The Bühlmann decompression algorithm is a mathematical model (algorithm) of the way in which inert gases enter and leave the human body as the ambient pressure changes. Versions are used to create Bühlmann decompression tables and in personal dive computers to compute no-decompression limits and decompression schedules for dives in real-time. These decompression tables allow divers to plan the depth and duration for dives and the required decompression stops.
Contents
The algorithm was developed by Swiss physician Dr. Albert A. Bühlmann, who did research into decompression theory at the Laboratory of Hyperbaric Physiology at the University Hospital in Zürich, Switzerland. The results of Bühlmann's research that began in 1959 were published in a 1983 German book whose English translation was entitled Decompression-Decompression Sickness. The book was regarded as the most complete public reference on decompression calculations and was used soon after in dive computer algorithms.
The model assumes perfusion limited gas exchange and multiple parallel tissue compartments and uses an inverse exponential model for in-gassing and out-gassing, both of which are assumed to occur in the dissolved phase (without bubble formation).
Principles
Building on the previous work of John Scott Haldane and Robert Workman, and working off funding from Shell Oil Company, Bühlmann designed studies to establish the longest half-times of nitrogen and helium in human tissues. These studies were confirmed by the Capshell experiments in the Mediterranean sea in 1966.
Versions
Several versions of the Bühlmann algorithm have been developed, both by Bühlmann and by later workers. The naming convention used to identify the algorithms is a code starting ZH-L, from Zürich (ZH), limits (L) followed by the number of tissue compartments, and other unique identifiers. For example:
Tables
Max Hahn first used Bühlmann's algorithm to develop dive tables for the Swiss Underwater Sport Association. In 1987, the SAA Bühlmann System was developed by Bob Cole. This system used the dive tables and a set of rules so that people could dive safely and stay below their no-decompression limit. The tables are still used today and are very popular; many dive computers still use the ZHL-8 algorithm and many tables are based on the ZHL-16 algorithm or derivatives. These calculations also include considerations for repetitive and altitude diving.