Hi Wolfie, (nice name, BTW)
Here is the deal on safety stops. There is nothing magic about 3 minutes. Those countdown timers on recreational computers are dumb, because they imply a level of accuracy in the deco algorithms that just isn't there.
Q: If your buddy drops his mask overbaord, and you pop down to 40' to get it. Should you do a safety stop, even if you were only down for 30 seconds? YES!
There are 2 reasons to do a safety stop. First and most important is to fully arrest your ascent in the middle of the final doubling in volume of all the air spaces in your body. Always do this! Skipping the deco stop entirely on a 'simple errand' like that is a great way to give yourself an AGE.
The second is to consider your situation, including the risks of getting bent and to make a conscious decision to surface when the time is right. In the case of the dropped mask, that might just be verifying your N2 loading is negligible and looking up to avoid hitting your head on the boat before going up. The whole thing could be done in under 5 seconds, but you should still do it.
At the other extreme, if I'm at the end of my second air dive, 12 miles off the coast of ecuador, and I know even the most primative medical help is at least an hour away, I might hang out at the safety stop for 5 or even 10 minutes beyond any manitory deco stop. If I have the air and I'm not cold or being pulled away by current, it's the prudent thing to do.
For computers that are used for deco diving, that countdown timer is a hazard, because it could be confused with a manditory stop. (or worse, a manditory stop might be mistaken for the silly deco stop timer and ignored)
To sumarize, there is nothing magic about 3 minutes on a safety stop. The main thing is that you 1: STOP and 2:THINK before you surface on every dive.
The thinking will tell you how long to stay there. The things to consider include: remaining air, current, N2 loading, in water hazards (fishing gear, boats, jelly fish, etc), manners (If I'm the last one down and they are waiting to pull anchor, I dont want to delay everyone) and physiology. (If I'm cold or about to pee in my drysuit, I'll come up sooner
You don't want the computer to try to do the thinking for you. It's just there to run a deco algorithm. (you wouldn't ask the speedometer in your car to tell you how fast to drive, would you?) A prudent driving speed is a similarly complex trade off of many safety and practical considerations.
