent. i.e. Add 5 minutes to your bottom time and bump the average depth to 24m instead of 25m, then you are still within the table and you can consider the last 3m/min from 15m to be your min deco ascent. Granted you cannot use it to compare with the other profiles since you on-gas a few minutes longer, but you can say that it produces a butt load of bubbes (high or very high grade) in about 40% of the 22 subjects.

Also, would a few extra minutes at depth really make such a big diffrence to how much you bubble, or would the ascent itself be the likelier suspect?

Now the study may be flawed. The sample is small. Some people canceled dives because of cold or rough conditions which points to potential flaws and we don't know how healthy, fit and well-hydrated they were to begin with, but that's why I'm curious to know more about this and also what evidence GUE used to come up with the linear min deco ascent.

October 9th, 2006, 05:39 PM	#2 (permalink)
GLOC(Offline) Moderator Join Date: Nov 2005 Location: Fleet, Hants Posts: 1,950	That surprises me somewhat but a question I have, which doesn't seem that apparent from the study, is what gas were they using? Using 32% gives 1 @9 and 1@6 using DP 20/85. Using 21% gives 1@12, 1@9, 2@6. I am also surprised that 5mins at 15m wouldn't add to the 'deco' time? Using 21% there is no 12m stop, but 9m is 1m and 1m at 6m, 32% gives 1@6m. I know that the profiles from DP are just one set of profiles. __________________ Gareth Images of Life Photography DIR Team Foxturd Travels Underwater and Further Afar If you don't have the time to do something right, where are you going to find the time to fix it? - Stephen King Last edited by GLOC; October 9th, 2006 at 05:46 PM.

October 9th, 2006, 06:16 PM	#3 (permalink)
fraser(Offline) "I'm only late on your timescale" Join Date: Nov 2005 Location: Kent, UK Posts: 463	When did you do Fundies? Not sure if this has changed over time, but now (AFAIK) Min deco for a 25m/25mins dive would be 1@9, 1@6 and 1@3, not 3m a min all the way from 80% atas. Cheers, Fraser. __________________ Damn it feels good to be a gangsta

October 9th, 2006, 06:42 PM	#6 (permalink)
GLOC(Offline) Moderator Join Date: Nov 2005 Location: Fleet, Hants Posts: 1,950	Its 1@9, 1@6, 1@3 or as you say 3m/min from 9m upwards and gaining control of the ascent (9m/min) from 50% ATA for rec level dives. Quote: (Originally Posted by floater) Is it just me (or my computer) or does this thread not show up among new posts or recent threads? It's you __________________ Gareth Images of Life Photography DIR Team Foxturd Travels Underwater and Further Afar If you don't have the time to do something right, where are you going to find the time to fix it? - Stephen King

October 9th, 2006, 06:53 PM	#7 (permalink)
limeyx(Offline) New Member Join Date: Nov 2005 Location: Los Angeles, CA Posts: 707	Quote: (Originally Posted by floater) I took DIRF January this year. Do you include the ascent time in your 1 minute stops? If so it's basically a 3m/min ascent. How fast were you taught to ascend to 9m from depth? To be more exact, my instructor said you could include the ascent time in the stops or just do an actual 1 min stop at 9/6/3m, respectively, if you prefered. I do both -- a 1 min stop and include ascent time in the stops. I dont have a "seconds" hand so what I do is: 1) ascend at 30fpm to 50% of depth (for rec dives) ignoring the "pauses" pretty much 2) wait for my timer to tick over to the next minute (say it's on 30 when I hit the first stop -- wait for 31, or if that seems to come "too quick" then 32) 3) move to the next stop -- this ascent time is "included" in the next stop (so the ascent to the next stop is counted as though I am already there). When the timer hits 32 mins (or however many mins the stop is) then I move from that stop, even if I only just got there when the minute ticked over (or worse, am not even there yet) this means that once you hit the first stop, you have a fixed amount of time to get out of the water -- no adding on time for sloppy slow ascent rates. On dives 2+, we usually ascend 6 mins from 20 feet (1 min every 3 feet) if we've been going deep. if not, then just slow it down from 20 feet. The pauses from 80% (we were told) are not "30 sec" pauses they are more like "did we lose anyone -- is everyone still here and responsive" pauses and to help you keep the ascent rate under control. __________________ my divelog: http://www.mydivinglife.com/limeyx

October 9th, 2006, 06:23 PM	#4 (permalink)
floater(Offline) Mostly harmless Join Date: Nov 2005 Location: Currently in the US, but I'm not American Posts: 155	Quote: (Originally Posted by fraser) When did you do Fundies? Not sure if this has changed over time, but now (AFAIK) Min deco for a 25m/25mins dive would be 1@9, 1@6 and 1@3, not 3m a min all the way from 80% atas. Cheers, Fraser. I took DIRF January this year. Do you include the ascent time in your 1 minute stops? If so it's basically a 3m/min ascent. How fast were you taught to ascend to 9m from depth? To be more exact, my instructor said you could include the ascent time in the stops or just do an actual 1 min stop at 9/6/3m, respectively, if you prefered.

October 9th, 2006, 06:41 PM	#5 (permalink)
floater(Offline) Mostly harmless Join Date: Nov 2005 Location: Currently in the US, but I'm not American Posts: 155	Is it just me (or my computer) or does this thread not show up among new posts or recent threads?

October 9th, 2006, 07:18 PM	#8 (permalink)
LCF(Offline) New Member Join Date: Dec 2005 Location: Seattle Posts: 622	I've discussed the Marroni study with a number of people, and the consensus has been that the issue with it is the 10 fpm ascent all the way from the bottom. If you do a 30 fpm ascent to 50% max depth, and then ten fpm above that, you basically end up doing the minimum deco 30, 20 and 10 foot stops. 80% of ATA starts your stops too deep for most recreational profiles.

October 9th, 2006, 07:51 PM	#9 (permalink)
rjack(Offline) wet behind the ears Join Date: Nov 2005 Location: Seattle, WA Posts: 860	The Spencer scores were also done in a less than optimal way as I recall. I'm a bit fuzzy on the details (its been awhile) but they recorded a bubble score at a set time post dive rather than the max score experienced by any individual (regardless of whether it was 10 or xyz minutes post dive)

October 9th, 2006, 08:09 PM	#10 (permalink)
floater(Offline) Mostly harmless Join Date: Nov 2005 Location: Currently in the US, but I'm not American Posts: 155	Quote: (Originally Posted by LCF) I've discussed the Marroni study with a number of people, and the consensus has been that the issue with it is the 10 fpm ascent all the way from the bottom. If you do a 30 fpm ascent to 50% max depth, and then ten fpm above that, you basically end up doing the minimum deco 30, 20 and 10 foot stops. 80% of ATA starts your stops too deep for most recreational profiles. I don't see the 10 fpm ascent as a big deal because if you add it to the bottom time, then it's still within the min deco rules. Namely here's part of the table that people seem to use (I was taught this too): 15m 60 min 18m 50 min 21m 35 min 24m 30 min 27m 25 min So 25 or 20 minutes at 25m is clearly fine even if you add a few minutes to it for the slow initial ascent. i.e. Add 5 minutes to your bottom time and bump the average depth to 24m instead of 25m, then you are still within the table and you can consider the last 3m/min from 15m to be your min deco ascent. Granted you cannot use it to compare with the other profiles since you on-gas a few minutes longer, but you can say that it produces a butt load of bubbes (high or very high grade) in about 40% of the 22 subjects. Also, would a few extra minutes at depth really make such a big diffrence to how much you bubble, or would the ascent itself be the likelier suspect? Now the study may be flawed. The sample is small. Some people canceled dives because of cold or rough conditions which points to potential flaws and we don't know how healthy, fit and well-hydrated they were to begin with, but that's why I'm curious to know more about this and also what evidence GUE used to come up with the linear min deco ascent.