The descent is gradual. The loop warms, the vision clears, and the wall falls away beneath you in bands of blue and shadow. No bubbles rise. No exhaust stream betrays your presence. On open circuit, you would already be watching your pressure gauge and calculating gas reserves, knowing the dive is half over before the wall has truly begun. On a closed-circuit rebreather, the calculation shifts. Gas management, setpoint selection, diluent choice, bailout planning, and decompression strategy form a unified discipline that differs fundamentally from open-circuit planning. Silent Diving has supported rebreather divers across the Americas for more than twenty years. We have watched the planning tools mature and the training pathways solidify. This post walks through how CCR dive planning differs from open circuit, how to manage setpoints and diluents, how to size bailout gas, and why decompression planning on a rebreather demands a different approach–and different software.
Whether you are preparing for your first technical CCR course or refining your extended-range planning, understanding these concepts before you descend will sharpen your discipline and improve your safety. We cover the essentials: PO2 setpoints and when to switch them, diluent selection by depth, bailout calculations and redundancy, decompression advantages of the closed circuit, and the software tools that support AP Diving rebreathers across recreational and technical profiles.
How CCR Dive Planning Differs from Open Circuit
Open-circuit planning centres on gas consumption: how much gas you carry, how fast you breathe it, and how long it lasts. Your consumption rate–typically expressed in litres per minute or cubic feet per minute–drives every calculation. On a rebreather, that arithmetic changes. The loop recycles your exhaled gas. Oxygen is added on demand. Diluent is used mainly for loop volume maintenance and bailout, not as your primary breathing medium throughout the dive. As a result, consumption rates for oxygen and diluent are far lower than open-circuit consumption. What does not change is the need for rigour: bailout gas must still be calculated and carried, decompression obligations must still be planned, and equipment failures must still be anticipated.
CCR planning introduces variables that open-circuit divers seldom consider. Setpoint–the partial pressure of oxygen you target in the loop–affects narcosis, oxygen toxicity risk, and decompression efficiency. Diluent selection determines what gas is available if the loop is flooded or you must bail out at depth. Scrubber life constrains bottom time independent of gas volume. The dual controllers that maintain setpoint automatically–AP Diving’s C1 Master and C2 Slave–free you from manual oxygen addition, but they do not free you from understanding the underlying physics and planning accordingly. Software that understands rebreather profiles, setpoint switching, and diluent options becomes essential for technical diving.
PO2 Setpoints: Low, High, and When to Switch
The partial pressure of oxygen in your breathing gas determines how efficiently you clear inert gas and how much risk you accept from oxygen toxicity. On a rebreather, you set a target PO2–the setpoint–and the controllers maintain it automatically. Most CCR divers use two setpoints: a low setpoint for descent and decompression, and a high setpoint for the working phase of the dive. Understanding when and why to switch between them is core to rebreather discipline.
Low Setpoint: 0.7 and Below
Low setpoint (0.7 ATA): Used during descent and during decompression stops. At shallow depth, a low setpoint reduces the risk of hyperoxia and central nervous system oxygen toxicity. During decompression, a lower PO2 keeps you within conservative oxygen exposure limits while still accelerating offgassing compared to air. Many divers run 0.7 during the shallow phases of the dive and during stops. The trade-off is slightly slower inert gas elimination at depth, which is why most divers switch to a higher setpoint once they reach the working depth and before they ascend.
High Setpoint: 1.2 to 1.3
High setpoint (1.2–1.3 ATA): Used during the working phase of the dive, when you are at or near maximum depth. A higher PO2 accelerates offgassing and reduces decompression obligations. It also increases the partial pressure of oxygen in your tissues, which improves inert gas elimination. The limit is oxygen toxicity: extended exposure above approximately 1.6 ATA increases the risk of convulsions. Technical divers typically use 1.2 or 1.3 as their high setpoint, staying well below that threshold. AP Diving dual controllers C1 and C2 maintain the setpoint automatically; you select the value, and the electronics do the rest.
When to Switch
Switching typically occurs at a predetermined depth. Divers often ascend to a shallow threshold–for example, 20 metres or 60 feet–and switch from high to low setpoint before continuing the ascent and decompression. The exact depth depends on your training, agency guidelines, and conservatism. Switching too late risks hyperoxia in the shallower water column. Switching too early extends decompression time. Your instructor and your software will help you establish a protocol that fits your profile and risk tolerance.
Diluent Selection: Air, Trimix, and Heliox by Depth
Diluent is the gas used to maintain loop volume and to flush the loop when necessary. It is also the gas you breathe if you bail out at depth. Diluent must be breathable at your maximum operating depth–hypoxic at depth means diluent cannot be used for bailout. The choice of diluent depends on your planned depth and your decompression strategy.
Air as Diluent
Air diluent: Suitable for recreational rebreather profiles–typically to 40 metres or 130 feet. Beyond that, the nitrogen load and narcotic effect increase, and oxygen partial pressure at depth on air can approach toxic levels when combined with a high setpoint. Air is simple, widely available, and adequate for many warm-water reef and wreck dives. If your planned depth stays within recreational limits and your training supports it, air diluent is often the default.
Trimix and Heliox for Extended Range
Trimix diluent: A blend of oxygen, nitrogen, and helium used for deeper technical profiles. Helium reduces narcosis and density, making breathing easier at depth. Trimix diluent allows you to run a high PO2 setpoint while keeping the inert gas component breathable and manageable. Mix selection–the precise ratio of He, N2, and O2–depends on your maximum depth and your bailout strategy. Software such as AP Diving’s Projection Dive Planner supports trimix planning and helps you model different mixes for bottom gas, travel gas, and decompression.
Heliox diluent: Oxygen and helium only, no nitrogen. Used in very deep or long-duration technical diving where nitrogen loading must be minimised. Heliox requires careful management of oxygen partial pressure and is typically the domain of extended-range and exploration divers. Upgrades to your rebreather software–often available through Silent Diving’s service team–enable trimix and extended-range planning. The Vision display on AP Diving units integrates with Bühlmann deco algorithms to show real-time decompression status; ensuring your software is current ensures your planning matches the unit’s capabilities.
Bailout Gas: Minimum Volume, Redundancy, and Calculation
Bailout is your open-circuit escape route when the rebreather fails. It is not optional. It is gas you must carry, calculate, and be prepared to use. Bailout planning answers two questions: how much gas do you need, and what mix should it be? Both depend on your planned profile, your decompression obligations, and the gas you and your buddy will breathe.
Minimum Volume and Consumption Assumptions
Bailout consumption rate: Plan for elevated breathing–stress and cold increase demand. Many divers use 40 litres per minute or higher when calculating bailout volume. The calculation is straightforward: depth, time from deepest point to surface, decompression stops, consumption rate, and reserve. Include gas for your buddy if you are the primary bailout carrier. Factor in reserve for contingencies: currents, delays, or a second bailout. Technical divers typically carry sufficient gas for a full ascent and decompression on open circuit. Our post Understanding Rebreather Safety: Oxygen Sensors, Scrubbers, and Bailout Planning covers bailout calculation in detail alongside oxygen sensor and scrubber considerations.
Redundancy and Pre-Dive Verification
Redundancy: Some profiles warrant multiple bailout stages–one for bottom phase, one for decompression–or redundant cylinders for the same phase. The principle is simple: if one stage fails or is insufficient, you must have another. Pre-dive verification of bailout cylinders, mix, pressure, and depth compatibility takes thirty seconds and can save your life. Confirm that each cylinder is full, correctly labelled, and breathable at the depth where you might need it. Carrying the wrong mix–or gas that becomes hypoxic or hyperoxic at your planned depth–defeats the purpose of bailout.
Decompression Advantages on Closed Circuit
Closed-circuit rebreathers offer significant decompression advantages over open circuit. The primary benefit is control over oxygen partial pressure: you can maintain an optimal PO2 for offgassing throughout the ascent and stops. On open circuit, decompression gas is fixed–you breathe what you have, and PO2 varies with depth. On a CCR, you hold a setpoint that maximises inert gas elimination while staying within oxygen exposure limits. The result is shorter decompression schedules for equivalent profiles, or the ability to extend bottom time for the same decompression obligation.
AP Diving units use Bühlmann decompression algorithms implemented in the Vision display. The system calculates real-time decompression status based on your depth, setpoint, and time. Software upgrades–available through our service department–unlock trimix and extended-range planning, ensuring your surface planning matches what the unit displays underwater. The dual controllers maintain setpoint without manual intervention, so you can focus on monitoring the display and executing the plan.
Software Tools for CCR Dive Planning
Rebreather dive planning software must understand closed-circuit profiles: setpoint switching, diluent options, oxygen and diluent consumption, and decompression algorithms compatible with your unit. Generic open-circuit planners do not model these variables correctly. AP Diving’s Projection Dive Planner and the planning modules integrated with the Vision system are designed for the platform.
Projection Dive Planner and Vision Integration
Projection Dive Planner: AP Diving’s planning software supports setpoint selection, diluent configuration, bailout calculations, and decompression modelling. It allows you to build profiles before the dive, test different setpoint strategies, and verify that your bailout gas is sufficient. The software integrates with the Bühlmann algorithms used in the Vision display, so surface plans align with what you see underwater.
Software key upgrades: Trimix and extended-range planning often require software key upgrades. These unlock additional mix options, deeper profiles, and more advanced decompression models. Silent Diving, as the authorised service center for the Americas, can process these upgrades and ensure your software matches your certification and diving goals. If you are progressing beyond recreational CCR into technical or extended-range profiles, verifying your software version and upgrade status is part of sound planning.
Planning as Discipline
Rebreather dive planning is not a one-time exercise. It is a discipline you apply before every dive: setpoint selection, diluent verification, bailout calculation, scrubber life check, and software confirmation. The AP Diving Inspiration and Evolution–with dual C1 and C2 controllers, Vision display, and Bühlmann deco integration–give you the tools to execute that discipline. What they cannot do is replace the planning that happens before you step into the water.
If you are preparing for your first CCR certification, our post What to Expect from Your First CCR Certification Course walks through prerequisites, course structure, and what you will learn about gas management and planning. For a deeper look at the safety systems that underlie every dive plan–oxygen sensors, scrubbers, and bailout–our post on Understanding Rebreather Safety covers the foundations. Silent Diving maintains a network of twenty-two approved instructors across the Americas who can help you build and refine your planning discipline. We invite you to explore our rebreathers page for specifications on the Inspiration and Evolution, reach out through our contact form with questions about planning software and upgrades, or connect with our service team for maintenance and software key upgrades. The wall is waiting. Plan well, and descend with confidence.
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