---
title: "Gases and mixes"
weight: 30
description: "Declaring your open circuit mixes, your cylinders (volume and pressure), your bailout gases and your CCR diluents in MV-Plan."
source_hash: 203b3e12a88f
---

# Gases and mixes

The Gases page is where you declare the mixes you carry: air, nitrox, trimix, decompression gases, bailout gases and, in rebreather mode, the diluents.

![Gas management page with the list of mixes](screenshots/gaz-liste.webp)

## List of mixes

Mixes are sorted by decreasing oxygen content. Each one shows:

- a **switch** to enable or disable it (only enabled gases are offered in the segments);
- the **name** of the gas;
- the **composition**: percentage of O2, of helium (He) and of nitrogen (N2, worked out automatically);
- the **MOD** (maximum operating depth) and the **END** (equivalent narcotic depth) at the MOD;
- the **ppO2 max** that is set;
- the **tank configuration**: volume (L), pressure (bar) and total capacity (L);
- the **Edit** and **Delete** buttons.

## Adding a mix

Click **Add**. A dialog opens:

- **Auto label**: when on, the name is built from the composition (for instance "21/35" for a trimix). Turn it off to type a name of your own.
- **O2 %**: oxygen percentage (5 to 100).
- **He %**: helium percentage (0 to 95).
- **N2 %**: worked out automatically (100 - O2 - He).
- **ppO2 max**: maximum oxygen partial pressure (0.8 to 1.6 bar). The matching **MOD** and **END** are computed and shown as you type.
- **Use as bailout gas**: marks the gas as available for an emergency way out.
- **Tank configuration**: cylinder volume (1 to 50 L) and fill pressure (100 to 300 bar). The total **capacity** (volume x pressure) is shown automatically.

Confirm with **Save**.

![Add mix dialog with the MOD and END being computed](screenshots/gaz-ajout-melange.webp)

## Editing or deleting a mix

- **Edit**: reopens the dialog with the existing values.
- **Delete**: removes the mix after confirmation.

## Bailout gases

A gas marked "Use as bailout gas" feeds the open circuit bailout simulation in rebreather mode (see [CCR mode](/mvplan/mode-ccr)). On plain open circuit, your decompression gases play that part.

## Diluents (CCR mode)

Once rebreather mode is enabled in the [Settings](/mvplan/reglages), a second list appears: the **diluents**.

- Each diluent shows its composition, its MOD (based on a 1.6 bar ppO2 max) and its END at the current setpoint.
- The diluent in use is highlighted.
- Adding and editing work as for a mix, but without tank configuration and without the bailout flag. O2 content is limited to 5-21 % and helium to 0-90 %.

At least one diluent must always remain: the last one cannot be deleted.

**Oxygen** is declared nowhere: a rebreather is dived on two cylinders, a diluent and pure oxygen, which is exactly why a diluent is capped at 21 % O2. Finishing the dive on oxygen is set directly in the CCR Mode block of the [Settings](/mvplan/reglages).

For the detail of how the rebreather works, see the [CCR mode](/mvplan/mode-ccr) page.