What is nitrogen narcosis?

Nitrogen narcosis (also called 'rapture of the deep') is a reversible alteration in consciousness produced by the narcotic effect of inert gases at elevated partial pressures. The mechanism follows the Meyer-Overton correlation: narcotic potency correlates with lipid solubility. Symptoms typically begin around 30 meters (100 feet) on air and worsen with depth.

Does nitrox reduce narcosis?

No. This is a common misconception. Both nitrogen and oxygen have essentially equal narcotic potency at depth. When you replace nitrogen with oxygen in nitrox, you're simply swapping one narcotic gas for another. Your total narcotic partial pressure (ppN₂ + ppO₂) remains the same at any given depth. Nitrox provides decompression benefits but NOT narcosis reduction.

What is Equivalent Narcotic Depth (END)?

END is the depth at which breathing air would produce the same total narcotic partial pressure as your actual breathing gas at the actual depth. Formula: END = (1 - He%) × (Depth + 10) - 10. For example, diving at 60m on Tx21/35 (35% He) gives an END of ~35.5m - significantly less than the actual depth.

How does helium reduce narcosis?

Helium has negligible narcotic potency (approximately 4.26× less than nitrogen). It's effectively non-narcotic for practical dive planning. By replacing nitrogen and oxygen with helium in your breathing mix, you reduce the total narcotic partial pressure at depth, which lowers your END. This is the fundamental reason trimix exists - to enable deeper diving with manageable narcosis levels.

What is the recommended maximum END?

Most training agencies recommend keeping END at or below 30m for technical dives. PADI Tec Deep: 30m, TDI: 30-35m, GUE: 30m, IANTD: 30m, NAUI Tech: 35m. These are conservative starting points - individual susceptibility varies significantly. For experienced technical divers in non-training contexts, 30-40m is the universal planning standard.

What is the difference between END and EAD?

When using the same formula (END = (1 - He%) × (D + 10) - 10), they're mathematically identical! The difference is interpretation: EAD (Equivalent Air Depth) is used for decompression calculations (how nitrogen absorption compares to air), while END is used for narcosis risk assessment. Both metrics are useful for different purposes in dive planning.

Does trimix reduce narcosis?

Yes, trimix effectively reduces narcosis by replacing narcotic gases (nitrogen and oxygen) with non-narcotic helium. The higher the helium fraction, the lower your Equivalent Narcotic Depth. For example, diving at 60m on Tx21/35 (35% He, 44% N₂, 21% O₂) produces an END of only ~35.5m compared to 60m on air. This makes deep diving safer and more comfortable.

What is oxygen narcosis?

Oxygen has narcotic potency essentially equal to nitrogen at depth (approximately 1:1 on a molar basis). At 30m, the partial pressure of oxygen in air is 1.26 bar - contributing significantly to total narcotic load. This is why nitrox (which simply replaces nitrogen with oxygen) does NOT reduce narcosis. You're swapping one narcotic gas for another. Only helium, which has negligible narcotic potency, can reduce narcosis.

How to calculate trimix composition?

To calculate trimix composition: (1) Determine your target END (typically 30m), (2) Calculate required helium: He% = 1 - (END_target + 10) / (depth + 10), (3) Calculate optimal oxygen for your MOD: FO₂ = ppO₂_max / P_abs. Our calculator automates this process - just enter your depth and target END to get the recommended trimix blend with helium, oxygen, and nitrogen percentages.

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Nitrogen Narcosis & Equivalent Narcotic Depth (END) Calculator

Calculate the Equivalent Narcotic Depth (END), narcotic load, and narcosis risk for any breathing gas at any depth. Plan trimix composition to reduce narcosis at depth.

Narcosis Risk

Low

Equivalent Narcotic Depth (END)

30.0 mt

At 30 meters with Air, your narcotic load is equivalent to breathing air at 30.0 meters.

Abs. Pressure

4.00 bar

ppN₂

3.16 bar

ppO₂

0.84 bar

MOD

57 mt

@ 1.4 bar

Narcotic Partial Pressure

4.00 bar

Total narcotic load = ppN₂ + ppO₂ at depth. This is the value used to calculate END.

This tool is intended to be used as an informational and educational tool

Trimix diving requires specific certification from a recognised agency (TDI, PADI Tec, IANTD, GUE, or equivalent). Always plan technical dives with a certified instructor or dive guide. Never use this tool as the sole basis for a dive plan.

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Nitrogen Narcosis & Equivalent Narcotic Depth (END) Calculator

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