Can someone explain Ratio Decompression?

[limeyx]

Every time I see this thread and its title "Can Someone Explain Ratio Decompression" I can't help but think the only possible post is:

No.

...I could but I might give you DCS heh heh heh

seriously, it'd been rehashed so much that a search would be better than doing it all over again yet again

 

[Kevrumbo]

An AL40 does last about 30 minutes of deco as a 70 bottle, but there is more to it.Minimum stop times are applied to the various depths from 0 - 30, 31 -60, 61 - 90, 91 - 120, and 121 - 150 minutes of deco at the O2 Segment. Using Cascade Deco, you determine how much deco you need on O2 at 20' and then figure out the rest of the deco based on that. From there, depending on how long the deco segment is, determines the minimum time for each stop and even how you curve the deco. Your Cascade Deco document, while mostly accurate, leaves out a lot of information. You can also use it for dives shallower than 150'.

For example. On at 400' dive for 150 minutes, you wouldn't do 2 minute stops at each deco stop and then finish off the deco segment with the remaining time. Nor would your deep stops be one minute long. Your total run time is going to be about 10 hours after you take into account for ascent to deep stops, the deep stops, the deco at the four different deco segments, and a six minute ascent from 20.

I think you're now referring to the Deep Stop Table:

	NDL​	30​	60​	90​	120​	150​
75%​		1​	2​	3​	4​	5​
50%​	1​	3​	5​	7​	9​	10​
35%​	3​	7​	11​	15​	19​	20​

To clarify, the deep stop table is apart from and has nothing to do with "the minimum stop times applied . . .of the O2 segment".

From AG's Ratio Deco Class (that I took almost six years ago:shocked2: !), simply stated: Your NDL for any depth greater than 130'/39m is 5min. Anything over that, apply the WKPP Deep Stop Table above and the rules for calculating your O2 & deco gas segments as described above in Cascading Ratio Deco. . .

For your extreme example of 150 minutes Bottom Time at 400':
Your first deep stop is at 75% of 400' which is 300': the table gives 5min and for every 10' up from 300' thereafter;
Second deep stop is 50% of 400' which is 200': the table now shows 10min etc;
Third deep stop (if you haven't already switched to an intermediate trimix deco gas yet),
35% of 400' which is 140': the table shows 20min etc. until you reach a deco gas switch segment. . .