How do I dive within a mixed UTD/DIR team? (OC and mCCR)

Recently there has been a lot of discussion about how a UTD/DIR diver might deal with a mixed team of rebreather divers - either pSCR or now mCCR - and open circuit divers on the same team or dive operation. So, I thought I would put together a little blog outlining some of the things to consider while bringing in some of my now over 10 years of diving a rebreather in a DIR/UTD configuration, many times on a mixed team.

Sure, in the late 90's it was the first Halcyon pSCR Rebreather, which we affectionately termed "the fridge,” and then later, around 2001, we started using the pSCR - RB80. Now, almost 8 years later, we have moved to fully closed circuit systems or mCCR (manual closed circuit rebreather) which we call the MC90 when using the copis and the new MX90 without copis.

But regardless of which unit we dive, we have stuck to the core principles of UTD/DIR - consistency within the team (and community) of bailout volume and logistics, standardized gases for bottom gas and deco, Ratio Decompression strategies, matched equipment configuration, skill procedures for out-of-gas and valve failures, and so on.

The rebreathers (pscr's, and the mccr - mc/mx configurations) are simply a classic DIR/UTD technical configuration (a set of doubles and deco bottles as needed) wrapped around the rebreather which syphons off a tiny amount of the OC gas for use in the CCR but leaves the majority of the OC gas for bailout. Keep in mind that both the pSCR and the mCCR add gas (either O2 or Dil) manually - there is nothing on the system that adds any gas without you wanting to. Meaning there is no solenoid or ADV (auto diluent valve) system, no electronics or other things that could unintentionally add gas without your knowledge. It is simply a CO2 canister, counter lung, breather loop and so on with O2 sensors to measure the PPO2. As a side note: UTD does require an O2 sensor on all rebreather configurations including any pSCR system such as the RB80 or RB2000 and others.

So here are a few things that are important for an OC buddy when diving in the mixed team with pscr and/mccr diver. These apply specifically when diving with a diver using the MC or MX fully closed systems :

1. It's important that a RB diver is always moving around slightly so you know they are alive, as there won't be bubbles to confirm breathing.

2. In emergencies, such as CO2 hits, valve failures or out of gas situations, the RB diver immediately bails out from the CC to OC by simply flipping the BOV to open circuit. This happens by moving the lever on the bailout valve to the down position, which opens the "necklace" regulator on the bail out valve (BOV). Now the bailed out RB diver is on the backup reg on the left post, just like a standard set of doubles, and both divers in a mixed team are on open circuit. The backgas is a UTD standard gas and is always breathable at any point in the dive. This bailout procedure eliminates the need for the CC diver to monitor the rebreather while dealing with the emergency. The CC diver can now give full and undivided attention to the emergency. As we carry ample bailout this is not considered problematic from a gas management perspective and because the bailout valve is simple and easy to access it and will be easy to return to CC once the emergency is dealt with. We propagate the message of "when in doubt, bailout."

A side tangent : The message propagated in other circles of the ccr diving world of staying on the rebreather at all costs while dealing with an emergency is massively problematic, as the CC diver can potentially stop monitoring the rebreather while dealing with the emergency and therefore may create a very dangerous situation. Even if the electronics are only there as a backup they too could fail as they are not in use at all times.

The reason this message of staying on the CC while dealing with emergencies was propagated is because number one, many ccr divers do not personally carry sufficient bailout volumes to handle an emergency in OC mode (they try to divide the bailout for one person between team members or just simply go alpinistic style - no bailout at all) and secondly because their bailout configuration is so massively convoluted and/or difficult to donate or restore to it's original state that once deployed and the emergency is dealt with, returning to CC can be a massive pain the butt, so they simply just try to stay on the unit while dealing with the emergency.

An example I have seen is carrying the bailout in a stage bottle which forces one to select a bottle, pull the regulator from the stage bottle bungee, remember to turn it on and then bailout to deal with the emergency, then once dealt with try to return the regulator to it's original position. It reminds me of the "pre" DIR days when we would stuff the long hose into a bungee and would have to pull it out of the bungee to donate, then it was such a hassle to return to the bungee. So we would not bother practicing s-drills because it was too much trouble to put the long hose away. Hence the Hogarthian system was born to simply wrap the long hose back around your neck, which has now become the standard method of UTD/DIR long hose configuration.

But, back to mixed teams:

3. If an OC teammate needs gas, the CC diver switches to OC by moving the lever on the bail out valve, unclips the long hose, lifts the loop out of the way, donates the long hose, and stays on OPEN CIRCUIT. Now both divers are on OC, problems can be sorted out, then the RB diver can go back to CC. We put the CC diver on open circuit during an emergency so there is no need to manage the rebreather and the PPO2.

4. If an OOG diver grabs the regulator off the O2 bottle in an emergency, the regulator has an isolator at the second stage, so essentially the gun is not loaded - although the bottle is on and feeding the RB, the second stage is off, so it takes two steps to breathe pure O2. There's an over pressure relief valve on the O2 first stage so the second stage can be isolated safely. At recreational depths, there often won't be a second stage on the O2 bottle, since the only time it would be used is for emergency O2 deco.

5. Cautions that OC divers in a mixed team should know about:

Prevent the system from flooding by not taking the loop out of the mouth unless the BOV is set for open circuit.

Floods make the rig heavy, but the wing should provide enough lift to bring the diver to the surface in neutral buoyancy. A small amount of water in the loop can easily be cleared.

PPO2: There are two handsets and a head-up display. The handsets are clipped to the hip d-rings of the diver, again in the DIR/UTD thought process, right primary and left backup. The units are always monitoring the PPO2, however the display may turn off in power save mode - pressing any button on the handset will turn on the display. Both handsets display the individual PPO2's from each of the three sensors on the main screen. Each handset is independent of the other so if the primary or secondary were to fail you would have the other.

The head up display, or HUD, is connected to the primary handset so the diver can conveniently read the PPO2, since the displays are clipped to the hip d-rings. The HUD simply flashes an LED light with three different colors. green good, red not so good and amber almost good :). They flash a sequence for each sensor (so a cycle of three sets of flashes). So for the PPO2 of 1.0 is one amber flash per sensor - flash-pause-flash-pause-flash-pause, then a longish paused between the set. There is one additional flash of green light for every tenth higher, and one additional flash of red lights for every tenth lower.

So PPO2 of 1.2 is two green flashes, two green flashes, two green flashes, pause, then two green flashes, etc.

PPO2 of .7 is three red flashes, three red, three red, pause, etc.

PPO2 of .5 or less is constant red flashing.

PPO2 of 1.5 or higher is constant green flashing.

6. Injector failures:

Dil injector sticks open...isolate the injector using the omni swivel isolator at the injector hose...this stops the flow of dil into the unit but leaves the right post open to donate. If isolated, dil gets added to the system by taking a breath from OC and blowing it into the loop.

O2 injector sticks open...shut down the O2 bottle. Feather the valve to inject O2 or plug O2 into the diluent side, isolate diluent as above and use Diluent injector to add O2 to the system while using above method of cc to oc to add dil when needed.

That's about it. There is no solenoid to fail, no ADV to fail, three O2 sensors all working in parallel...it's actually pretty simple.

Anyways, I sincerely hope this helps many of you understand how to integrate divers who are taking advantage of the upcoming ccr technology into their diving and your team. In summary, remember the overriding concept with a mixed team is that in any emergency or odd situation, the CC diver goes immediately to open circuit, putting both divers in the familiar position of diving standard DIR/UTD configuration doubles.

Safe diving
AG