Gas Management
END & Trimix Calculator
Calculate partial pressures and Equivalent Narcotic Depth under a named convention. Results explain one model; they do not recommend a trimix or safe depth.
Depth and breathing gas
Nitrogen is calculated as the remainder after oxygen and helium. All pressure outputs are absolute ATA.
Quick examples
Load a complete depth-and-gas scenario, then adjust any value below.
m
Allowed range: 0 to 200 m.
%
Allowed range: 0 to 100 %.
%
Allowed range: 0 to 100 %.
Tx21/35
O₂ + N₂ narcotic; helium non-narcotic
Equivalent Narcotic Depth
35.5 m
Named planning convention
PPO₂ at depth
1.47 ATA
1.4 ATA selected threshold
MOD at 1.4 ATA
56.7 m
- Absolute pressure
- 7.00 ATA
- Calculated nitrogen
- 44.0%
- PPN₂
- 3.08 ATA
- PPHe
- 2.45 ATA
- Narcotic partial pressure (PPO₂ + PPN₂)
- 4.55 ATA
Selected PPO₂ threshold exceeded
The selected PPO2 threshold is exceeded at this depth.
Theoretical helium for a target END
This reverses only the named END equation while holding oxygen constant. It does not recommend a mix.
m
Allowed range: 0 to 200 m.
Theoretical helium
42.86%
Before operational rounding
Remaining nitrogen
36.14%
Educational inversion only
END does not evaluate gas density, work of breathing, decompression, thermal effects, helium-related tradeoffs, available gases, training, or whether a rounded mix is appropriate.
The convention used
This calculator counts oxygen and nitrogen as equally narcotic and helium as non-narcotic. Another convention can give a different END.
Where
- helium fraction, not percentage (0.35 for 35%)
- actual depth (m)
- 10 m of seawater per atmosphere
The model assumes 1 ATA at the surface.
What END cannot tell you
A lower calculated END is not proof of clear thinking and is not a safe-depth result. Susceptibility, carbon dioxide, workload, cold, and individual response still matter.