Evidence based guidelines on gas density planning

[max.horn]

Thank you for shearing this book! :)

[Simon Mitchell]

Hey Simon, great article again, thanks for sharing.


On page 45 Para 3, it talks about checking the linearity of the cells by ..."flushing the rebreather loop with 100% oxygen at a depth of 66ft (20m) prior to decent."

Comparatively speaking I'm very new to the RB world so I'm sure I've misinterpreted something, but wouldn't a flush at this depth result in a Po2 of 3bar and a serious dose of Hyperoxia?


Dave

Hi Dave,


It is Rich Pyle's paper so I don't know exactly what he intended, but I agree with you. I think this might be an editing mistake. He might have meant 20' rather than 20m, or something of the sort. I don't remember him saying 3ATA in his presentation.


It needs to be a depth / pressure that will clearly take the cells above the intended set point. 1.6 ATA will usually suffice for that. In addition, Paul Raymaekers (Revo Rebreathers) points out (and I agree with him) that the beginning of the dive is not the best time to challenge cells because there have been a number of clear examples of cells tracking PO2 well at the start of a dive, but becoming currently limited after a longer period of exposure to 'stress' (high PO2, temperature, humidity). He advocates testing them with an oxygen flush toward the end of a dive, which then becomes a test for the cells prior to the next dive (if you see what I mean). You could do both of course (test at beginning and end of a dive).


Simon M

[Nad]

...that the beginning of the dive is not the best time to challenge cells because there have been a number of clear examples of cells tracking PO2 well at the start of a dive, but becoming currently limited after a longer period of exposure to 'stress' (high PO2, temperature, humidity). He advocates testing them with an oxygen flush toward the end of a dive, which then becomes a test for the cells prior to the next dive (if you see what I mean). You could do both of course (test at beginning and end of a dive).
Simon M

Hi Simon,
Thanks for this I couldn't write it better. It's gonna probably help understanding that the cells linearity check is not a warranty!
Nad

[Mark Chase]

Hi Dave,


It is Rich Pyle's paper so I don't know exactly what he intended, but I agree with you. I think this might be an editing mistake. He might have meant 20' rather than 20m, or something of the sort. I don't remember him saying 3ATA in his presentation.


It needs to be a depth / pressure that will clearly take the cells above the intended set point. 1.6 ATA will usually suffice for that. In addition, Paul Raymaekers (Revo Rebreathers) points out (and I agree with him) that the beginning of the dive is not the best time to challenge cells because there have been a number of clear examples of cells tracking PO2 well at the start of a dive, but becoming currently limited after a longer period of exposure to 'stress' (high PO2, temperature, humidity). He advocates testing them with an oxygen flush toward the end of a dive, which then becomes a test for the cells prior to the next dive (if you see what I mean). You could do both of course (test at beginning and end of a dive).


Simon M

Simon

Isn't testing the cells at the end of the dive closing the door after the horse has bolted?


If i am plannig 2-4 hours in the water ill test cells before (on the boat) at the begining (at 8m to 1.8pp02 and at the bottom of the shot comparison with known dill and PP02 readout) during ( mini 02 manual spikes to ensure 1.4PP02+ is acheivable and dill flush PP02 checks if i get results I am not happy with) and after the dive 02 inject at 9m prior to ascent to 6 to ensure reading over 1.6)

Finding out my cells are limited at the end of the dive seems prety pointless to me

I needed to know this 2 hours ago when I was on the bottom showing 1.3 across the board.

ATB

Mark

[oya]

Simon

Isn't testing the cells at the end of the dive closing the door after the horse has bolted?

At the end of this dive I'm testing my cells for the next dive.

During this dive I'm testing at the beginning and (usually... sometimes... when I'm at a depth where the math is easy) in the middle.

[exposure]

Mark, if the test failed at the end of the dive you can either change the cell for the next dive or have a beer a skip the next dive :)

oya, on the petrel or perdix you can show the PPO2 from your diluent at current depth, so no math here :)

[jneves]

Or use a Poseidon Seven, and you don't have to guess anything!

JNeves

[deepdave]

Or use a Poseidon Seven, and you don't have to guess anything!

JNeves

The report certainly does labour the benefits of the Poseidon.

[Mark Chase]

Mark, if the test failed at the end of the dive you can either change the cell for the next dive or have a beer a skip the next dive :)

oya, on the petrel or perdix you can show the PPO2 from your diluent at current depth, so no math here :)

Absolutly, and thats why I do an end of dive test but if they failed during the dive I may not be arround to do the next dive which is why i test during the dive as well.

[Mark Chase]

Or use a Poseidon Seven, and you don't have to guess anything!

JNeves

I am still not convinced this is true but stand to be proved wrong. the in flight testing offered by the unit is IMHO leaving a LOT of unanswered questions and once again puts the diver at the mercey of reliable automation.

As I have said before massive companies have spent millions on R&D for stuff that still fails. Just look at car recals

The diving industry is tiny in comparison and I have low confidence in the compleetness of any R&D prior to market of its systems.

The famous Apoc situation with its pontificating about CE standards and rigerous testing is demonstration in point when they released to market a faulty component.

Perhaps I am a ludite but I take my own life prety seriously if only for my familys sake so I need to feel I have done all I can to minimise the risks

I like stuff you can touch, feel and hit with a hammer

When somone says 2+2 = 4 I only have 100% confidance when I can see two apples next to two apples and I can count 4

When somone tells me to have faith in a gizmo and my life is on the line, I will always look for a 2 + 2 way of confirming this if I possably can

I dont mind being called a silly old fart just as long as I can reach the "old" bit

ATB