Ascent Rate (SSI vs PADI)

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nv

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Location
Miami
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My gf is getting certified through PADI and I looked over the Open Water Diver Manual and compared some of the teachings to SSI, the agency that I was certified with.

To my surprise, the PADI course is much more laid-back and less conservative in comparison to SSI. For example, the PADI manual rate of ascent is double SSI or 60ft/min. SSI is 30/min.

Furthermore, many computers, to my knowledge, would consider 60ft/min a fast ascent and will probably lock you out of further dives.

Thoughts...

Thanks


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---------- Post added April 21st, 2014 at 10:27 PM ----------

There are other differences where SSI is more conservative and/or requires you to learn more, but this is the one that caught me by surprise.


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---------- Post added April 21st, 2014 at 10:32 PM ----------

saga6ete.jpg



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My computer is ok with 60 fpm below 60' but has been training me to slow to below 30 fpm above 60', as well as doing a safety stop @ 15'. It does not lock me out for ignoring either or both. Prior to the computer I was doing 60 fpm or less with no safety stop since 1963 per the US Navy Dive Manual which was the authority on diving.



Bob
-------------------------
I may be old, but I'm not dead yet.
 
To my knowledge no computer will lock you out, it may however penalize you (suunto) on future NDL times for following dives.
 
Whether it be a lock out or some kind of penalization, the 60ft/min seems to be a lot faster than the computers I use recommend/coded with.

Puck and Veo

What comps are you guys using?


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I believe my average ascent rate is considerably slower than PADI's 60'/minute but probably not as slow as 30'. My Mares 2 computer is OK with that. I don't know if other agencies were aligned with the 60' when that came out or not. But I believe it was just an arbitrary figure, being close to a midway point between 25' and 100' per minute (2 different organizations, 1 being the US Navy I believe, used these speeds). Then I believe in later years more were recommending the 30', and PADI said 60' is the absolute fastest you should go--slower being better. I don't think it's too crucial which is exactly right, as I don't THINK there is much, if any, scientific proof either way. What everyone seems to take from all this is slower is better. As well, some argue in favour of deep safety stops and others say it doesn't matter. There is also discussion on if it is harmful re ongassing/offgassing if you ascend too slowly...
 
To my knowledge no computer will lock you out, it may however penalize you (suunto) on future NDL times for following dives.

The Mares Puck will lock out the diver after a too-fast ascent (and go into gauge mode). It does so when the diver exceeds the maximum rate for a stretch equal to at least two-thirds of the depth at which the audible alarm was triggered. The maximum rate is 39 fpm. The manual mentions an option to disable this "feature."

The Suunto Zoop (and presumably many other Suunto models) will add a mandatory safety stop if you exceed the designated maximum ascent rate, which for the Zoop is 40 fpm momentarily or more than 30 fpm continuously.
 
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The reason for the differing ascent rates between agencies comes down the differences in the tables they use for dive planning. The SSI tables are based much more closely to the original US navy tables (although they have been adapted from their original form) - whereas the PADI tables have been further developed in conjunction with DSAT (Dive Science & Technology).

The US Navy/SSI use the 120 minute wash in/out rate as their control group for gas absorption & release - so if you look at the SSI tables the max surface interval is 12 hours. This model assumes it takes longer for your tissues to fill with nitrogen during a dive, but also longer for it to wash out afterwards. The PADI RDP uses a 60 minute wash in/out rate as their control group for gas absorption & release - so if you look at the RDP tables the max surface interval is only 6 hours. This model assumes it takes less time for your tissues to fill with nitrogen during a dive, but also less time for it to wash out afterwards. So the truth is that both tables are conservative in their own way. These controlling wash out rates the different agencies use are also the reason for the differing ascent rate recommendations - SSI max asc rate is 9metres per minute and PADI is 18metres per minute (sorry, don't do feet!).

When it comes down to it however, it doesn't make a huge difference which you use, as long as you follow the rules and remain within your NDL's of whichever table you are using - and do not transfer pressure groups between different agency tables. Dive computers all work off their own algorithm anyway, most of which are all different to both the SSI & PADI tables. I personally use a Suunto computer (which uses the RGBML algorithm - don't ask me what that stands for, I don't have a clue!), which beeps lie crazy if you hit 12m per minute. I teach both PADI and SSI, and as I always say to my students when explaining these differences, nomatter what the recommended ascent rate is, this is the limit, not a target - slower is always better. I personally ascend at around 6-8metres per minute max, but normally even slower.
 
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I'm with Bob on this. For years I would boogie from deep water and hit the brakes at 60' or so and wander to the surface without a safety stop. I started doing stops when charters required them. Now when diving from my boat, I still hang out for a bit at 15'. Seems prudent since I'm no longer the vibrant youth I once was. I also solo dive much of the time and don't push any buttons I don't have to. My Galileo Sol will harp at me doing fast ascents, but won't lock out. It uses a variable ascent rate between 23-65 ft/min based on exposure. I just follow its' guidance, including any deep or decompression stops. most of the time it is spot on with the pre-dive plan. I think what throws it off is the workload measurement based on rate of consumption. High CO2 can bust you up on ascent too.
 
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PADI will win! :D

You can read a brief history of ascent rates as TMHeimer described on the US Navy Experimental Diving Unit's website here:

The United States Navy Experimental Diving Unit: ** Diving History -- John Scott Haldane "Father of Modern Decompression"....and a bunch of other stuff **

Says it started at 25ft, then 60ft, now back to 30ft/minute (just read the ascent rate section)




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---------- Post added April 22nd, 2014 at 07:20 AM ----------

At the end of the day I'm going to stay to what I learned and follow my computers as they are pretty close to my tables.


But I do think is 60/ft/minute is fast.


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---------- Post added April 22nd, 2014 at 07:21 AM ----------

At the end of the day I'm going to stay to what I learned and follow my computers as they are pretty close to my tables.


But I do think is 60/ft/minute is fast.


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