scr bailout from mccr

robertfondren

Assuming depth of 40 meters, diluent 21% O2(air), do I not have roughly 20 breaths on the loop before venting and manually refilling my inhalation bag? Assume my electronics have failed and I have no means to measure loop po2. Again this is assuming I'm in bailout mode with no means to introduce pure O2 to the loop. If I were on the surface, the ratio would obviously be 4 breaths to every vent, so @ 5atm, I should have 20 breaths right?

JonORunde

Are you thinking "I dont need that much O2 when I am deep" ?

That is a very bad idea.

i am guessing that when you bailout, you would want to come back up reasonably quick?

You would then want to have enough O2 in your loop to be able to breath it all the way to the surface methinks...

Jon O

lizardland

Every now and again I do a whole dive on manual SCR so I can see how my PO2 reacts and what works for me (I spent a dive on sunday doing it). I'd suggest doing the same while your Rebreather is functioning properly and you can see what is happening rather than waiting until you need it. I tend to go for quite a frequent dump ratio as it is less demanding on brain power, I've got plenty of OC bailout so I don't have to be too miserly with gas use and I like to know that my loop is still happy without any displays.

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sddiver

20 breaths? How did you come up with that number? Your going to go hypoxic, especially as you ascend. Granted your set point starting is probably 1.3 but were assuming you lost your sensors and you don't know your loop po2, and your po2 are dropping as you ascend. 1.3 from 5 atm turns into .26 to the surface assuming no o2 is consumed. Now take 20 breaths off that loop, I would say it all will end badly. Talk to your instructor about what he recommends.

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Muddweller

For me I use 5 breaths then dump, suck some dill in then repeat until at 6m. Then switch cmf valve back, dump and inject pure o2 until surface. This I have drawn from my own experimenting on the surface and simulating having to go SCR for a ppo2 monitor failure.

Even during a fairly hard swim my ppo2 never dropped below 0.17, and since in a real situation I would be on o2 at 6m its not really an issue (unless I forget of course )

I had a battery failure once and had to use the procedure for real, it was a bit scary but you've just gotta trust the physics or bail OC.

If your on mccr why do you not have facility to inject 100% at 6m ?

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viscya

This is the sort of question that will be answered by your Mod-1 class. I suggest you ask your instructor.

If you are at minimum loop volume at the surface, then each breath will drop the PPO2 by 3-4 percent. You can go hypoxic very quickly. I don't believe anyone recommends SCR above 30ft.

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RonMicjan

What you need to do is practice while you have working displays and document what happens. The number of breaths available to a diver is dependent on many things, diluent O2 %, metabolism of diver, depth, volume of entire loop, how much you drag in when you do hit the dil for fresh gas. Of course it will change with ascending but you dont want too many different variables to remember. 5 breaths and exhale one in SCR to 20fsw/6M and flush with O2 is a good strategy, unless you have seriously hypoxic diluent, but then, you will have deco obligations and should be on a full OC bailout plan then anyway. I teach SCR for a horizontal swim, then OC or open loop bailout to the surface with safety stop and O2 flush (if you are still on the loop) at 20fsw. No worries on the ascent that way.

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robertfondren

Allright, full disclosure. What i've done is taken an ida72d2, replaced the dsv with one from an ida59, removed the O2 injection system, and replaced this with a normal second stage with the exhaust ports blocked. At this juncture, the only gas I have available is air. What I believe it is capable of doing is: 1. Giving me 4 breaths to each vent at the surface, 2.Giving me twenty breaths per vent at 132 feet. I have no means of monitoring the pO2 YET! The second I have my scrubber filled properly, I intend to test these beliefs. I will not be alone, and if a Mod1 class for converted ida72d2' s were offered, I would of course be the first in line. Now that my dirty little secret is out, is anybody still willing to talk to me, or have we already reserved a space in the memorials? LOL

Simon A

Now you've described what you've built, my first question is do you have any PPO2 monitoring system? If not then what you've planned to do could be very risky.
If you do have PPO2 monitoring then it's possible to run an SCR on air, but you realy want to use open circuit when you get shallow for both ascent and descent, (I personaly wouldn't try it above 30 feet).
Also you need to be aware that if you run the unit scr on air, you are racking up deco comitment even faster than you would if you were diving air on open circuit.
Stay safe
Simon A

denzel

Robert,

I have some 3 display ppo2 monitoring for sale.
PM me if interested.

denz.

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