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 levels and the shape of the screen, and Gases in the Deco Planner for the open-circuit cylinders you carry as bailout.

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 setpoints, diluents and switches back rather than the defaults. The one thing that does not come back is a setpoint you pinned to an individual dive level, which is reset to the rig’s bottom setpoint.

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
Breathable open circuit	Tick it when your BOV is plumbed to the diluent cylinder, or it carries an open-circuit regulator	Bailout plans may then breathe the diluent, and those litres come off the same bottle as your loop. See The onboard diluent as a bailout gas
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, computed at the plan’s water density, so it is the same figure the CCR card shows. 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 opens in one of two views. When your rig runs one setpoint from the surface through the bottom phase, with a single deco setpoint and no diluent switches, you get the simple view: a Setpoint field and a Deco field, nothing else. Tap Advanced setpoint options to open the full model below. A rig that already uses a descent setpoint, a stepped deco schedule, or a diluent switch opens straight into the full view, where a Use simple setpoints action flattens everything back to one setpoint per phase (diluent switches are never deleted by it; remove those yourself first).

The full view 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. Each change reads as “at this depth and shallower”, so add them 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. At each stop the planner uses the shallowest change that still covers it, so on that schedule the base setpoint runs down deep, 1.5 from 12 m up to 7 m, 1.6 from 6 m to 4 m, and 1.2 at 3 m. 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 your last planned depth. On a single-level dive that is the bottom; on a multi-level profile it is the depth of your last level, which may be shallower than your deepest.
• 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.

A plan with no bailout gas at all greys both bailout chips out, since there is no open-circuit ascent to draw. If one of them was selected when the last bailout gas went, whether you removed the last stage bottle, unticked Breathable open circuit on a diluent that was carrying the job alone, or turned CCR off, the planner drops back to the CCR view. Shared plans, duplicates and contingency variants are checked the same way as they open, so a plan never lands on a bailout view it cannot fly.

The onboard diluent as a bailout gas

Many rebreathers let you breathe the diluent open circuit, through a bailout valve in the mouthpiece or a second stage on the same cylinder. If yours does, tick Breathable open circuit under the diluent in the CCR Gases sheet. The CCR card then shows an OC bailout tag next to your diluent mix, whether the card is open or collapsed. The tag says the cylinder is in the bailout pool, so it is not confused with the OC badge a dive level carries when that leg is dived off the loop.

You can dive it with no stage bottles at all. The Gases card then says so, with a line reading that your diluent is your bailout gas, instead of the “add a bailout gas” warning a rig with nothing breathable would get.

With it on, the planner treats the diluent as one more bailout gas. It joins the pool last, which sets the order you would use yourself:

• Where an offboard cylinder is at least as good at that depth, the plan breathes the offboard bottle first. A 3 L diluent is a few minutes of gas at depth, so you would not spend it while a stage bottle will do.
• The diluent takes over when the offboard bottle runs out, if the plan’s When a cylinder runs out setting is Switch gas, and wherever the diluent is simply the best gas you carry for that depth.

Whatever the loop already drew from the cylinder is gone before any of that. The Gas Required view keeps one row for the bottle and one number on it, counting the loop draw and the open-circuit draw together, so the pressure it shows is what you would expect to see on that cylinder at the surface. A line under that row, Loop before bailing: 320 L, says how much of it the loop took before you bailed, which is the figure that tells you whether a 3 L diluent is worth counting as bailout at all. On a Bailout at X view the loop draw counted includes the ride down from your profile to X, so a diluent switch in that band is charged before the bailout starts; on Full Bailout you leave the loop at your last planned depth, so there is no loop ascent to charge. Open-circuit rows that breathe it are labelled 18/45 · diluent in the deco table’s Mix column, so you can see which bottle each stop is emptying.

Leave the box unticked if your diluent has no bailout valve or regulator on it. The planner then keeps it out of the bailout pool entirely, which is what it did before 2.9.0.

With the box ticked, the bailout views and the bailout checks work even if you carry no stage bottles at all, because the diluent is the bailout. Untick it on a plan with no other gas and the planner goes back to saying you have no bailout, which is then true.

A dilout is the reverse arrangement: an offboard cylinder feeding the loop as diluent, set up under Diluent switches. The two can be true of the same dive, and they are configured in different places.

The bailout check runs on every view

You do not have to open the Full Bailout view to learn that your bailout is short. The planner checks the worst-case bailout from your last planned depth whenever it computes a plan, and raises a critical warning on whatever view you are looking at, because the loop view is exactly where the problem is easy to miss: it reports your bailout cylinders at or near their fill pressure, since the loop barely touches them, and a bottle that reads full on the loop view can still be far too small for the ascent it would have to cover. When the check fires, the Full Bailout chip turns red so you know which view explains it.

Four things can be wrong, and the warning says which:

Warning	What it means
Not enough bailout gas in gas	A bailout cylinder cannot cover the ascent it is carried for. The warning names the shortfall
Not enough bailout gas in Diluent mix	Your diluent is ticked Breathable open circuit, and the loop draw plus the open-circuit draw together need more than it holds
Not enough gas in gas for dilout plus bailout	You also breathe that cylinder as a dilout, and the two roles together need more than it holds
Bailout leaves gas below its reserve	It covers the ascent, but finishes under the reserve you set for that cylinder under Advanced in the gas sheet

The last one fires only on a reserve you typed for that specific cylinder. It never fires on the onboard diluent, which has no per-cylinder reserve field of its own. Your global reserve rule (thirds, sixths, and so on) is a turn-pressure rule for bottom gas and says nothing useful about an emergency bailout, so it is deliberately left out of this check.

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. Once a plan uses a dilout, every loop row also names its diluent so you can read what is in the loop at a glance: the onboard diluent reads bare (“SP 1.4 · 18/45”) and a dilout is wrapped in brackets (“SP 1.4 · [18/30]”), the cue that this row breathes a bailout cylinder as diluent. Plans that never leave the onboard diluent keep the bare setpoint (“SP 1.4”) so the column stays uncluttered. An optional Equivalent Mix toggle below the table adds the open-circuit mix the loop behaves like at each depth, marked with a ≈ (”≈ 30/0”).
• 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. A diluent ticked Breathable open circuit works the same way in the other direction: on a bailout view its Diluent row adds the litres the bailout breathes from it to the litres the loop already took, and reports one remaining pressure for the one bottle. There is no second row for it. Bailout consumption is charged in two phases: your Working SRMV from the bail point up to the first deco stop, then your Deco SRMV from that stop to the surface. Swimming off a failed loop at depth is work, so it is priced as work. The bailout schedule uses your plan’s gradient factors, and there are still no separate bailout settings. To size bailout for a stressed exit, add a Stress SRMV burst: a higher rate for a Duration you set, which can cover the whole ascent. All four plan modifiers live in one sheet, opened from the Modifiers line under the view chips. The two rate rows stay visible on the loop view, labelled as open-circuit gas rates, because they are what the bailout views and the bailout gas check run on: they do nothing to the loop itself. Modifiers belong to a contingency tab or to the whole plan, not to a view: open the sheet on a bailout view and you are editing the tab that view sits on, which the sheet says under Applies to. The view still decides where they bite, so a stress burst on a Bailout-at-X view starts when you leave the loop and a delay is held at the bailout depth on the bailout gas. 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, on every view. A dive level you set to breathe open circuit instead of the loop is charged to the cylinder you pick for it, descent and bottom time both, at your Working SRMV. Before 2.9.0 that gas was counted nowhere, so the card showed more left than you would have had.

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 232 bar
Diluent cylinder	3 L at 232 bar
Loop volume	6 L

Diluent switches are not part of the template. A switch points at one of the plan’s own Open Circuit bailout cylinders, and your defaults have no cylinder list to point at, so switches are set per plan and are never seeded. The Diluent switches section on the defaults screen says so in place of an Add control.

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: levels, saved plans, and the shape of the screen.
• Gases in the Deco Planner is the reference for the open-circuit cylinders you carry as bailout.
• Reading a deco plan explains the stop table, the gas cards, and every warning named on this page.
• Contingencies and plan modifiers covers the scenario tabs the view chips combine with.
• 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.