On my last dive, after a pretty moderate NDL exposure of 45min at an avg depth of 17m (~55ft) I started a slow ascent with my two buddies. One buddy lost a double ender on the ascent at around 5m (~16ft). I saw it dropping and land on the sand bottom at 10-11m (30-35ft). I quickly popped down to get it for him since he had an SMB up, and ascended again to rejoin my buddies at 5m to continue our slow ascent to the surface.
As far as I know, such a small bounce after a moderate N2 loading shouldn't pose any problems, especially not with a final slow ascent, but it did make me think about how much the variables of exposure and depth of bounce would need to change before it starts becoming problematic.
Another example:
5 divers split into two groups descend to do a dive together. Me and my buddy descended together down to 15m (~49ft). We stabilize and start approaching the other group that turns out to be a complete mess. One diver is popping to the surface, the other two are stirring up the silt swimming back and forth along the bottom and flashlights are swinging everywhere. We abort the dive, I do a slow ascent with my buddy and rejoin the other divers on the surface at around 15 minutes of elapsed total dive time. I agree with my buddy for us to do a dive without the other group, and we descend to 30m and have a nice 40 minute dive crawling up along a wall.
Again, with the minimal N2 loading of maybe 10 minutes at a maximum of 15m, I don't think there's a problem with restarting the dive without a surface interval.
My questions are:
1 - am I wrong in my assessment? Are any of these examples considered risky?
2 - it is my understanding that the major issue with descending after an ascent, is the possibility of gas bubbles being recompressed and passing over into the arterial blood flow, and that this is an important reason for the mandatory surface interval - is this correct? Are there other considerations?*
3 - Where do you draw the line?
A) In the first case: what are the limits of exposure and bounce you would be comfortable with?*
B) In the second case: how much of an exposure would you say warrants a mandatory surface interval?
4 - Or am I completely overthinking this out of proportion, surface intervals are not necessary when diving with a computer on NDL dives and bounces are not a problem?
*I expect that for deco dives this will be more problematic both in terms of available gas (if you were to redo any deco stops) and also in terms of higher load and more chance of bubbles - ie. dive your plan, if you drop something, let it go...
As far as I know, such a small bounce after a moderate N2 loading shouldn't pose any problems, especially not with a final slow ascent, but it did make me think about how much the variables of exposure and depth of bounce would need to change before it starts becoming problematic.
Another example:
5 divers split into two groups descend to do a dive together. Me and my buddy descended together down to 15m (~49ft). We stabilize and start approaching the other group that turns out to be a complete mess. One diver is popping to the surface, the other two are stirring up the silt swimming back and forth along the bottom and flashlights are swinging everywhere. We abort the dive, I do a slow ascent with my buddy and rejoin the other divers on the surface at around 15 minutes of elapsed total dive time. I agree with my buddy for us to do a dive without the other group, and we descend to 30m and have a nice 40 minute dive crawling up along a wall.
Again, with the minimal N2 loading of maybe 10 minutes at a maximum of 15m, I don't think there's a problem with restarting the dive without a surface interval.
My questions are:
1 - am I wrong in my assessment? Are any of these examples considered risky?
2 - it is my understanding that the major issue with descending after an ascent, is the possibility of gas bubbles being recompressed and passing over into the arterial blood flow, and that this is an important reason for the mandatory surface interval - is this correct? Are there other considerations?*
3 - Where do you draw the line?
A) In the first case: what are the limits of exposure and bounce you would be comfortable with?*
B) In the second case: how much of an exposure would you say warrants a mandatory surface interval?
4 - Or am I completely overthinking this out of proportion, surface intervals are not necessary when diving with a computer on NDL dives and bounces are not a problem?
*I expect that for deco dives this will be more problematic both in terms of available gas (if you were to redo any deco stops) and also in terms of higher load and more chance of bubbles - ie. dive your plan, if you drop something, let it go...
