Lake Attersee fatality - Austria

[boulderjohn]

I assume that you could blow off your 3M, 6M and 9M stops and live to tell about it - If you are put in a chamber within 2hrs of ascending. It would still be a serious neurological hit, probably with long term damage including the loss of your sense of balance (you will never again pass the physical portion of a drunk driver roadside test).

I would not assume that. Without looking at dive planning software, I would assume that those stops are where most of the decompression time is done.

I have done a number of dives to about the 275 feet/84 meters, not much more than half of this planned dive, with total run times of about 2 hours. When I reach the 30 foot/9 meter stop, I am generally about half way through the dive, planning to switch over to oxygen at the next stop, which would greatly accelerate the speed of off-gassing and shorten the dive time. The 3 meter and 6 meter stops on oxygen are therefore the most important in total dive time; they are where you do most of your real decompressing. If I had to ascend immediately from the 40 foot/12 meter stop, I would not expect a pleasant outcome.

 

[Brad_Horn]

If you create a diveplan to 150 meters depth (where you return immediately), you can be back at 27m after 47 minutes runtime, which is what the article says. Total runtime could be around 165 minutes (depending on personal choices and chosen deco gasses, the elevation would add another half hour) and could be within the planned 180 minutes described in the article.

Assuming they were on rebreathers. And planning to be for the entire dive. With a water temp of 3-4’C. The pre-dive planning for their known scrubber duration would be interesting to see?

Not many systems available that could support this dive plan.... certainly even less with any safety margin factored in!

 

[Mod63]

The vulture has landed.

 

[michael-fisch]

I would not assume that. Without looking at dive planning software, I would assume that those stops are where most of the decompression time is done.

I have done a number of dives to about the 275 feet/84 meters, not much more than half of this planned dive, with total run times of about 2 hours. When I reach the 30 foot/9 meter stop, I am generally about half way through the dive, planning to switch over to oxygen at the next stop, which would greatly accelerate the speed of off-gassing and shorten the dive time. The 3 meter and 6 meter stops on oxygen are therefore the most important in total dive time; they are where you do most of your real decompressing. If I had to ascend immediately from the 40 foot/12 meter stop, I would not expect a pleasant outcome.

You are partly right. But if you had to blow off your deco, delaying these stops wpuld probably be survivable, as the Navy has been demonstrating for the last 70 years by using a chamber at the surface.
It would not be fun and with the normal delays between onset of symptoms and chamber treatment permanent damage cannot be excluded, but I don't expect that you will surface with a bloody froth coming out of your mouth followed by heart failure a couple of minutes later as would be expected if you had blown off the deeper stops.

When the **** hits the fan, try and make a decision that keeps you alive instead of killing yourself by ascending from 90' while blowing off more than 2 hrs of deco.

Michael

 

[boulderjohn]

I don't expect that you will surface with a bloody froth coming out of your mouth followed by heart failure a couple of minutes later as would be expected if you had blown off the deeper stops.

Where does this come from?

If I had some kind of gas emergency that forced me to drop some stops in favor of keeping others, it would absolutely be the deepest ones I would skip. Of course, that is all within reason--give me an example of skipping all the stops from 70 meters to 20 meters on a ridiculously long dive and that would be pretty bad, too. If I am diving with GFs of, say, 60/75 I would happily blow off stops that would take me to a GF lof of 100 before I blew off the shallow stops.

 

[Miyaru]

For anyone interested in technical diving and reading this topic:

There is not a single technical instructor that will ever tell you that you can skip the last three stops in a deco obligation. Never!

The most dangerous part of any dive, technical or recreational, is the last 10m/30ft to the surface, where the pressure is reduced by 50% (at sea level). And the last three stops are in that part.

 

[Vicko]

There is not a single technical instructor that will ever tell you that you can skip the last three stops in a deco obligation. Never!

I mean they will, as my instructor tactfully framed it:" if your dead anyway you may as well die on the surface where a body recovery is cheaper"
Blowing off those 3 stops after a 100+ meter dive is the same as jumping off of a 10 story building, kind of survivable but not really. Jumping in a chamber works but navy has those chambers 2 minutes away, not 2 hours.

 

[Bob DBF]

You are partly right. But if you had to blow off your deco, delaying these stops wpuld probably be survivable, as the Navy has been demonstrating for the last 70 years by using a chamber at the surface.

The delay, as @Vicko mentions above, is minutes rather than hours. If @Akimbo has the time, he could outline the procedure and timeline for you.

 

[Akimbo]

You are partly right. But if you had to blow off your deco, delaying these stops wpuld probably be survivable, as the Navy has been demonstrating for the last 70 years by using a chamber at the surface.

The delay, as @Vicko mentions above, is minutes rather than hours. If @Akimbo has the time, he could outline the procedure and timeline for you.

This would only apply if you had a chamber onboard with a fully prepared crew to man it. The procedure is called Surface Decompression using Oxygen, or Sur-D-O2. It is most often used with pure Oxygen water stops between 40 and 20' depending on the tables (US Navy or commercial). You are only allowed 5 minutes between leaving your last water stop and being at your at your decompression stop in the chamber on O2.

Omitted decompression would most likely put you on a treatment table 5 or 6, even if you could meet the 5 minute rule since water stops would be compromised. The dividing line between commercial Sur-D-O2 and treatment table 5 or 6 has gotten pretty fuzzy over the years. Many of the Sur-D-O2 tables I have seen and used look a lot more like treatment with O2 at 60' instead of 40' like most US Navy tables.

This is an image of a typical doublelock chamber:

This is a cross section diagram of the same chamber:

Hope this makes sense to everyone.

I have made up to 4 dives a day on Scuba, sometimes alternating HeO2 and Air, with "improvised" Sur-D-O2 tables. They included water stops at 20' on O2 fed from a skiff. The skiff was drifting (so divers weren't working too hard against the current) while the support boat with a chamber came alongside. The divers would leave 20' and be at 60' in the chamber in well under 5 minutes. It takes training and teamwork. Working depths were between 120 and 180'.

We had the chamber's inner lock already pressurized to 60' and the two divers would be blown down in the much smaller outerlock because the compressors usually weren't large enough to blow the innerlock down that fast. It is a pretty good procedure even with enough compressor capacity because rapid pressurization of a chamber gets really hot so the divers can go into the innerlock as soon as the hatch pops (pressure equalized). The innerlock was not only pressurized slower, it has had time to cool assisted by ventilating the chamber.

 

[Akimbo]

Here is a treatment table 5. We usually used pressurization rates as fast a possible for Sur-D-O2.