Until the early 1980s almost all the recreational diving was taught by the standards of U.S. Navy tables. Because the Navy tables are not based on multi-level diving profiles, scientists developed algorithms that take into account changes in nitrogen uptake with continuous changes in depth. These algorithms were mainly theoretical models until the microchip revolution made them accessible and workable in a hand-held computer. When the algorithm is programmed into a computer that also senses depth (a simple depth gauge) and measures time, you have a "dive computer."
Automated decompression monitors were discussed for years before they became reality. The first serious attempt at making a decompression meter was in the mid-fifties by the US Navy. The mechanical device tested was not accurate enough to replace the tables and was abandoned. The first mechanical decompression meter available to the public came out of Italy in 1959. Through the sixties and seventies many companies and military departments worked on various designs with little success. The technology they needed to make their design work would not become widely available until the eighties. In the early eighties the microchip technology became more affordable for many applications. At last the number crunching power necessary for computing decompression in real time was available.
The first commercially available dive computer was the Orca Edge developed by Karl Huggins and Craig Barshinger in 1983. This computer was a multi level computer that used the Haldanian model based on the silent bubble work by Merill Spencer. Since then dive computers have become smaller and more versatile. They are now manufactured by many companies, and incorporate one of several algorithms for calculating nitrogen uptake and elimination.
The first scientific approach to adequate decompression was taken by J.S Haldane in the early 1900. Haldane and his colleagues. Working for the British Admiralty, published their theory in 1908. Haldane's work cantered on the use of half-time theory to describe how tissues accumulate and released nitrogen during diving. Haldane put forward the concept that tissues could be described by time factors, these factors ranging from "fast tissues" to "slow tissues", which controlled the rate at which different tissues took on gases and released them. Tissue half-lives is a method used to describe the time necessary to allow the amount of gas in a particular tissue to change by 50%. Haldane chose 5, 10, 20, 40 and 75 minutes as tissue times based on what was considerate at the time to be the outer limits of diving capabilities. In Haldane's time, bottom time and maximum depths were severely limited by not only decompression, but by the limits of technology. Haldane's theory was based on the following postulates:
Haldane's method had an immediate impact on diving and tunnel workers, as the rate of injury and death was reduced be half. Even so, the limits of Haldane's theory were soon apparent. Haldane himself recognized the need to continue improve his theory as the concept of half-life to describe the amount of nitrogen tolerated by a tissue during decompression was increasingly inaccurate at deeper depths and longer bottom times. Over the years many researchers, both British and American, have worked on expanding and improving Haldane's work. His theory, much reworked by various researchers since 1908, is known as the Neo-Haldanian and is still the basis for modern recreational diving decompression schedules.
Haldane considered the tissues as "parallel" tissues so there was no influence in between the tissues. Only the gas dissolved in the blood was affecting those tissues but they were not affecting each other. Others developed Haldane's ideas over the years. In the mid-1960's US Navy Medical Corps Captain Robert Workman refined the idea of allowable overpressure in tissues, discounting oxygen and considering only inert gasses in the breathing mix, such as nitrogen and helium. Workman's maximum allowable overpressure values (what he called "M-values") were more complex than Haldane's, varying with depth and with tissue type. At around the same time Professor Albert Buhlmann was working on similar research at the University Hospital in Zurich. Buhlmann's research spanned over 30 years and was published as a book, Dekompression - Dekompressionskrankheit in 1983. This book, published in English in 1984, made fairly comprehensive instructions on how to calculate decompression available to a wide audience for the first time and therefore Buhlmann's work became the basis for many dive tables, computers and desktop decompression programs. Three other editions were published, the last in 1995, on which this document is based. See "An explanation Professor A A Buhlmann's ZH-L16 Algorithm by Paul Chapman" in the annexes.
|Updated July 1, 2002 3:56 PM by Vlad Pambucol|