PADI Deep Diver course- gas management

[Cthippo]

Please forgive me, I'm confused by these seemingly contradictory statements. Is there "plenty of data" or isn't there?

There is enough data to be clear that it does happen, but not enough to really understand the risk.

 

[tursiops]

There is enough data to be clear that it does happen, but not enough to really understand the risk.

Bingo.
I've got 3300+ logged dives over many years, in most of the world, LOB, boat, shore, recreational, scientific, and technical.
So I've been in the company of at least 35-40K dives, between my buddy and the dive group I'm with.

• I've seen exactly one DCS case; it was a new diver on a 70 ft short dive....but with a massive PFO discovered after the fact. She is fine now, but not diving anymore.
• I've seen exactly one out-of-gas instance, managed perfectly by the diver the OOG person swam up to
• I've had exactly one OOG incident myself, in a cave (a second stage fell off my sidemount tank hose), with an instructor, and ending up taking her reg from her mouth for a few breaths while I sorted myself out.
• I've seen exactly two inadvertent buoyant ascents from 80 ft depth, with no residual after effects.
• I've seen exactly one HP hose rupture at depth (my wife) and she and I went together to the surface, slowly, each preathing from our own reg.

Kind of hard to do risk analysis....

 

[jadairiii]

Please forgive me, I'm confused by these seemingly contradictory statements. Is there "plenty of data" or isn't there?

No need to be confused. In the beginning, divers had no NDL tables. Then, USN developed their NDL tables, and life was good. But for some strange and unknow reason (data?) the large scuba instruction agencies just randomly cut anywhere from 5 to 10 min off those Navy tables. And then we all got computers, early computers used all the same algorithms that the Navy and large scuba instruction agencies used, and life was even better, well, maybe not. The early multi-level computers were a tad liberal (more data), like the SOS, Edge, Oceanic air computer. And again, for some strange and unknow reason, computers became more and more conservative. Ever dive an early Suunto computer?

All of this change could have been merely random....or lots of data. My "problematic" comment referred to those DSC incidences that were never reported. And I for one, am guilty of this.....

Anyway, whatever. But as stated, The Physiology and Medicine of Diving, by Bennett is a good read.

I would have responded sooner, but I was diving this weekend.

 

[boulderjohn]

Then, USN developed their NDL tables, and life was good. But for some strange and unknow reason (data?) the large scuba instruction agencies just randomly cut anywhere from 5 to 10 min off those Navy tables.

The reasons for the changes to the tables are well known, based on extensive published scientific research.

The problem for sport divers using the US Navy tables was that surface intervals were arbitrarily based on the 120 minute compartment--no research was used to make that decision. Those tables also had few pressure groups, leading to the need to do a lot of rounding. As a result, surface intervals were very long, making the typical 2-tank dive schedule we know today impossible. This was just fine for the US Navy, because their divers only did one dive a day anyway.

Accordingly, PADI funded extensive research on this topic, using Doppler bubble imaging to measure venous gas bubbles. (This is the research you apparently misattributed to DAN earlier in the thread.) That research indicated that for the vast majority of NDL dives done by typical sport divers, the 40 minute compartment could safely control the surface interval. They decided to use the 60 minute compartment to be safe. They also roughly doubled the pressure groups so there would not be as much rounding. Finally, they shortened the NDL times a little. That combination led to a table (the Recreational Dive Planner) with surface intervals that enabled the 2-tank dive schedules used around the world today.

At the same time, they experimented with multi-level dives and created a dive table (the wheel) that could be used to plan a multi-level dive and thus greatly expand bottom times.

 

[inquis]

But for some strange and unknow reason (data?) the large scuba instruction agencies just randomly cut anywhere from 5 to 10 min off those Navy tables.

For the record, this was due to a desire for repetitive NDL diving with shorter surface intervals.

I'm glad you got to dive this weekend... I didn't.

 

[tursiops]

No need to be confused. In the beginning, divers had no NDL tables. Then, USN developed their NDL tables, and life was good. But for some strange and unknow reason (data?) the large scuba instruction agencies just randomly cut anywhere from 5 to 10 min off those Navy tables. And then we all got computers, early computers used all the same algorithms that the Navy and large scuba instruction agencies used, and life was even better, well, maybe not. The early multi-level computers were a tad liberal (more data), like the SOS, Edge, Oceanic air computer. And again, for some strange and unknow reason, computers became more and more conservative. Ever dive an early Suunto computer?

All of this change could have been merely random....or lots of data. My "problematic" comment referred to those DSC incidences that were never reported. And I for one, am guilty of this.....

Anyway, whatever. But as stated, The Physiology and Medicine of Diving, by Bennett is a good read.

I would have responded sooner, but I was diving this weekend.

Not sure where you are getting your I formation, but some is incomplete and some is just wrong.

 

[tursiops]

The reasons for the changes to the tables are well known, based on extensive published scientific research.

The problem for sport divers using the US Navy tables was that surface intervals were arbitrarily based on the 120 minute compartment--no research was used to make that decision. Those tables also had few pressure groups, leading to the need to do a lot of rounding. As a result, surface intervals were very long, making the typical 2-tank dive schedule we know today impossible. This was just fine for the US Navy, because their divers only did one dive a day anyway.

Accordingly, PADI funded extensive research on this topic, using Doppler bubble imaging to measure venous gas bubbles. (This is the research you apparently misattributed to DAN earlier in the thread.) That research indicated that for the vast majority of NDL dives done by typical sport divers, the 40 minute compartment could safely control the surface interval. They decided to use the 60 minute compartment to be safe. They also roughly doubled the pressure groups so there would not be as much rounding. Finally, the shortened the NDL times a little. That combination led to a table (the Recreational Dive Planner) with surface intervals that enabled the 2-tank dive schedules used around the world today.

At the same time, they experimented with multi-level dives and created a dive table (the wheel) that could be used to plan a multi-level dive and thus greatly expand bottom times.

The full report is here:

Info - The DSAT Recreational Dive Planner (RDP), 1994

Document Name: Development and validation of no-stop decompression procedures for recreational diving: The DSAT Recreational Dive Planner Authors: R.W. Hamilton, Raymond E. Rogers, Michael R. Powell, Richard D. Vann, with Richard Dunford, Merrill P. Spencer, Drew Richardson Attached is the...

scubaboard.com

 

[wetb4igetinthewater]

Where did you get the ones you are quoting?
I'm hesitant to post copyrighted material in its entirety.

I'll do it for you.

Deep Dive OnePerformance Objectives
By the end of Deep Dive One, student divers should be able to, with a buddy and withinstructor guidance as appropriate:
1.Plan and manage gas use, including determining turn pressure, ascent pressure and reserve pressure. Establish no stop and dive time limits.
2.Descend using a line, wall or sloping bottom.
3.Compare changes in color at the surface and at depth.
4.Compare a dive computer (or depth gauge) reading to another diver’sdepth reading.5.Ascend at a rate not to exceed 18 metres/60 feet per minute using a dive computer (ordepth gauge and timing device).
6.Make a safety stop at 5 metres/15 feet for at least three minutes.

1, 2, 5, & 6 are all out of open water. 3 & 4, no skills involved

Deep Dive Two
Performance Objectives
By the end of Deep Dive Two, student divers should be able to, with a buddy and withinstructor guidance as appropriate:
1.Execute a free descent using a reference line, wall or sloping bottom as a visual guide only.
2.Describe and record the changes that occur to three pressure-sensitive items while atdepth.
3.Perform a navigation swim with a compass away from, and back to, the anchor or thereference line. (One diver navigates away from, the other navigates back to, the referenceline for a distance of between 10 and 20 kick cycles, depending on visibility.)
4.Perform an ascent using a reference line, wall or sloping bottom as a visual guide only.
5.Ascend at a rate not to exceed 18 metres/60 feet per minute using a divecomputer (or depth gauge and timing device).
6.Make a safety stop at 5 metres/15 feet for at least three minutes without physicallyholding on to a reference line for positioning

1, 3, 4, 5, 6 are all out of open water. No skills involved with 2.

Deep Dive Three
Performance Objectives
By the end of Deep Dive Three, student divers should be able to, with a buddy and withinstructor guidance as appropriate:
1.Execute a descent using a reference as a tactile or visual guide (line, wall or slopingbottom).
2.Compare the amount of time needed to complete a task on the surface and at depth.
3.Perform an ascent using a reference as a tactile or visual guide (line, wall or slopingbottom).
4.Ascend at a rate not to exceed 18 metres/60 feet per minute using a dive computer (ordepth gauge and timing device).
5.Perform an eight-minute simulated emergency decompression stop at 5 metres/15 feetbefore surfacing, while breathing from an emergency air source for at least one minute of the total time

1, 3, 4 are out of open water. While 2 is supposed to indicate narcosis, there is no industry or even PADI standard way of doing it. Many people can do math problems at the same speed. 5 is basically out of open water, just extending the time.

Deep Dive Four
Performance Objectives
By the end of Deep Dive Four, student divers should be able to, with a buddy and withinstructor guidance as appropriate:
1.Execute a descent using a reference as a tactile or visual guide (line, wall or slopingbottom).
2.Complete an underwater tour of the area.
3.Perform an ascent using a reference as a tactile or visual guide (line, wall or slopingbottom).
4.Ascend at a rate not to exceed 18 metres/60 feet per minute using a dive computer (ordepth gauge and timing device).
5.Make a safety stop at 5 metres/15 feet for at least three minutes.

All of these are open water.

I love these discussions where we get into the details and show what little value there is in con ed.

 

[crofrog]

3.Compare changes in color at the surface and at depth.
2.Describe and record the changes that occur to three pressure-sensitive items while atdepth.

That doesn't seem very valuable just in general

4.Ascend at a rate not to exceed 18 metres/60 feet per minute using a dive computer (ordepth gauge and timing device).

Interesting that this is the acceptable ascent rate for the class.

What gradient factors or decompression algorithms are prescribed for the class?

How does PADI mitigate the risks that come from breathing a gas that is at the maximum limit of 6.2g/l recommended by the work of Anthony and Mitchell?

 

[wetb4igetinthewater]

What gradient factors or decompression algorithms are prescribed for the class?

How does PADI mitigate the risks that come from breathing a gas that is at the maximum limit of 6.2g/l recommended by the work of Anthony and Mitchell?