Diver one of sixteen to die using high-tech gear

[DiverMole]

This is going to be a long reply (in several pieces as there may be a max message length) to address many of the misunderstandings and bad information in this thread

I will use the Inspiration as the example as thats the unit I'm most familiar with, but this applies to almost all other CCR's

On the Inspiration when you exhale the gas goes to the right counter lung/ water trap, it then flows over your shoulder into the base of the CO2 scrubber where it is warmed and cleaned of CO2, there is a water thrap at the base of this to. The gas then goes into the mixing head where O2 is injected if needed. It then flows past triple redundant O2 cells and up to the left counter lung/water trap and to the mouthpiece

The Sensors HAVE to be in the breathing loop as thats what you want to measure. They also HAVE to be between the injection point an the divers lungs as you want to measure what you are going to breath, not what you exhale

The 3 sensors HAVE Hyrophobic (teflon) membranes fitted, Water positively runs off of them, They are all at 90 degreeas to each other so it is impossible for water drops to land on all 3 at the same time. Water on the sensors of the Inspiration is NOT an issue at all (there were some early problems with non hydrophobic cells). Cendensation does occur in the head area (fresh water) but not on the cell face (mainly on the cold metal fixings)

The cells are monitored by the handsets (double redundant with instant failover) and use a voting logic system, where the nearest reading 2 cells are averaged. Alarm conditions arise in the following situations

1) Any cell deviates more than .1 bar from another
2) The reading is deemed to be below .4 bar
3) The reading is deemed to be above 1.6 bar
4) Any cell fails to produce output
5) Battery Low (double redundant)

The alarm is VERY loud and gets louder at depth (its painfully loud below 40m) and is sounded as part of the initialisation routine to verify its use, Its also flashed on the handsets

The cells are calibrated in the machine. The calibration routine requires the user to enter the ambient pressure, the % O2 in the O2 bottle (not always 100%) and to open the mouthpiece. The unit then constantly injects O2 and watches the cells readings rise. When all 3 cells are stabilised and as high as they go these are calibrated to the %O2 you entered. Sensible divers do an O2 flush at 4m to veryfy 1.4 bar is reached before diving (normal dive PO2 is 1.3 so this proves the cells are able to reach the needed values)

There is a good predive routine to follow that checks the loop integrity (both positive and negative) and the function of all mechanicals. You also prebreath the scrubber to activate it and to check for CO2 bypass

I and many others also fit a VR3 with a 4th O2 cell as a separate and independant monitor. This can be calibrated in air or O2 or in the unit.

During the dive you are not task loaded at all and you check your handsets as often as you should be checking your deco computer and SPG on a normal dive. NOTHING EVER HAPPENS FAST ON A REBREATHER!!, even if the O2 failed you would have 2-3 mins to notice and fix and the alarms would also remind you if you failed to look at the guages. Fastest failure is O2 solenoid jammed open. You can hear this and feel the excess bouyancy immediately as well as the alarm would sound

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