Questions about the 3 min safety stop....

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DC53

DC53

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Location
Naples, Florida
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200 - 499
My question regards the three minute stop at 15 feet in the setting of recreational, no decompression diving... Yesterday my wife and I did a 40 minute dive. Most of it was in the shallow zone of the quarry at around 30-35 feet, working on skills, doing the swim throughs, etc., and then we made one short descent to around 70 feet. I.e., we were very much within the safe no decompression limits. Later my wife asks me, “If we were so much inside of the safe no decompression limits, why did we have to do the 3 minute safety stop?” (Now let me say that neither of us is in any way against hanging out at 15-18 feet for 3 minutes!) However, I could not give a concrete answer and so I am asking for input.

I have a related question which may be answered by responses to my question above. As you get near to decompression limits but still within the no-deco range (ie lots of nitrogen bubbles on the computer but no solid dots or deco warnings, or, going by the table but closer to the limits), does the safety stop serve as precautionary but non mandatory decompression stop?
 
"...the safety stop serve as precautionary but non mandatory decompression stop"

Well stated. That's a very concise and accurate description, and should answer your wife's question.

Other members will likely come and tell you the history of why They started recommending stops (had to do with people ascending much faster than the rates upon which the NDLs were computed).
 
Many - myself included - will tell you that ALL dives are decompression dives. Within recreational "No Deco Limits" conventional wisdom is that the stop is not MANDATORY, but that doesn't mean you wouldn't benefit from doing it.
 
RJP:
Many - myself included - will tell you that ALL dives are decompression dives. Within recreational "No Deco Limits" conventional wisdom is that the stop is not MANDATORY, but that doesn't mean you wouldn't benefit from doing it.
Click to expand...

All dives are decompression dives, but not all dives require decompression stops because the time spent ascending (e.g. 1 minute from 60 feet on a 60fpm model) is sufficient to offgas to a safe surfacing ratio.

That's what an NDL is: the (time at depth) limit to which making a direct ascent to the surface (1ATM) at some prescribed maximum rate will provide sufficient decompression (e.g. <2:1 dissolved to ambient air pressure ratio or whatever the model says for each tissue 'compartment').
 
DC53, you did very well at answering your own question. Even though safety stops are just that, "safety stops" as opposed to mandatory decompression stops, it's good to get in the habit of doing them at the end of every dive, no matter how much time your computer says you have left before mandatory decompression. You and your wife appear to be very conscientious divers (based on your mentioning the practicing of skills). Look upon your safety stops as another way to practice your bouyancy skills and trim for three minutes after each dive.
 
Blackwood:
(e.g. 1 minute from 60 feet on a 60fpm model) is sufficient to offgas to a safe surfacing ratio.
Click to expand...

This "Golden Rule" was pulled out of thin air by the founding gods of recreational diving. It was born around a table littered with beer bottles and late night after-dive yacking.

Absolute fact... but not science.
 
DC53 - I think you should be complimented on your safety stop and you did quite a good job at answering your own question! I agree that safety stops can only benefit you. On deeper dives, I have been known to do an additional stop at 1/2 way for a couple of minutes even though I did not exceed my NDL. (Depends on what kind of diving I was doing). Also, I'm a firm believer in staying at my safety stop until I'm in the green even though I've completed the three minutes. (MY computer shoes green, yellow, red in bars) I know it's being over cautious, but if the thermocline is cooperating it can be fun depending on what kinds of games you can come up with. (Thermocline is at 20 feet now!!! YEAH!!!!!). Hope you continue to enjoy and have fun with diving!
 
Recently I have found that spending 3-4 more extra minutes for decompression (adding a deep stop, slowing down my ascent rate, etc.) has decreased my fatigue after the dive. Especially if we do 2 or 3 dives a day. You do not have to do it but it's better to. As it has been pointed out every dive is decompression dive and nitrogen load is an analog function , not digital (yes or no) the more you offgas the better. Stops help to accomplish this.
 
Around here a table littered with beer bottles and late night yacking always ends with "we should do that".... The next day always brings "who thought of this"!!! Seemed like a good idea at the time....
 
DC53:
My question regards the three minute stop at 15 feet in the setting of recreational, no decompression diving... Yesterday my wife and I did a 40 minute dive. Most of it was in the shallow zone of the quarry at around 30-35 feet, working on skills, doing the swim throughs, etc., and then we made one short descent to around 70 feet. I.e., we were very much within the safe no decompression limits. Later my wife asks me, “If we were so much inside of the safe no decompression limits, why did we have to do the 3 minute safety stop?” (Now let me say that neither of us is in any way against hanging out at 15-18 feet for 3 minutes!) However, I could not give a concrete answer and so I am asking for input.

I have a related question which may be answered by responses to my question above. As you get near to decompression limits but still within the no-deco range (ie lots of nitrogen bubbles on the computer but no solid dots or deco warnings, or, going by the table but closer to the limits), does the safety stop serve as precautionary but non mandatory decompression stop?
Click to expand...

Did you plan the dive on the tables? Assuming you're PADI, the RDP is quite clear about when a safety stop is *required* and when it's *optional*.

Personally I think you should always do a safety stop unless there is a very compelling reason to skip it. A safety stop will never increase your risk of getting DCS but skipping it might in some cases.

R..
 
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