ENDEquivalent Narcotic Depth
Equivalent Narcotic Depth of a breathing gas is an estimate of a depth with the same narcotic effect if breathing air.
Helium is not narcotic, so adding it keeps your head clear at depth. END tells you how deep a trimix feels compared with breathing air.
How it works
END = (depth + 10) × (1 − FHe) − 10
- FHe helium fraction of the gas
- O₂ is not narcotic switch it on to count nitrogen only: END = (depth + 10) × FN₂ ÷ 0.79 − 10
Example
- Gas
- 10 % helium
- Depth
- 40 m
- END
- 50 × 0.90 − 10 = 35 m
How it works
END = (depth + 32.8) × (1 − FHe) − 32.8
- FHe helium fraction of the gas
- O₂ is not narcotic switch it on to count nitrogen only: END = (depth + 32.8) × FN₂ ÷ 0.79 − 32.8
Example
- Gas
- 10 % helium
- Depth
- 120 ft
- END
- 152.8 × 0.90 − 32.8 ≈ 105 ft
Take it to the dive site
The same calculator works offline in the Deep Tools app, together with the dive planner, dive log and blender.
