What does the future hold for rebreathers?

[iain/hsm]

Originally Posted by nigelH

I have yet to be convinced that a CO2 sensor, accurate or just approximate will make a bit of difference to the accident rate.

I am seeing temp-stick users running scrubbers longer 'because they can' so, although I like mine, I'm not convinced even that was a step forward. You have to sort your scrubber requirements out before you get in the water. Anything that works later than that is just telling you you messed up.

Hi Nigel.

I recall we last spoke about this some three years ago, almost to the day on RBW At the time Rob Davie made positive comments, You I recall were still yet to be convinced. Sadly I guess he for one would have benefited.

Three years ago the accuarcy for our C02 detector then was 0.2% with a resolution of 0.01% with a 5 second responce time enough for a breath by breath analysis.

Well within the C02 maximum limit allowed of 0.5%

Let hope in the future C02 detectors will be fitted and while I may not convince all and everyone, just one would have been worth it. Regards Iain.

[iain/hsm]

Originally Posted by NotDeadYet

You have to wonder if CO2 has reached a level that a sensor can detect, will it be too late?

Not Dead Yet.

Quite the contrary as I stated above even three years ago we could detect first breath C02 analysis. So much so that the first few breaths you take into and through any model or make of rebreather you can "see" an initial "C02 Spike" This is due to the time needed for the soda lime to react, This spike lasts for about one to three minutes depending on the rebreather make or model and the type of soda lime used.

Then as the lime "kicks in" and absorbs the exhaled C02 the C02 level monitor will drop and the HUB alarm red LED light goes off to green. This is confirmation analysis of operation of both the system and the soda lime.

During the "normal" dive the detector will also show any high peaks high work loads, mushroom valve flapper failure or leak back, tracking, channelling even detect poor performing lime premature breakthrough and is also a method to validate different performing scubber materials and scrubbers etc.

Further more at the end of the dive, or say the last 20 minutes of the soda limes active life, the detector will also show an increase in C02. This is not quite the same a breakthrough C02 as some (military) rebreather models have a small tiny "background" C02 level throughout the whole dive.

So in answer it is not "too late detection" but informs you a specific level of C02 at detection levels you are simply not aware of. Iain Middlebrook.

[Janos]

Originally Posted by Drmike

both.

dont forget as your descending the adv fires in dil which dilutes the ppo2

Hi Mike,

I agree with everything apart from this!

Let's say you're on the surface with a loop volume of 10 litres of pure O2. ppO2 is 1.0

You descend to 10m (2 bar) and so add 10l of air (say) through your ADV.

The loop now has 10l of O2, and 10l of air.

fraction of O2 = (10 litres * 100% + 10 litres * 21%) / 20 litres
= (10 + 2.1) / 20
= 60.5%

But ppO2 = 60.5% * 2 bar (remember we are 10m)
= 1.21

Basically, for each 10m you descend, you add the %O2 to your ppO2. The ppO2 at 20m will be 1.42.

Janos

[Drmike]

Originally Posted by iain/hsm

I recall we last spoke about this some three years ago, almost to the day on RBW At the time Rob Davie made positive comments, You I recall were still yet to be convinced. Sadly I guess he for one would have benefited.

no he wouldnt have.

his death had bugger all to do with CO2.