Rebreather "Round Up"

[Chuck_Northrup]

I understand your point on the OxyGauge, but have to disagree

More RB incidents resulting in fatalities have been linked to hypoxia than hypercapnia. The big difference is that during even a mild hypercapnia hit you "know something is wrong". As long as you acknowledge your body's warning signs and get "off the loop" you will be fine.

Hypoxia is a rather blissfull journey into the void. Granted if a diver is diving SCR 'according to Hoyle' the need for O2 analysis can be debated. Most Europeans dive without O2 analysis. The Azimuth does not have a ready-made port for O2 analysis and on the Dolphin and Ray it is seen as an "upgrade" not a standard feature.

On an SCR the situations which can lead to hypoxia include (as you know) running out of gas, blocked orifice, or improper gas use. The first two would have intrinsic warning signs (pressure gauge reading zero/excessive cycling of the ADV) and the third should not be done. ;D So if you don't want an OxyGauge fine, but for me it is nice for peace of mind.

Hypercapnia on the other hand can currently be detected only by "bio-feedback" so to speak. Other than exceeding the time limit (don't do it), or catastrophic scrubber failure (which would cause bubbles/increased resistance/etc), the remaining causes are those I listed earlier (poor packing/loose o-ring/using dead scrubber material) and NONE of these can be detected by modern CO2 "analyzers" in an RB. So you have the potential of a diver who "feels something is wrong" but checks his CO2-meter that says everything is hunky-dory and suffers an event. :'(

Mass spectrometry is the most reliable means of CO2 detection but is not possible in the humid environment of an RB loop. The need for a "robust" system which can handle the stress of a dive environment (bumpy boat ride/giant stride/etc) eliminates the use of most "surface" CO2 analyzers. :-\

The CO2 analyzer on the Evolution uses heat/moisture/and time to estimate "usable" scrubber time. The possible "false positives" related to this system make it unreliable in several instances. Like I said earlier, it makes ignoring common sense and proven protocal much to easy. :o

If and when a GOOD and RELIABLE CO2 monitor comes out I will be all for it. ;D

CN3