Do you check your cells at 6m?

Matt Reed

Matt Reed

New Member
Encouraged by this thread http://www.ccrexplorers.com/showthread.php?t=16383&highlight=linearity+pelagian

Can people put forward their dive procedure between the surface and 6m, and then downwards please.

I'm just interested to know how many different procedures there are. Currently diving with a Hammerhead diver who has not been trained or has any idea about checking cells at 6m for linearity.

So what do you think is "industry standard"?

And what do you actually do?

Thanks.
 
I dont flush at 6m, I spike my cells several times at depth instead. Usually on a hot drop, my cells will spike anyways, so I've already checked 1.6.
 
Turn on computer & allow to reach and hold 0.7 set point

Pure 02 flush manualy and ensure cells read at least 0.98

Stand up and walk to gate then blind manual flush 02 check hand set if possable but often two hands needed to stay uprght and sun too bright to check HUD

Jump in check PP02 and swim to shot

Grab shot and check PP02 flush if required for 100%

Get to 8m stop and check PP02 is over 1.6. If not flush to ensure PP02 can read over 1.6

Vent, suck in dill and decend with computer on low set point

Check PP02 on the way down

Hit max depth and check PP02 against Dill PP02 for that depth. If in error then flush dill to ensure cells reading properly

Switch to high set point and watch cells hit 1,3

Start dive

Ocasionaly spike 02 to ensure cells read over 1.3


PS 20m or 120m same drill every time.



ATB

Mark
 
Perfect. Thanks Mark.

So if I am seeing things right this is what most people do? Either this or do nothing? Am I right ?

Cheers.
 
I do very similar to Mark but I am on an MCCR.

Sitting on the bench ramp loop to as close to 1bar (98% ish usually as have SW electronics)

Get up and walk to jump point, if in doubt adding more O2, check for close to 1bar as I jump.

Check once more at shot buoy or on surface if direct descent.

Stop at 6-7mtr, and if Dil has been injected dump and O2 flush or just thumb in more O2 to spike sensors while bubble/buddy check.

(So basically everything from turn on to 6mtrs is pure O2, any issue at this point bin the dive- I only ever decide whether the dive is on at 6mtrs)

At the bottom dil check then reestablish nominal set point and go diving.


Obviously this process is interspersed with other activities, scooters, deco stations, faffing buddies etc but my rule is O2 only till its safe not to be. Messing about near the surface when checking PPO2 can be hard is alot safer with pure O2 loop than unknown.
 
First of all I'm a cave diver with dual mCCR (joki)

I start my dive with O2 (100%) and always stop at 6m to check my cells.

I check my cells on my principal mCCR until 1.4/1.5 then I switch on my second mCCR and do the same thing,of course I flush my 2 mCCR during my check

After that,I turn off my CMF on my second mCCR and open the diluant valve (to avoid squeeze into my mCCR during the descent and to avoid high PPO2 at bottom)

Then I switch on my principal mCCR open my diluant valve,check my cell ,adjust my PPO2 on my computers (2 liquivision X1) and start my dive.

It's seems a little bit long but in fact it's last 5 minutes.

Cheers

Manu
 
Jeff Pack said:
I dont flush at 6m, I spike my cells several times at depth instead. Usually on a hot drop, my cells will spike anyways, so I've already checked 1.6.
Click to expand...

Without a known gas at a known depth, how is this "checking" your cells?


Sent from my rebreather using Tapatalk
 
Matt Reed said:
Perfect. Thanks Mark.

So if I am seeing things right this is what most people do? Either this or do nothing? Am I right ?

Cheers.
Click to expand...

well.. short or long story... and for some maybe controversial ..


in most cases, oxygen spike to 1.6 at the start of a dive does not tell you anything regarding current limiting of your sensors !

because:

oxygen sensors have a capability to 'recover' from current limiting if you have not used them for a period of time (can be a day, a week, a month)

if your sensors are current limited in some way, they will still perform correctly at the start of a dive, they have enough 'current capacity' stored to funtion for a moment, but the current limiting behaviour will start to show up after.. 20 minutes, or an hour or... depending on the state of the sensor

so good practice is to check your sensors sometimes during a dive, and specially at the end of the dive, at 9 or 6 meter, to check if they still ramp up fast to > 1.6

if you want to know more about this, come to my presentation, eurotec, DEMA, oztek: Understanding Oxygen Sensors Part II: the MYTH!

paul
 
paulraymaekers said:
well.. short or long story... and for some maybe controversial ..


in most cases, oxygen spike to 1.6 at the start of a dive does not tell you anything regarding current limiting of your sensors !

because:

oxygen sensors have a capability to 'recover' from current limiting if you have not used them for a period of time (can be a day, a week, a month)

if your sensors are current limited in some way, they will still perform correctly at the start of a dive, they have enough 'current capacity' stored to funtion for a moment, but the current limiting behaviour will start to show up after.. 20 minutes, or an hour or... depending on the state of the sensor

so good practice is to check your sensors sometimes during a dive, and specially at the end of the dive, at 9 or 6 meter, to check if they still ramp up fast to > 1.6

if you want to know more about this, come to my presentation, eurotec, DEMA, oztek: Understanding Oxygen Sensors Part II: the MYTH!

paul
Click to expand...

Of course, if you aren't going to dive again for two months, testing at the end of the dive ain't telling you much either. I personally have found that the hassle of starting with pure O2, taking that to 6m and then trying to unspike as we rush to the bottom is a royal PITA compared to an O2 flush at the last stop where I'm not going to go any higher because of the depth.

Guess the only way to really be sure, though, is pop the cells out of the head and into a checker for half an hour at pressure if you haven't dived them for a while.
 
Jeff Pack said:
makes sure I'm not current limited. Like Paul states above...
Click to expand...

What I am saying is, who cares if it goes to 1.6 if you don't know what it should be (known gas at a known depth)?

Paul, and every other post I have read, talks about doing a verified check- the only way to know if your cells are current limited is to know what value they should be. Just because my cells can hit 1.6 doesn't mean I'm not having major problems with them (what if my actual PO2 was 2.2?)

Am I missing something?

To get back to the OP, I simply flush with O2 after my pre-breath and only inject O2 until I hit 6m. I also do a O2 flush and cell check on my ascent at 6m. 2 point check on just about every dive. I also check my cells in a pressure regularly.


Sent from my rebreather using Tapatalk
 
My Method is this,
descend to target depth on low setpoint, once I reach bottom my po2 should be same as the dil,(dil po2 is above low setpoint) if it is switch to high setpoint, watch and listen once high setpoint is achieved with out suspicion I manually boost to somewhere above my setpoint to check that all cells will go there. initial verification is done against a known gas, my dil.
What Paul said about giving time for cells to work a bit is an extremely important point, you wont get an idea of correct reaction until the loop has warmed up and is humidified.
 
CCR Josh said:
What I am saying is, who cares if it goes to 1.6 if you don't know what it should be (known gas at a known depth)?

Paul, and every other post I have read, talks about doing a verified check- the only way to know if your cells are current limited is to know what value they should be. Just because my cells can hit 1.6 doesn't mean I'm not having major problems with them (what if my actual PO2 was 2.2?)

Am I missing something?
Click to expand...

You've already calibrated, so you already know your cells read 1.0 PPO at some given mv.

AFAIK, the only way you could get a reading of 1.6 and a real PPO of 2.2, would be some sort of horrifically non linear cell performance past 1.0 that wouldn't show as current limited. I'll have to leave that possibility to the experts on sensors. And that would also assume all 3 sensors failed the same non linear way, so I wouldn't have some idea something wanky was going on.

Now I do know that sometimes a cell will flare high before failing (My instructor had this happen to him), but that's the opposite where PPO was lower, and cell read high.
 
paulraymaekers said:
well.. short or long story... and for some maybe controversial ..


in most cases, oxygen spike to 1.6 at the start of a dive does not tell you anything regarding current limiting of your sensors !

because:

oxygen sensors have a capability to 'recover' from current limiting if you have not used them for a period of time (can be a day, a week, a month)

if your sensors are current limited in some way, they will still perform correctly at the start of a dive, they have enough 'current capacity' stored to funtion for a moment, but the current limiting behaviour will start to show up after.. 20 minutes, or an hour or... depending on the state of the sensor

so good practice is to check your sensors sometimes during a dive, and specially at the end of the dive, at 9 or 6 meter, to check if they still ramp up fast to > 1.6

if you want to know more about this, come to my presentation, eurotec, DEMA, oztek: Understanding Oxygen Sensors Part II: the MYTH!

paul
Click to expand...


!: OK if you say so, but if they cant even go above 1.6 at the start of the dive you know your in trouble. Frankly if they can hit 1.7 -1.8 I am prety sure they will do 1.3 for a little while

2: Thats why you spike several times mid dive to ensure they can still read above 1.3



Doing it is better than not bothering at all.


ATB

Mark
 
Last edited:
Mark Chase said:
!: OK if you say so, but if they cant even go above 1.6 at the start of the dive you know your in trouble. Frankly if they can hit 1.7 -1.8 I am prety sure they will do 1.3 for a little while

2: Thats why you spike several times mid dive to ensure they can still read above 1.3
Mark
Click to expand...

I can show you test graphs where you spike 2.0 at start, and after 30 minutes, you can't get 1.3 anymore

point 2: fully agree that this is a good practice
 
Any chance you will give this new Part 2 talk at the Asia InternationalRebreather event in a September?

Hope so! :)

paulraymaekers said:
well.. short or long story... and for some maybe controversial ..


in most cases, oxygen spike to 1.6 at the start of a dive does not tell you anything regarding current limiting of your sensors !

because:

oxygen sensors have a capability to 'recover' from current limiting if you have not used them for a period of time (can be a day, a week, a month)

if your sensors are current limited in some way, they will still perform correctly at the start of a dive, they have enough 'current capacity' stored to funtion for a moment, but the current limiting behaviour will start to show up after.. 20 minutes, or an hour or... depending on the state of the sensor

so good practice is to check your sensors sometimes during a dive, and specially at the end of the dive, at 9 or 6 meter, to check if they still ramp up fast to > 1.6

if you want to know more about this, come to my presentation, eurotec, DEMA, oztek: Understanding Oxygen Sensors Part II: the MYTH!

paul
Click to expand...
 
Mark Chase said:
!
Doing it is better than not bothering at all.


ATB

Mark
Click to expand...

Not really - it doesn't provide any information other than at the start of the dive they read over 1.6 which has no impact later in the dive so it lures you into a false sense of security that the cells must be OK as I tested them at start of dive. All of these spikes and pots do nothing except verify cell function at time (and conditions / duration) and not the most important time, ie on the dive, you'd be much better off just throwing cells away 1 year after manufacture.
 
Bobjr said:
Not really - it doesn't provide any information other than at the start of the dive they read over 1.6 which has no impact later in the dive so it lures you into a false sense of security that the cells must be OK as I tested them at start of dive. All of these spikes and pots do nothing except verify cell function at time (and conditions / duration) and not the most important time, ie on the dive, you'd be much better off just throwing cells away 1 year after manufacture.
Click to expand...

I'd have to think that knowing they work properly at the beginning of the dive is better than not being sure they work at the beginning of the dive and just hoping instead? What period of time are we taking as ok after the test - 10 seconds, 10 minutes? Or are you suggesting not bothering with any tests and just diving?
 
Matt Reed said:
I'd have to think that knowing they work properly at the beginning of the dive is better than not being sure they work at the beginning of the dive and just hoping instead? What period of time are we taking as ok after the test - 10 seconds, 10 minutes? Or are you suggesting not bothering with any tests and just diving?
Click to expand...

I am suggesting knowing your cells, watching during calibration, spiking above set point on dive occasionally and most importantly not cutting corners on replacing cells 12mo after manufacture but not luring myself into a false sense of security and wasting time checking at 6m at start of dive.
 
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