MOD / EAD / END¶
The MOD / EAD / END calculator analyzes an existing gas mix: how deep it's safe, how narcotic it is, and how dense it gets.
Open via App menu → Tools → MOD / EAD.
Inputs¶
| Field | What it controls |
|---|---|
| O₂ % | Oxygen percent of the mix (5–100) |
| He % | Helium percent (0–95). N₂ is the balance. |
| Depth (m) | Target depth. Pre-filled with the deepest segment of your active plan. |
| PPO₂ limit (ata) | Max allowed PPO₂ for the calculation. Default 1.40. |
The Mix display shows the combined O₂/He notation for clarity.
Outputs¶
| Result | Meaning | Color logic |
|---|---|---|
| MOD | Max operating depth at the configured PPO₂ limit | Red if < target depth, neutral otherwise |
| PPO₂ at depth | The actual PPO₂ this mix delivers at the target depth | Yellow > limit, red > 1.6 |
| EAD | Equivalent Air Depth — N₂ narcotic only, He treated as inert (most agencies' planning standard) | Yellow > 40 m |
| END | Equivalent Narcotic Depth — N₂ + O₂ both narcotic (GUE method) | Yellow > 40 m |
| EADD | Equivalent Air Density Depth — at what air depth the same density would occur | Informational |
| Gas density | At the target depth (15 °C reference) | Yellow ≥ 5.2 g/ℓ, red ≥ 6.2 g/ℓ |
Definitions¶
MOD (Max Operating Depth)¶
At MOD, the PPO₂ exactly equals the configured limit. Going deeper exceeds it.
For 21 % O₂ at PPO₂ 1.4: MOD = (1.4 / 0.21 − 1) × 10 ≈ 57 m.
EAD (Equivalent Air Depth — N₂ only)¶
The depth at which air alone would deliver the same N₂ partial pressure as your mix at the current depth. The standard planning measure for narcosis on agencies that treat O₂ as non-narcotic (most: PADI, TDI, SDI, IANTD, RAID).
END (Equivalent Narcotic Depth — N₂ + O₂)¶
Treats both N₂ and O₂ as narcotic, helium as inert. Used by GUE and a few other agencies. Always shallower than EAD for the same mix (because O₂ adds to the narcotic load in this model).
EADD (Equivalent Air Density Depth)¶
The air depth that produces the same gas density. Useful for density-conscious planning: if your mix's EADD is 50 m, it's as dense as air at 50 m, regardless of its narcotic equivalent.
Gas density¶
The mass per litre of the mix at the target depth, computed at 15 °C reference.
Worked example¶
Mix: 16/58 trimix at 75 m, PPO₂ limit 1.40
| Result | Value |
|---|---|
| MOD | 77 m (1.4 / 0.16 − 1) × 10 |
| PPO₂ at depth | 1.36 ata (0.16 × 8.5) |
| EAD | 13 m ((1−0.16−0.58) × 8.5 − 10) |
| END | 26 m ((1−0.58) × 8.5 − 10) |
| EADD | ~50 m |
| Gas density | 5.06 g/ℓ |
Reading this:
- MOD 77 m at 1.4 → fine, you're at 75 m so well within
- EAD 13 m → minimal narcosis (vs air at 13 m), excellent
- END 26 m → if you follow GUE method, still acceptable
- Density 5.06 g/ℓ → green (just under 5.2 guideline)
Practical use¶
- Verify a bottom gas before plugging it into a plan. If MOD < target depth, change the mix.
- Compare narcosis between mixes. Two trimix options for the same depth can have noticeably different EADs.
- Density sanity check. Especially relevant when the dive depth approaches 50+ m and you're using nitrox-heavy trimix.
- PPO₂ alarm. If the PPO₂ at depth turns red (>1.6), the mix is acutely dangerous at this depth.
Comparing EAD vs END¶
For a 16/58 trimix at 75 m:
- EAD = 13 m (treating O₂ as non-narcotic)
- END = 26 m (treating O₂ as narcotic)
The 13 m difference (the contribution of O₂ to narcotic load in the END model) is significant on paper but smaller in practice. Most agencies don't differentiate. Pick the one matching your training and stick to it.