About - Deco Theory

🚧 Work in Progress

This project is a work in progress and has not been reviewed by anyone yet. The content, calculations, and information presented here may contain errors or inaccuracies. Use at your own discretion.

⚠️ Important Disclaimer

This project was created as a personal learning exercise by the author to better understand decompression theory and dive physics. It is an experimental, work-in-progress tool.

No guarantees: There is no guarantee that the information, calculations, or visualizations provided here are correct or complete.
Not for dive planning: This tool must never be used for actual dive planning or any real diving situation. Always rely on certified dive computers, tables, and proper training.
Educational use: This project may be used for educational purposes by Deepblue diving club.

What Is This?

This is an interactive educational resource for divers who want to understand the science behind their dive computers. All visualizations are based on the Bühlmann ZH-L16 decompression model, one of the most widely used algorithms in recreational and technical diving.

The goal is to make abstract concepts like tissue saturation, half-times, and M-values more intuitive through hands-on exploration and visualization.

Algorithm Details

The decompression calculations use the Bühlmann ZH-L16 algorithm with the following parameters and assumptions:

Model Variants

ZH-L16A: Original experimental values, TC1 half-time = 4.0 min
ZH-L16B: Modified for printed tables, TC1 half-time = 5.0 min
ZH-L16C: Modified for dive computers (default), TC1 half-time = 5.0 min

Constants

Surface pressure: 1.0 bar
Water vapor pressure: 0.0627 bar (47 mmHg at 37°C)
Pressure per 10m depth: 1.0 bar (saltwater)
Descent rate: 20 m/min
Ascent rate: 10 m/min
Deco stop increment: 3 m

Gradient Factors

Gradient factors use the Baker pAnchor method:

GF Low applies at the pAnchor depth (first stop)
Linear interpolation from pAnchor to surface (GF High)
Below pAnchor: constant GF Low

Equations

Haldane equation: Tissue loading at constant depth
Schreiner equation: Tissue loading during depth changes
M-value: M = a + P_amb / b
Adjusted M-value: M_adj = P_amb + GF × (M - P_amb)

Validation

The implementation has been validated against:

DecoTengu: Tissue loading matches within 0.02%
Bühlmann printed tables: Deco schedules match within expected tolerance

Note: Our calculations may produce 10-25% shorter deco times than printed tables. This is expected — printed tables include safety margins and round up conservatively. This tool shows the raw algorithm output for educational purposes.

👤 Author

Created by Matej Hron
CMAS I** instructor at Deepblue diving club

matej.hron@gmail.com · LinkedIn

🎓 Expert review

Technical oversight provided by Jiří Hovorka — CMAS/SPČR I3 instructor, trainer of cave diving instructors (ICD3), co-author of SPČR training guidelines — in cooperation with the SPČR Training Commission (Výcviková komise SPČR).

🙏 Acknowledgments

Special thanks to Mark Powell for his excellent book Deco for Divers — the primary inspiration for this project and the resource that made decompression theory finally click.

Thanks also to Jan Jahns for his great book, another valuable learning resource for understanding decompression theory.

📖 References & Sources

Jahns, Jan. (2008). Fyzika. Svaz českých potápěčů, Praha. — Comprehensive overview of diving physics for experienced divers and instructors. Covers essential topics with practical examples from diving. Review on Strany potápěčské
Jahns, Jan. (2008). Podklady k výpočtům dekompresních tabulek Bühlmann/SUSV 1986. 2. vydání. Hlučín, 34 stran. — Mathematical foundations of the Bühlmann ZH-L16 decompression model, including saturation/desaturation equations, M-values, deco stop calculations, and a supplement on ZH-L16B with gradient factors and trimix extensions. Full text (PDF, SPMS)
Powell, Mark. Deco for Divers. — The primary inspiration for this project. An excellent, accessible guide to decompression theory for recreational and technical divers. Highly recommended!
Bühlmann, A.A. (1984). Decompression–Decompression Sickness. Berlin: Springer-Verlag. — The original work describing the ZH-L16 algorithm.
Wikipedia. Bühlmann decompression algorithm — Overview of the algorithm, tissue compartment half-times, and M-values.
Wienke, B.R. Decompression Theory (PDF) — Comprehensive introduction to decompression physics and physiology.
Alveolar Gas Equation: The model accounts for water vapor pressure at body temperature (37°C) = 47 mmHg ≈ 0.0627 bar, which reduces the effective partial pressure of inspired gases. Wikipedia: Alveolar gas equation
Schreiner, H.R. (1971). Safe Limits of Exposure to Increased Pressure. — Derivation of the Schreiner equation for calculating gas loading during linear pressure changes.
Strany potápěčské. stranypotapecske.cz — A comprehensive Czech diving portal and community resource run by Zdeněk Šraier. Features an extensive library of book reviews, educational articles on diving physics and decompression theory, dive site conditions database, equipment reviews, and training materials. An invaluable resource for Czech-speaking divers at all levels.