CCR diving

What it is

The Deco Planner can plan a Closed Circuit Rebreather (CCR) dive instead of an Open Circuit (OC) one. On a rebreather you do not breathe a fixed gas. The unit holds the loop at a target oxygen partial pressure (a setpoint, in bar) by metering in pure oxygen and diluting it with a diluent gas. The planner models this loop, builds the decompression schedule from it, and works out how much oxygen and diluent the dive needs. It also models an Open Circuit bailout so you can see your escape schedule if you have to come off the loop.

This page assumes you already know how to build a basic plan. Read Deco Planner first for gases, levels, gradient factors, and reading the results.

Enable CCR

There is no separate “CCR mode” switch. CCR lives in its own section in the plan editor, between the Dive Profile and the gas list. The section is titled CCR and starts collapsed with a Disabled tag.

To go back to an OC plan, expand the CCR section and tap Remove CCR. This is confirmed, and it is not destructive: your rig is kept as a snapshot, so if you enable CCR again on the same plan you get your edits back rather than the defaults.

The CCR Rig

The CCR section shows two tappable cards. CCR Gases holds everything you carry; Setpoints holds the loop PPO₂ targets. Tapping a card opens a focused edit sheet. Edits save when you dismiss the sheet (swipe down, tap the backdrop, or the header tick).

Diluent and cylinders

In the CCR Gases sheet you set:

Field	Meaning	Notes
Diluent O₂ %	Oxygen fraction of the diluent	21 % is air; drop it for deeper dives
Diluent He %	Helium fraction of the diluent	For trimix diluent; 0 % for air or nitrox
Diluent cylinder	The onboard diluent cylinder (volume and pressure)	Drives the diluent-required estimate
O₂ cylinder	The onboard pure-oxygen cylinder (volume and pressure)	The unit meters this into the loop
Loop volume	Total breathing-loop volume (counterlungs, hoses, scrubber)	Default 6 L; drives the diluent compression estimate on descent

The sheet shows a live MOD (maximum operating depth) for your diluent at your deco setpoint. The hypoxic warning shows one level up, on the CCR Gases summary card: a too-lean diluent (one whose oxygen content gives an unsafe PPO₂ at the surface) gets a red critical badge that prints the surface PPO₂, so you catch it before you open the sheet to dive it.

Diluent switches (dilout)

The rig carries exactly one onboard diluent. To switch diluent during the ascent you do not configure a second onboard bottle. Instead, the Setpoints sheet has a Diluent switches list: each entry says “at this depth and shallower, breathe one of my Open Circuit bailout cylinders through the loop”. Divers call a bailout bottle used this way a dilout (the formal term is offboard diluent), because the same cylinder serves both roles.

By default the list is empty and the whole dive runs on the onboard diluent. That is the right setup for most CCR dives. Adding a switch is a deliberate, advanced choice, and there are three real reasons to make it:

1. Shorter deco on deep trimix dives. At a fixed setpoint, the inert content of your loop follows the diluent. Switching from a helium-rich bottom diluent (say 10/70) to a leaner mix (say 18/30) at 30 m steepens the helium gradient out of your tissues, the closed-circuit cousin of an Open Circuit deco-gas switch. Practitioners report meaningful savings on long trimix decompressions; the evidence is debated, but the practice is established and the major planners and computers support it (see Sources).
2. Safe diluent flushes at shallow stops. A 10/70 diluent at 6 m gives a PPO₂ of about 0.16 bar. Flushing the loop with it there could knock you out. A breathable dilout restores the diluent flush as a usable tool during the long shallow stops.
3. No extra bottle. The deep bailout stage is already on your hip. Plugging it in as diluent costs nothing and spares the small onboard bottle.

Each switch row takes a depth and the gas, picked from your OC cylinders (the onboard diluent is also an option, so you can switch back to it shallower). The same smallest-depth-wins rule as the setpoint schedule decides which switch is in force at each stop.

On a dive profile, each level can also choose its loop diluent in the level editor, for the rare case of riding a dilout during a section of the bottom phase. Levels set to Auto always breathe the onboard diluent; the planner never switches diluents for you.

Setpoints

A setpoint is the loop oxygen partial pressure, in bar, that the unit holds during a phase of the dive. Setpoints are always shown in bar regardless of your depth or pressure unit. The Setpoints sheet covers three setpoints plus the descent switch depth:

Setpoint	Default	When it applies
Descent	0.7 bar	The initial descent only, from the surface down to the switch depth (or the first level, whichever you reach first). A low value lets you flush the loop early without going hyperoxic in the shallows.
Switch depth	18 m	Not a setpoint but a depth: where the loop hands over from the descent setpoint to the bottom setpoint.
Bottom	1.0 bar	Your working PPO₂ at depth. A higher bottom setpoint shortens deco.
Deco	1.4 bar (base)	The PPO₂ during the ascent and deco stops. A higher value off-gasses faster.

You type each setpoint in bar, in 0.1 steps. A typical bottom setpoint sits around 1.0 to 1.3, and the in-app help caps the working phase at 1.4; you push the deco setpoint higher (toward 1.6) where the depth allows, because a higher PPO₂ off-gasses faster.

The descent setpoint applies only to that first descent, not to later descents within a multi-level dive.

Deco setpoint schedule

One deco setpoint is enough: set the base value “from start of deco” and the whole ascent runs on it. To shave deco you can step the setpoint by depth. Add changes such as 1.5 at 12 m and 1.6 at 6 m, and a lower value like 1.2 at 3 m where 1.6 can no longer be held. The deepest matching change applies at each stop. The schedule is setpoints only; planned diluent switches live in their own list (see Diluent switches).

The engine caps any setpoint at what the loop can physically reach, because a loop PPO₂ can never exceed the ambient pressure. A value set too high for a shallow stop (1.6 needs roughly 6 m or deeper) is simply run at the achievable PPO₂; you stay on the loop rather than being forced off it. The planner shows an info warning when a setpoint you configured can not be held at a stop deeper than that, so you can lower it if you meant it literally.

Oxygen break setpoint

When the plan inserts oxygen breaks during long high-PPO₂ stops, you can have those breaks apply on the loop too. This is off by default. Turn on Apply on CCR loop in the plan’s Oxygen Breaks settings, and the loop setpoint drops to the O₂ Break Setpoint (default 0.7 bar) during each break. With it off, oxygen breaks still apply to your Open Circuit bailout schedule but the loop schedule stays manual.

Open Circuit bailout

The planner does not have a separate bailout manager. The Open Circuit cylinders you add to the gas list (titled OC / Bailout Gases once CCR is on) serve as your bailout supply. The planner computes a full OC ascent on those gases so you can confirm you carry enough to get out, and it checks that a bailout gas covers your deepest point and your last depth.

Above the deco table, a row of view chips lets you switch what the table and graph show for the current scenario:

• CCR is the on-loop ascent. This is the default view.
• Full Bailout is the OC ascent if you come off the loop and bail from the bottom.
• Bailout at X lets you add a switch depth: the plan stays on the loop down to X, then completes the rest of the ascent on Open Circuit. Add as many switch depths as you want to study.

The bailout views read yellow on the graph and table to distinguish them from the loop plan.

How CCR changes the schedule and gas view

A CCR plan differs from an OC plan in a few visible ways:

• The schedule is built from setpoints, not from a fixed gas. The loop PPO₂ at each phase comes from the setpoints you set, and the deco table labels each stop with the setpoint in force. A stop riding a dilout also names the mix (“SP 1.4 · 18/30”); stops on the onboard diluent show the bare setpoint, so the mix tag is your cue that a switch is in force.
• Setpoint changes appear as their own rows. Each setpoint or diluent change on the ascent shows as a marked switch in the table, including the bottom-to-deco setpoint bump at the start of deco.
• Gas required splits into loop gas and bailout gas. The Gas Required view shows your O₂ cylinder and the onboard diluent cylinder, then your OC bailout cylinders. Oxygen use is the metabolic top-up (depth independent). Diluent is drawn by compressing the loop on descent, plus a flush allowance, plus two loop flushes for every diluent switch, costed at the switch depth: a 6 L loop switched at 30 m draws about 48 L from the incoming cylinder, because each flush refills the loop’s volume at 4 bar of ambient pressure. A cylinder used as a dilout shows that draw on its own row, marked “dilout”. On the loop view its remaining pressure counts only that dilout draw. A bailout view pairs the open-circuit bailout draw with the loop gas you actually breathe before bailing, and skips diluent switches the bailout never reaches, so the two roles are never double-counted against the same bottle. And if breathing it as diluent plus the bailout plan together need more gas than the cylinder holds, the planner warns you with the shortfall.

Rig defaults

When you first enable CCR on a plan, the planner copies a full CCR Rig once from your defaults. After that the copy is the plan’s own; later changes to your defaults are not pushed into it. The seeded defaults are:

Setting	Default
Diluent	21/0 (air)
Descent setpoint	0.7 bar
Bottom setpoint	1.0 bar
Deco setpoint	1.4 bar base, stepping to 1.5 at 40 m and 1.6 at 23 m
O₂ break setpoint	0.7 bar
Switch depth	18 m
O₂ cylinder	3 L at 200 bar
Diluent cylinder	3 L at 200 bar
Loop volume	6 L

You can change the rig template under Edit Defaults so every new CCR plan starts from your own configuration. Edit the values per plan in the CCR section as above.

Sources on diluent switching

Diluent switching is a niche, advanced practice. These are the sources behind the feature, each verified against the original document:

• MultiDeco user guide (HHS Software). The de-facto standard technical planning software supports diluent changes inside a CCR plan, with the worked example “change to air diluent, and 1.4 at 20m”. Dive Kit’s diluent switches model the same capability.
• Shearwater Perdix Operations Manual, “Select Gas” and “CC Gases” sections. Shearwater computers carry five closed-circuit gas slots (“the closed circuit diluent gases… displays all five gases simultaneously”) and let the diver switch the active diluent mid-dive. Carrying and switching among several diluents is a supported, real-world workflow.
• Stéphane Havard, “Understanding and safe use of PPO2 set-points for CCR” (2002), hosted at ccr-training.com. A practitioner account: “I usually use now a diluent change when it will shorten the deco of at least 15-20 minutes in cold water. I switch then from a 8/62 bottom diluent to an air or a nitrox 32 deco diluent at 40 meters.” The same paper explains diluent-flush mechanics (the loop resets to the diluent’s PPO₂ at depth) and notes honestly that the practice divides divers from the “one-gas-all-the-way” school.
• Silent Diving (AP Diving’s Americas distributor), “Which CCR Diluent Fits Your Dive Profile?”. Confirms the surface-breathability constraint on diluents and that diluent switching “is a more advanced configuration and not necessary for most dive profiles”, which is exactly how Dive Kit treats it: empty by default, opt-in per plan.

The claimed decompression benefit is the debated part; the shallow-flush safety argument and the gas logistics are not. Treat a diluent switch as a technique you bring from training, not one a planner talks you into.

Related

• Deco Planner covers the rest of the planner: gases, levels, gradient factors, contingencies, and reading the results.
• How the engine works explains the Bühlmann ZH-L16C tissue model behind the schedule.
• Assumptions and limits lists the engine’s references, including the sources above.