CCR Skills

This text is a supplement to your CCR training. We will review all of these procedures together, and all skills will be demoed by me. Reading about the skills beforehand is a great way to prepare for your class. CCR diving requires a lot of new concepts and procedures. Take notes and take the skills seriously!

Build Checklist

Why: The manufacturer’s build checklist is our guide to unit assembly and confidence-building. The build checklist will seem superfluous to guide your build after a few builds. That’s only one of its functions. The other function is to build confidence. You don’t want to be giant striding and think, “Is my boreplug in?” We have confidence the boreplug is in because we completed that step on a written (or app) checklist.

We have a few tests as part of the build

  1. Positive pressure check – tests loop integrity
  2. Negative Pressure check – tests loop integrity
  3. Oxygen leakdown check – tests O2 system integrity (pos/neg does not check anything with O2)
  4. Prebreathe – ensures solenoid and cells function.

We have no way, in any test, to test the scrubber, or ensure the build is done properly. That’s where the checklist comes in. It gives us the documented confidence of a good build.

Predive Checklist

Why: Use your buddy to double check critical components to build confidence.

Before we dive, run through a personal checklist. After you are ready to dive, check with your buddy. The point of the predive checklist is to see and hear confirmation that things have been done. This check is crucial and needs to be done every dive. The smoother it is, the less likely we are to skip it. 

Example

Valves and SPG – Show your buddy your O2 is on. Tell them your O2 pressure. They respond with the same actions. Watch them. Then, each of you watches the other touch the diluent valves and say the pressure of dil.

Reading the checklist and saying “yes” is about as practical as not doing the checklist.

Prejump checklist

Before we jump off the boat, or descend on a shore dive, we need to double check a few things. Just like when the divemaster makes sure your cylinder valve is on before you jump.

  1. Breathable loop 
  2. O2 is on
  3. Dil is on

Is the loop toxic? Will the CCR continue to deliver O2? Can I bailout and inflate my BCD? These are the crucial questions we validate before a descent.

Descent Procedure

As we descend, Po2 increases and volume decreases. We need to keep Po2 to a reasonable level, and make the volume comfortable. We have a few variables to deal with here and a few different options.

At the surface, before we descend, use oxygen for volume replacement and ensure Po2 is appropriate.

  • Deflate BCD and start the descent
  • Open the ADV
  • Bubble check with buddy
  • Manage descent speed with BCD – add small bursts of gas to keep an appropriate descent speed.
  • Press ADV diaphragm if volume isn’t sufficient
  • Turn ADV off at target depth (assuming you have minimum loop)

When we reach the target depth, or stabilize depth, it’s time to switch to high setpoint. We have 2 options here.

  1. Solenoid Second: Use the MAV to increase loop Po2 to ~high setpoint, vent as appropriate, then switch.
  2. Solenoid First: Switch to high setpoint, as the Po2 climbs, check minimum loop and vent as needed.

Both are appropriate options. Either way, we manage minimum loop the entire time. The wrong thing to do is switch to High SP and then lose buoyancy because the solenoid increased gas volume. If you have appropriate buoyancy, swap to High SP and feel positive buoyancy, think loop – not BCD.

If the descent is fast, like a hotdrop, deflate the BCD and focus on getting to ~10ft for the bubble check. Monitor your Po2 and dive buddy. When needed (typically 2-5 ft), open the ADV and continue the descent. If the bubble check is more than a few seconds, your ADV may decrease the Po2 to the point where the solenoid fires. In this case, get ahead of the solenoid so you can predict buoyancy.

If the descent is slow, like a sloping descent, use o2 until 20ft. This keeps the Po2 up, makes the solenoid irrelevant, and removes the ADV from the equation. Then, at approximately 20ft, engage the ADV and let it replace volume to the bottom. A fast descent will cause the PO2 to spike if we start high – think about the situation.

Anytime we stabilize depth, minimum loop, and buoyancy, the ADV needs to be turned off. 

Minimum Loop

Our goal, during every phase of the CCR dive, is to have a loop that has ideal volume. We call it minimum loop; it’s not a contest to see how negative we can have the loop, but it’s typically more common to have a positive loop than a negative one. 

We test for minimum loop during all phases of the dive. Take an unnaturally large breath. If you feel the lungs collapse during that breath, the loop is too low. If the lungs give a tiny bit of resistance at the final part of the breath, that’s typically the perfect amount. Some people go a bit more or less, but we shouldn’t have 2 lungs of gas inside the loop.

  • We want the perfect loop volume because it’s less volume to vent on ascent, easier to do flushes, and more comfortable breathing.
  • There should be no resistance in a normal breath cycle, normal breathing should be comfortable.

Ascent Procedure

As we ascend, the volume and FO2 remain fixed within the counter lungs. That will expand, and as pressure decreases, PO2 will decrease. That means we need to add O2 and vent volume during the ascent. 

Goal: Ascend at 33ft/min with a constant Po2 and minimum loop.

  1. Ensure min loop and ADV is off
  2. Start going up*
  3. Test minimum loop and vent**
  4. Watch the ascent rate, buddy, and vent BCD to control the ascent rate***
  5. At some point (typically 30ft) switch to low SP and go into manual mode. Keep Po2 at high SP.
  6. At 20ft, do an O2 flush and switch to O2 CCR mode

* Add a small burst to the BCD or back-kick up slightly. Let the BCD start to pull you slowly up. Do not go vertical and kick up.

** Take a huge breath in to see how much extra gas is in the unit.

*** While the loop is part of our buoyancy, think of the loop as the loop and the BCD as buoyancy.

Trim and kicking – We must be as still and flat as reasonably possible during the ascent. Flat makes the unit breathe easiest. Still makes it easy to see what’s going on around us. If we want to go vertical to look up (check our smb isn’t tangled, for example), don’t get tricked by the sudden feeling of positive loop pressure and make the look momentary.

  • Watch PO2
  • Watch buddy
  • Watch the ascent rate
  • Check loop volume
  • Pay attention to the environment

Bailout

Why:Any time we have an out of range problem, we’re uncomfortable, or we need sanity breaths, we should have quick and easy access to bailout gas. 

Goal: Get off the unit, get onto open circuit gas, and tell our computers what we’re doing.

  1. Close DSV
  2. Remove DSV and swap to necklace reg. 
  3. Swap controller and independent computer to BO mode.
  4. As you ascend, routinely vent the loop with the pull dump
  5. If you are bailed out and ascending, turn the oxygen cylinder off so the solenoid cannot fire and increase buoyancy.

Before we get back on the unit

  1. Check PO2
  2. Remove reg
  3. Insert DSV and clear
  4. Open DSV, add gas to min loop
  5. Switch to CC mode
  6. Switch to high setpoint

BO mode tells the computers we are no longer on the loop. This changes our decompression calculations, and switches the computer to Low SP.

  • Bailing out is always ok
  • Never leave the ADV on when you bailout
  • Always swap you computers and verify they’re set to the correct gas.
  • Always check your Po2 before you get back on the loop
  • Always swap back to CC mode and switch SP when you get back on the loop

Cell Validation at Depth (dil flush)

Why: We have lost confidence in our cells for some reason. Maybe one is reading low. By doing a cell validation, we introduce a known PO2 and see how the cells react. This is only appropriate for an in-range problem.

Goal: Replace the entire loop with diluent (known gas) to validate the cell readings.

  1. Check dilPO2 value on computer
  2. Switch to Low SP
  3. Vent loop to negative
  4. Open ADV and allow loop to fill to minimum loop volume
  5. Check Po2
  6. Repeat 3-4 up to 3 times

Details:

  • Check dilPO2 value on computer – Now we know the expected value. If this value is lower than our lowSP, we cannot do a proper cell validation. 
  • Switch to Low SP – so the solenoid doesn’t interfere
  • Vent loop to negative – get ride of the existing gas
  • Open ADV and allow loop to fill to minimum loop volume – fill with the known gas
  • Repeat 3-4 up to 3 times – Don’t expect a perfect flush the first time, 2-3 flushes might be needed.

A dil flush is not for rapidly reducing the loop PO2. If the loop Po2 is out-of-range-high (or low for that matter), we bail out. This is a cell validation. Using a dil flush on an out-of-range loop (aka a toxic loop) is not a good idea.

Cell Validation at <20ft (O2 flush)

Why: We have reached our safety stop. An o2 flush gives us a perfect minimum loop and tests our cells for current limiting. Obviously, this test doesn’t help for the dive we just did, but it gives us confidence for the next dive. 

Goal: Replace the entire loop with O2. We’d expect a spike of Po2 to a max of 1. And a quick decay.

  1. Vent loop to negative
  2. Press O2 MAV and allow loop to fill to minimum loop volume
  3. Look at PO2

We aren’t doing this to achieve a high deco Po2; we’re only aiming for a high Po2 during the flush. Our deco Po2 should be the same as our bottom Po2.

O2 metabolic drill

Why: This is a class drill to see the effects of PO2 loss.

Goal: Watch Po2 drop and see if volume or PO2 wins.

  1. Get a comfortable min loop and check time
  2. Switch to Low SP
  3. Swim at a static depth and watch PO2

End Drill if either of the following happens:

  • You need to use the ADV
  • Solenoid fires
  • You clear your mask or accidentally vent the loop (restart drill)

Semiclosed Rebreather (SCR) mode 

Why: This is a gas extension drill. If you ran out of O2 and had to travel horizontally, this allows you to use less gas than bailing out.  .

Goal: reduce gas loss by breathing the same breath a few times.

  1. Flush the loop with dil
  2. Breath the loop until the Po2 drops (3-5 breaths)
  3. Flush the loop with dil again to raise the PO2

This is never appropriate if we lost electronics – if you don’t know your PO2 you must bailout.

Mask Clear, Mask Remove, and Replace

Why: A CCR mask clear has a different effect than an OC mask clear. The fewer bubbles we let escape the mask, the less our loop is affected. 

Goal: Reduce the amount of bubbles we let out during the clear and prepare for the change in loop volume.

  • If we expect a large amount of loop volume loss, open the ADV before you clear.
  • Reduce the amount of gas loss with a bubble-less mask clear. Slowly exhale through your nose into the mask and reduce the water level in small increments. Think more about filling the mask with air than pushing the water out of the mask.