Divers can choose from a variety of decompression tables. There are two types of decompression tables: the Air Table and Hempleman's. Both tables have their advantages and disadvantages. These tables should be used with care and a diving guide should always be used in conjunction with the decompression table.
Air Table decompression tables
The first decompression tables were created by the Navy's Naval Experimental Diving Unit in 1930. It was based on an original theory. According to this theory, the human body can eliminate nitrogen in a linear manner rather than at an exponential pace. This theory was reflected in decompression tables, which were designed to aid divers staying safe underwater.
In the beginning, divers used 'per-compartment' accounting to determine nitrogen content. This method compares each compartment gas to a matrix called the M-values. Diving practitioners often refer to these values as 'half-times', though it is important to note that they are only mathematical expressions, not real entities. This method is conservative in the short-term and may not be correct for deep, long dives.
Hempleman's Decompression Tables
Val Hempleman’s deep diving technology was saved by the Royal Navy's use of decompression tables. Hempleman was the Royal Naval Physiological Laboratory's superintendent between 1968 and 1982. He worked tirelessly to "overcome the bends." His research on decompression table helped a man survive ten hours at the depth of 1,535 feet.
Hempleman updated his tables in 1968 and added a variable ratio between tissue nitrogen tension and ambient pressure. After initially being unable to convince the Navy to adopt the tables, Hempleman made modifications based in his diving experiences. In 1972, the Navy adopted the updated tables.
Hempleman's revised table of decompression
Hempleman revised the decompression tables for diving in 1968. These tables allow for a variable ratio of tissue tension to ambient pressure. These tables were not initially liked by the Navy. Hempleman changed the tables to make them more practical and the Navy adopted them in 1972.
In 1908, Haldane published the first table that was based on his model. Haldane was an independent experimenter who published the first diving tables in 1908. His experiments also included animal studies and the design of the British Admiralty's first decompression tables. The clinical endpoint of decompression sickness was widely used by Haldane.
Hempleman's modified despression tables
In 1968, Hempleman revised the decompression tables to include a variable ratio of tissue nitrogen tension to ambient pressure. However, the Navy rejected the changes and refused permission to implement them. Hempleman was able to modify the tables for practical reasons. These tables were later reprinted using metric units, and adopted by U.S. Navy in 1972.
The British Royal Navy adopted the tables in 1908 and continued using them until the 1950s, when they were revised because of concerns that they were too conservative. In the same decade, the U.S. Navy began using what are now known as C and R tables, and this practice became common in the 1980s.