Quote: (Originally Posted by
silent running)
Hi Alex, thanks very much for all the good data to chew on. But I've got a few questions:
Can you explain this bit above about the OTC CLs and the "suprasternal notch" and EN 14143 depth measurements being eliminated with OTS CLs?
EN14143 measures hydrostatic pressure relative to the suprasternal notch (a point on your skin where your two top ribs join in the middle). This is wrong.
NORSOK U101, on which a lot of EN14143 is based, uses the correct measurement: hydrostatic pressure is measured relative to the lung centroid.
The result is that EN14143 is highly biased towards OTS CLs, for no valid reason. It also is highly penalising for BMCLs. With a hydrostatic measurement relative to the suprasternal notch, the centroid of an OTS CL can be the suprasternal notch, so there is no WOB penalty from diver position. In reality, OTS CLs do have a WOB penalty because their centroid is not the lung centroid.
Quote: (Originally Posted by
silent running)
Do you know how mbars compare to kPA units? I'm not even sure what kPA are, joules maybe?
There are conversion tools on the web.
Pascals are pressure. Joules are energy. mbars are pressure. ATM is 1.013 bars. PPO2 for example should be in Pa or ATM, but often quoted in bars without correcting for the difference.
Quote: (Originally Posted by
silent running)
And you mention in your test that you had 80% humidity in the canister/breathing machine. But isn't the humudity in a CCR loop very close to 100% and wouldn't this have the effect of increasing the WOB and thus effect measured resistive loads and is it necessarilly a linear increase for both EAC and granular as humidity increases?
It is not 100% because there is condensation in the counterlungs etc, and adding gas, even O2, dries the atmosphere because O2 has no water in it.
Quote: (Originally Posted by
silent running)
And while I understand the care taken in your study to islolate the various factors in WOB and the modular nature of the test protocol, I can't help but wonder if you really could just change the maths and plug in a radial. If I'm understanding the basic factors/maths, we would need to know the length of the grain boundry, the overall volume of the scrubber and then factor in the gas flow path, which will be dependent on the proportions. Doesn't seem so simple to me.
I just posted an answer to Dr Mike on the same topic. Using the method described is a very good first approximation (i.e. to within 10% of the right number). Measuring it has an error also (around 10% when all is done, due to differences in temperature, humidity, hose routing, hose diameter, turbulence at the base of the scrubber etc).
Quote: (Originally Posted by
silent running)
And back to Tim's 4 cent analogy, if a same sized radial starts out with a lower WOB to begin with, is that 4 fold increase in WOB due to moisture really that noticeable?
No, it is not noticeable. It just kills you.
That is the nub of the issue. WOB is not measured at all well by human lungs. The first thing the diver knows is when they start to get a CO2 hit. That can be too late.
Quote: (Originally Posted by
silent running)
EACs look like an attractive alternative to a conventional axial for several reasons, including your findings above relating to the stable WOB throughout the duration. But I doubt that an EAC which takes up the same volume as a properly propotioned, well insulated radial could match it's duration. Then we have the sorb vs. EAC portability issue, the final deal breaker for me... -Andy
See earlier I posted figures showing over 5 hours from an EAC under EN14143 conditions. That would be quite a challenge for any granular system.
Cheers,
Alex