SCR - how does it works

[Pierre Farrugia]

Hello ,

I heard many times that in an emergancy on a CCR one can dive it as a SCR. As I don't have any idea as how does a SCR work, can anyone explaine ? Why you mention low PPo2 when diving air as diluent, what are it's dangers.

Regards

Pierre

[divetheworld]

I dont mean to be picky but if your waiting for your YBOD then you must have done a training programme? This should have been part of the course - is it not?

for more info try this link - http://www.bishopmuseum.org/research...autz97/rb.html

[Pierre Farrugia]

Originally Posted by divetheworld

I dont mean to be picky but if your waiting for your YBOD then you must have done a training programme? This should have been part of the course - is it not?

for more info try this link - http://www.bishopmuseum.org/research...autz97/rb.html

Hello,

You are right and my unit will be here next week and will do course as soon it is here. As a complete beginner I tought that this will be covered in MOD 2 and not one!

Thanks

[gobfish1]

Originally Posted by Pierre Farrugia

Hello,

You are right and my unit will be here next week and will do course as soon it is here. As a complete beginner I tought that this will be covered in MOD 2 and not one!

Thanks

its in MOD 1

tell s you how to get min bag and what happens if you dont ,
have a read its all there,,,

Good Luck with your YBOD

steve G

[Mark Chase]

Originally Posted by Pierre Farrugia

Hello ,

I heard many times that in an emergancy on a CCR one can dive it as a SCR. As I don't have any idea as how does a SCR work, can anyone explaine ? Why you mention low PPo2 when diving air as diluent, what are it's dangers.

Regards

Pierre

Semi closed is an option that provides a constant flow of 02 into the breathing loop giving a fixed gas mix rather than a dynamic set point. Basically it’s Nitrox diving on a loop. The loop is not sealed so the overpressure gas is vented off thus reducing the CO2 content of the mix and putting less strain on the scrubber. The KISS is a half way house between SCR and CCR. It is closed circuit but it also works on a constant flow of 02 into the loop. However this is a space shuttle to the SCR's bus and it injects exactly the right amount of 02 to be fractionally below the metabolic usage of the diver. The increased depth = increased density of the gas and there for less 02 can get through the KISS valves orifice. Hay presto; a dynamic depth related set point without the electronics. Utterly brilliant, if you ignore the obvious problems. The Inspiration et all, are dynamic set point closed loop CCR's that are the cutting edge of the concept.

Electronically monitored gas loop and solenoid injection of 02 based on voting logic to maintain a dynamic user variable set point. The dogs bollox until the electronics go all technical on you. THEN one option is to use the 02 decay curve on your diliuent. This is referred to as going semi closed. You breathe the loop for four breaths on an ever decreasing PP02 and then you breath out through your nose thus venting the gas and sucking in fresh gas via the ADV or manual inject. The process is then repeated until you are home. Using this system a 3ltr becomes a 12ltr. It is very easy to do and can get you out of a lot of trouble.

ATB

Mark Chase

[Pierre Farrugia]

Hello again,

What failure mode can happen for a YBOD diver to switch SCR ?

[Mark Chase]

Originally Posted by Pierre Farrugia

Hello again,

What failure mode can happen for a YBOD diver to switch SCR ?

Total loss of 02
Failure of hand sets or 02 sensors resulting in loss of PP02 tracking
Suspected Co2 buildup / scrubber failure but this includes a dill flush first.

I am strugling to think of others but I am sure someone more experianced than I will let you know

ATB

Mark Chase

[nigelH]

Originally Posted by Mark Chase

Total loss of 02
Failure of hand sets or 02 sensors resulting in loss of PP02 tracking
Suspected Co2 buildup / scrubber failure but this includes a dill flush first.

I'll go with those.

Basically it is first call for any condition where you can't inject O2 into the loop either because you haven't got any or because you can't measure the ppO2. Semi-closed mode is better than OC as you now have a gas extender.
If the scrubber is gone, is going or is just suspect semi-closed means you are dumping loop volume and 'helping' the scrubber. I suspect that at 3:1 you could survive a complete scrubber outage.

If you are really in trouble for gas multiply the usual 3:1 ratio by the pressure for the depth in bar but if you are pulling stunts like this get to 6m and go oxygen rebreather mode and pull some serious stops. Again if you are in that sort of trouble and diving with another rebreather his hoses will plug into your injectors - get inventive. Doing half an hour on a blob in a compromising position but getting back on the boat with no more problem than a blown oxygen first stage to pay for beats getting bent to hell and back.

As ever if you aren't checking the handsets a rebreather can kill you but if you watch the ppO2 it gives you time to solve a problem which OC never does.

nigelH