Even if recent tests revealed that our concerns have been dealt with adequately, it would not change the paper at all. If you read my post again more carefully, the simple study we conducted was a response to comments made by Alex on line almost 2 years ago.
G'Day Simon, No worries. I presume the fact that your results were based of information published on an online forum 2 years ago rather then testing of the actual product was made clear in the report and your presentations.
Having said that, I would be only too happy to publish favourable results in a second paper if given the opportunity to test the actual unit (see below).
So you have published and presented unfavourable results based on speculation about the actual performance of the DL design then?
Seems that while your paper was peer reviewed and appropriately scientific you have stated the performance of say a SAAB car by testing a FORD which seems fishy....
That brings me to your claim that CO2 detection in the APOC has been tested to the standards you quote. That is all well and good if that testing addresses the potential inaccuracy we highlighted.
You said it needed to be independently tested, I simply pointed out it already had been to what appears to be a very rigorous level.
So here is a simple question Brad, and all it requires is a simple categorical yes, no, or don't know:
Has CO2 been measured using human subjects and properly calibrated analysers deployed simultaneously at the mouth and pod (end of hose) with the latter compared to the APOC pod reading over a range of tidal volumes from 500ml to 2000ml?
Properly calibrated analysers would be a yes as they include calibration details for their mass spec in their reports, pg 19 in the below one.
Don't 'know' on rest..., but from the following I would guess yes.
As report on Fault_Study_CO2_Bypass_110105
- Breath by breath measurement of CO2 was done
- They used zero end of inhale CO2 at the mouth to confirm that the flapper fault wasn't present.
- In EN 14143:2003 it stipulates that the Volume Weighted Average CO2 be measured during the scrubber endurance test at the mouth. So ALL testing of the iCCR would mean that they are measuring the CO2 simultaneously at the mouth and pod...
- The Notified Body required the VWAI CO2 measurements to be taken at each point of the dive, including at the start of the dive, to ensure the end-of-inhale contained zero CO2.
- Apparently measuring end-of-inhale CO2 prior to the inhale one-way valve gives false scrubber endurance and VWAI CO2 results in many rebreather designs when this fault condition occurs.
- They advise that in practice the low tidal volume alarm is not triggered, because if the diver does not metabolise enough oxygen, then the PPO2 in the rebreather will rise in all Deep Life O.R. designs (all use orifices to control flow), causing an oxygen warning, then alarm: this occurs well before the tidal volume drops anywhere near 300ml. This high PPO2 occurs in the iCCR at a tidal volume of less than 1 litre per minute with a RR of 14. Which appears to indicate that for 1/3 of the range your worried about the diver may well be on OC.
- During manned dive testing, the CO2 alarms were triggered in the following circumstances:
1. Before starting a weld, the diver would hold his breath, causing the first exhale to have a high CO2 level, tripping the alarm. This false alarm source was removed by increasing the averaging period.
2. Divers talking for long periods using intercoms, would reduce their tidal volume, which increased the calculated end of tidal CO2.
3. Some flapper valve combination's caused the CO2 warning to trigger.
- The gas fraction was measured in the following seven points of the breathing loop. 1. Mouth (MOUTH)
2. Exhale channel immediately downstream of the exhale one-way valve (EXH) 3. Centre of the exhale counterlung (EXH_CL)
4. Inside the base board bell membrane immediately prior to the scrubber (SCRB in)
5. Scrubber output tube (SCRB out)
6. Centre of Inhale counterlung (INH_CL)
7. Inhale channel immediately upstream of the inhale one-way valve (INH)
- Errors in the phase delay compensation would cause fundamental errors in determining Volume Weighted Average Inspired (VWAI) CO2, and in assessing the Deep Life CO2 sensor: the CO2 Lissajou figure would be incorrect. To eliminate this source of error, the phase delay at each measurement point was calibrated.
- The Deep Life CO2 monitor measures the same average CO2 as that measured by the mass spectrometer just upstream of the scrubber, but displays 7.0 % SEV when the consumption of 1.78lpm is simulated: this is correct. The actual RMV is 40lpm, with a 20 bpm RR, but the oxygen metabolised is 1.78lpm STPD at 1.6lpm, so the calculation used by the CO2 monitor concludes the RMV is 49lpm, and the tidal volume is 2.45 litres. Applying these numbers to the formula described for determining the peak CO2 in the previous section of this report, results in 7.0 % SEV of CO2, and the actual number measured using the mass spectrometer is 6.9% SEV.
Why, you apparently have a lab with mass spec and capability to conduct testing of CO2 sensors in rebreathers designed for underwater use to a suitable standard proving that the DL design doesn't work without even testing it!
In addition, I will once more in public repeat my offer to conduct this testing with you present, and my promise to publish the results be they favourable or unfavourable to the APOC. I would like them to be favourable, because we all want to see this system work. All you need to do is provide me with a moutpiece, hose and CO2 pod. What could be fairer than that?
Noted.
Out of curiosity, did you notice the same flapper valve fault that DL have reported in your testing?
What depth did you do the testing for your paper too?
In any event, the key point is this: DOES IT WORK? So far, I have not seen any data that addresses this question, and as mentioned above, I doubt that the testing Brad quotes addressed the issue. And the second key point is: IT WOULD BE EASY TO DEMONSTRATE WHETHER IT WORKS OR NOT, AND I HAVE OFFERED TO DO IT FOR THEM. Any controversy around this issue could be made to go away in a weekend's work for me, yet I have not been taken up on this offer. It makes me slightly suspicious.
Simply out of curiosity what is your test setup and how does it compare with what DL have published they used?
What would your testing give DL considering the only controversy seems to be generated by you et al?
Agreed, and we said that in the paper. I reiterate that the paper was a response to an obfuscation of the fact that low tidal volume breathing could become problematic at some level of breath size. Having said that, and as we point out in the paper, tidal volumes around 500ml could become relevant in some situations in diving.
What has the response been from the committees that draft the CE and NORSOK standards as well as the likes of NEDU to this information?
However, there are significant and (to date) unresolved concerns about the way they are going about it.
Rather then saying, interesting wonder how they did it and ordering one to trial, you seem to be saying it can't be done, but
it can be if I am consulted....
I thus get very annoyed when Brad trumpets their R&D as beyond criticism without acknowledging the substantial debate that has surrounded this particular issue. Even worse is his quoting of testing to specific standards which probably don't even address these concerns as some sort of proof that the issue doesn't exist.
Simon, I still have yet to see any testing proving that the DL engineering doesn't work as intended. I seriously would like to see valid criticism of DLs R&D with calibrated test results of the ACTUAL product in question backing up the criticism. Also other manufacturers and interested parties like yourself publishing testing of rebreather designs to the same level so folk have a choice....
Am still sourcing a copy of your complete paper, though I understand from your talk, what you have pointed out is that end of tidal CO2 is not related to the mean CO2, when one does not measure tidal volume.
Kind regards
Brad