PADI Deep Diver course- gas management

[Josh the diver]

Sure, so is teaching a drysuit class to someone who can't hook up their drysuit inflator.

I just find it interesting there is no required conservatism.

There is a potential that someone could be diving 100/100 or even 95/95 and then have a 60ft/min ascent with a computer that is expecting a 30ft/min ascent and be surfacing exceeding 100% gf, which sure isn't guaranteed bends, but defining a maximum GF or max bottom time at that depth would help define the risks for the agency.

not every one is diving a shearwater with customizable GF. there are a lot of computers that run different algorithms that don't use GF.

a lot of computers just have some form of a conservatism setting of low, medium, or high. which are all generally safe with just assuming more risk.

 

[crofrog]

not every one is diving a shearwater with customizable GF. there are a lot of computers that run different algorithms that don't use GF.

a lot of computers just have some form of a conservatism setting of low, medium, or high. which are all generally safe with just assuming more risk.

Sure that doesn't matter. Without some sort of maximum exposure defined for the class you're allowing individual instructors to define what the maximum risk is for the class. PADI defined half of it. Max Depth 130ft (40m), but not the other pieces which are time at depth, and minimum decompression time.

Those instructors could pick what the majority of the community would consider reasonable defaults like 40/85 (the default for medium on shearwater and Garmin) or something more conservative like the high conservatism settings. Generally speaking for new divers engaging in their first deep dives, a more conservative approach is probably warranted but it is instead left entire up to the instructors, and doesn't appear to be something that is covered in the academics for the class.

There are a lot of disagreements about what efficient decompression looks like, but there is I think little to no debate that that increased time under increased pressure increases the risk of DCS, and that DSC is the number 2 most common injury scuba diving.

 

[boulderjohn]

PADI defined half of it. Max Depth 140ft (40m), but not the other pieces which are time at depth, and minimum decompression time.

I am becoming thoroughly baffled. We are still talking about a NDL class, aren't we? If so, what does minimum decompression time have to do with things? PADI does define the maximum depths for those dives, but you don't have to reach those maximum depths, and since time at depth depends upon the depth, then of course is it sup to the instructor teaching the specific dive.

As for gradient factors and the like, the computer program starts with an algorithm that was determined through research to be acceptably safe, meaning it can be used as it. Yes, many people do use some means of making it even safer, but that is a personal preference, and that personal preference would make for an excellent discussion for dive planning.

 

[crofrog]

I am becoming thoroughly baffled. We are still talking about a NDL class, aren't we? If so, what does minimum decompression time have to do with things?

Do you materialize at the surface at the end of your bottom time?

If the answer is no, then the time spent ascending, and the time spent at the safety stop represent your decompression time. It has to do with the controlling the pDCS for a given exposure.

It would look something like this:

For the purposes of the PADI deep diver class

Max Depth	130ft (40m)
Maximum Bottom Time	10 min
Ascent speed (non-emergency)	30ft/min (10m/min)
Minimum safety stop time (non-emergency)	5 min

If you define those parameters you're basically ensuring that leading compartments M-value upon surfacing is ~75%, any use of nitrox would lower that number, as would any additional time at the safety stop. The ascent speed should be a target value because slower deeper would raise the M-value of the leading compartment and faster shallower would do the same.

 

[tursiops]

Without some sort of maximum exposure defined for the class you're allowing individual instructors to define what the maximum risk is for the class. PADI defined half of it. Max Depth 140ft (40m), but not the other pieces which are time at depth, and minimum decompression time.

You keep saying stuff like this, but it is not true.
The maximums are 130 ft for depth, and NDL according to the RDP or one's computer.
There is no decompression time allowed. It is an NDL class.

 

[Josh the diver]

deleted*

 

[crofrog]

if a safety stop is required to make the dive safe its not a NDL dive. its there to add more safety

Define safe as it relates to decompression.

 

[crofrog]

You keep saying stuff like this, but it is not true.
The maximums are 130 ft for depth, and NDL according to the RDP or one's computer.
There is no decompression time allowed. It is an NDL class.

Sorry my brain works in meters these days.

 

[tursiops]

If the answer is no, then the time spent ascending, and the time spent at the safety stop represent your decompression time. It has to do with the controlling the pDCS for a given exposure.

The time spent ascending is determined by the ascent rate and the depth; the ascent rate is a maximum of 18 m/min or what your computer says, whichever is slower; since nearly everybody is using computers, and the class ascends together, the ascent rate is in the vicinity of 10 m/min. The SS is 3-5 minutes, depending on the computer.

What about this don't you understand? What don't you like?

 

[boulderjohn]

if a safety stop is required to make the dive safe its not a NDL dive. its there to add more safety

Sorry, not the way it is defined. In fact, with more than a quarter century of diving behind me and two decades as a professional and two decades on ScubaBoard, I believe this si the first time I have ever seen anyone claim this to be true.