Diver one of sixteen to die using high-tech gear

[DRE]

Divermole: "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"

"Fine, then I'll keep my replies focused on the Buddy as it comes from the factory - there are plenty of aftermarket options available for the unit, all trying to fix inherent problems idiomatic to the unit. I honestly believe that if you have to resort to an array of aftermarket options to make a $6000 piece of kit safer it already is a moot point. Funny thing, I don't need anything aftermarket for my tanks, regs and backplate..."

Divermole: "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)"


"There is a small metal screw inside the oxygen sensor compartment, it is located directly across from sensor number two. Condensation often forms on this metal screw and will allow droplets to fall onto the oxygen sensors. This will happen particularly if the diver moves from side to side as in dumping gas from a drysuit or if they invert from horizontal for any reason.
Condensation is inherently found within this area and will form on the oxygen sensors even without this metal catalyst. The O2 sensors are located on the inhalation side of the breathing loop, so you have warm gas that just went through the scrubbing process meeting with cooler gas that you will inhale thus the condensation forming on the cell faces. This condensation causes discrepancies/inaccuracies within the cell readings and they begin to VOTE trying to figure out which one is more than .2 bar out of line with the other. Cell warnings will manifest within this period of time and the diver will begin to get audible and visual alarms ...task loading increases."


Divermole: "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 unit alarms if it senses a PO2 over 1.6, which is a good thing. Problem with this is that many of the divers will run 100% oxygen at 20 ft which is a PO2 of 1.6, if they drop below the 20 ft they get an alarm, fair enough. If you have several Inspiration divers in close proximity with cell warning alarms, and high PO2 alarms it becomes very difficult to know if the alarm is coming from your unit or from another diver. Some will be able to assimilate this to being in an area where several cellular phones begin to ring and everyone pulls out their phone to see if it was theirs. Mix this with CCR divers using wrist computers that alarm and you really have an orchestra playing down there, so much for the peace and tranquility of "no bubbles".


Divermole: "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"

"As the diver descends they must equalize the counter lungs, if this procedure is not adhered to and they begin an uncontrolled descent the lungs collapse and the diver is not able to breath, an automatic diluent add is an aftermarket product which does combat this. But since we are talking factory here the diver is faced with equalizing counter lungs, ears, sinuses, mask drysuit, BCD, monitoring PO2 on handsets, buddy position (as far as they dive with buddies), light and depth in the water column. Seems to me like this might be a busy time in which things could move very fast, especially when going wrong."