Pre-breathing procedure

[Wibble]

Very unit dependent.

For the Revo, I use this process -- adapted from many stupid failures!

• Fins on
• Facing unit: turn on drysuit inflate, ensure hose is routed correctly (not behind you)
• Facing unit: turn on Dil, suck the loop and prove the ADV injects (not breathing from the loop, especially if hypoxic)
• Untie the box, climb in, strap tight, connect hoses and heater
• Check hoses and cables aren't tangled; tuck torch cable into waistband
• Check drysuit dump open and inflate; BCD inflate (small puff)
• Pull on Petrel, turn on -- solenoid should click (if it's quiet on the boat)
• Loop over head and in mouth, turn on Nerd,
• Fully turn on O2, should hear it injecting
• Breathe in, out through nose as O2 flushes through; check O2's rising (only one breath normally)
• Once over 0.7, keep breathing for a few breaths; remove loop.
• Finish donning bailout stages (already checked they work); turn on bottom bailout; power up and turn off other bailout deco stages
• Gloves on, mask spat in, etc.
• Check the BOV works (connected to offboard) - be careful if hypoxic.
• Breathe from unit until RMS (Revo Monitoring System / temp stick) shows there's more than 45 mins of scrubber, generally takes a couple of mins. This validates the scrubbers are in, have fresh scrubber, are scrubbing enough to warm up, etc.

Then:

• If a few mins delay <20mins do not turn off O2.
• If a long delay, >20mins (e.g. tide's still running, shot's dropped off the wreck)
  • Turn off computers, loop over the head
  • Turn off O2 (Revo has a leaky valve/orifice)
  • If the Petrel's off, this means you must pre-breathe again, i.e. turn the O2 back on.
• Before jump (literally at gate):
  • Check drysuit dump is open; inject gas into drysuit -- have drysuit (proves inflate is on)
  • Inject into wing -- have buoyancy (proves diluent is on)
  • Manually inject O2 -- can breathe (also proves O2 is on)
  • Check PPO2; last check of RMS/scrubber duration (should now be well over an hour)
  • Check: fins, mask on face, drygloves on and sealed.
• Jump.

 

[DS79]

If a few mins delay <20mins do not turn off O2.

• If a long delay, >20mins (e.g. tide's still running, shot's dropped off the wreck)
  • Turn off computers, loop over the head
  • Turn off O2 (Revo has a leaky valve/orifice)

Diving my rEvo, I changed the procedure and close O2 every time until just before I jump into the water (usually it takes us quite some time from doing the pre-jump check on the car until I walked to the water and waited for my buddy;-)).
The reason why I do this is not (primarily) to save O2 - I feel, to minimize my margin of error, I should do it ALWAYS the same way and not dependent on the circumstances (time to jump/descent). By always closing it, I have memorized it as one single procedure: hand on o2 valve and open/check p2 values-injection / go into the loop. In other words: I will not go into the loop without biefly having my hand at the O2 valve.

The pre-breathing, I do exactly according to rEvo's check list (RMS 0:45), which is usually perfectly matching a short walk from the set-up place to the water.

 

[bletso]

uhm, I do a pre-breathe to ascertain if my oxygen injection system is functioning correctly. It's not to check scrubber functioning, i keep track of scrubber material/dive time. A couple minutes above water may not be enough to see enough CO2 build up, but a couple minutes of O2 injection not working and monitoring your PO2 will definitely show up.