Wreck of Lowrance event this morning...Any news?

[poseident]

"ascending too slowly--often far too slowly--was the most common problem with rebreather divers"

John, what do you think is driving this? People without strong core diving experience jumping to rebreathers too soon? Not that, but just over-reliance on "dive the computer?" Lack of guidance in training materials?

 

[boulderjohn]

"ascending too slowly--often far too slowly--was the most common problem with rebreather divers"

John, what do you think is driving this? People without strong core diving experience jumping to rebreathers too soon? Not that, but just over-reliance on "dive the computer?" Lack of guidance in training materials?

I don't know.

Perhaps it is a holdover from NDL diving, where ascending too slowly is not an issue.

As for computer reliance, the first time I was really aware of this issue was in a decompression dive where no computers were involved. In this case, the divers were using ratio deco, using bottom timers and one computer in gauge mode (fortunately). They knew when they needed to leave the bottom, where they needed to do their first deep stop, and how long they needed to be at each stop. When they got bent, they looked at their dive profile on the computer in gauge mode and discovered they had (among other errors) taken about 3-4 times as long as they should have to get to that first stop. If they had been diving with computers, the computers would have adjusted to all their errors. Because they did not know they had made those errors until they downloaded the profile, they did not know that the dive they did was different from the dive they thought they had done.

 

[Johnoly]

I agree with @boulderjohn there is too much "follow the computer's colored lights" and not enough continuing education to understand what is really happening with your tissues. When you sit in the DEMA DAN's seminars this is discussed many times.

Tissue loading is a constantly moving process
Tissue over saturation is a point in time.

For those of us that push the limits of either deco or dive on the edge of NDL,, the quicker (& safer) we can get out of the deep and slow down that Tissue loading is critical on how the rest of our afternoon is going to go. {I'm ignoring helium, etc) But divers should have a variable ascent rate from the deep triple digits stuff that is very different from the last 30ft to surface. If you are moving at a snail's pace going up from 130 to 100ft you are racking up tissue loading quickly and very well can hit the 'over saturation point'. Many computers will then penalize you on your next tank(s) bottom time.

 

[scubadada]

...If you are moving at a snail's pace going up from 130 to 100ft you are racking up tissue loading quickly...

If you are using a dive computer, it will be reflected in the NDL or deco time

 

[beldridg]

I just looked at 5 of my most recent deeper dives (250'-300') and calculated that my actual average ascent rate is about 30fpm to the first deco stop. There is a little bit of delay because I'm usually turning off camera video lights, picking up a strobe, etc. while somewhat on the move but not too bad.

This is a little bit off topic from the original thread, but are people still using the 60fpm below a certain depth and then 30fpm above that depth for deco dives (can't remember what the standard is anymore)?

I just usually stick with about 30fpm. I find it to be a good ascent rate where I can vent my counter lung, maintain a PO2, vent my drysuit, vent my wing, etc. while not adding on additional deco.

I also looked at the "efficiency" of my ascents by checking the TTS when I left the bottom and the TTS when I got to the first deco stop (and the PO2 was stabilized) to verify it had decreased or stayed the same and not increased. That was the case for all 5 dives I checked.

I'm curious what others in drysuits + rebreathers are doing in practice?

- brett

 

[clownfishsydney]

This is a little bit off topic from the original thread, but are people still using the 60fpm below a certain depth and then 30fpm above that depth for deco dives (can't remember what the standard is anymore)?

I usually come up quickly from the bottom (around Sydney, 45 to 50 metres) till I get to about 20 metres and then slow to 9 m/s (30 feet/sec). Have been doing this for 30 years.

 

[poseident]

I've known people that try to ascend at a rate that avoids seeing their ascent graph tick up--assuming slower is better. More tissue loading increases risk. Sure, there are other variables, but if there's a general trend toward a behavior that adds risk, I think that's worth discussing. This kind of behavior was the exception 20 years ago, but it sounds like it might be more common now.

"If you are using a dive computer, it will be reflected in the NDL or deco time"

Scubadada is correct, but I think the point is, "should you avoid it when possible anyway." Amex will let me pay my card balance in monthly installments, but I'd only do that in an emergency, as the "fee loading" is not desirable!

 

[poseident]

I just looked at 5 of my most recent deeper dives (250'-300') and calculated that my actual average ascent rate is about 30fpm to the first deco stop. There is a little bit of delay because I'm usually turning off camera video lights, picking up a strobe, etc. while somewhat on the move but not too bad.

This is a little bit off topic from the original thread, but are people still using the 60fpm below a certain depth and then 30fpm above that depth for deco dives (can't remember what the standard is anymore)?

I just usually stick with about 30fpm. I find it to be a good ascent rate where I can vent my counter lung, maintain a PO2, vent my drysuit, vent my wing, etc. while not adding on additional deco.

I also looked at the "efficiency" of my ascents by checking the TTS when I left the bottom and the TTS when I got to the first deco stop (and the PO2 was stabilized) to verify it had decreased or stayed the same and not increased. That was the case for all 5 dives I checked.

I'm curious what others in drysuits + rebreathers are doing in practice?

- brett

That sounds too much like work to me Brett! More power to you sir, and kudos for going back and evaluating your metrics.

 

[missionmtb]

I don't think there is such a thing as ascending too slowly, only not planning your dive for your planned/typical ascent rate. I can speak from personal experience that 30 fpm has felt uncomfortably fast or overwhelming sometimes, especially early on diving rebreather and especially when carrying gear. With experience I got a better feel for buoyancy adjustments necessary to avoid being out of control at higher ascent rates, but IMHO managing 3 air spaces on ascent can be tough, especially when you're hustling.

I know in multi-deco you can plan for a slower descent/ascent rate, but this only occurs to me now on reflection that i might actually want to do this. On shorter dives the racked-up deco from a slow rate has been minimal. The bigger and bigger the dive gets though...

The descent rates I've seen from Florida negative entries I don't think I'll ever get used to...

TL-DR Plan your dive, dive your plan (including depth change rates)

 

[boulderjohn]

I don't think there is such a thing as ascending too slowly, only not planning your dive for your planned/typical ascent rate

Ascending slower than the standard rate is similar to doing deep stops--they will both increase your on-gassing in the slower tissues. Ascending slowly on NDL dives has not been shown to have an adverse effect, but research on deep stops on decompression dives has shown that they are not the best course of action. If you do them, you are essentially adding to bottom time and requiring longer shallow decompression stops.