Divers can choose from several different types of decompression plates. Two such tables are the Hempleman's and Air Table decompression table. Each table has its own advantages and disadvantages. These tables should not be used without care.
Air Table decompression tables
Decompression tables have been developed since the 1930s, when the Navy's Naval Experimental Diving Unit first created standardized tables that were based on a theory. This theory stated that the human body is able to eliminate nitrogen in a linear fashion, rather than at an exponential rate. This theory was reflected in decompression tables, which were designed to aid divers staying safe underwater.
Divers used to use 'per container' accounting in the beginning. This is a more conservative way of determining nitrogen content. This method compares the various compartment gases to a matrix called M-values. These values are often referred to as 'half times' by diving professionals. However, they can only be mathematical expressions, and not real entities. These air tables are conservative for short-term dives and can be inaccurate for shallower, longer dives.
Hempleman's despression tables
Val Hempleman's deep diving tables saved many lives and helped the Royal Navy remain at the forefront of deep diving technology. Hempleman, who was Royal Naval Physiological Laboratory chief from 1968 to 1982 worked to overcome the "bends." Hempleman's research on decompression tables allowed a man to survive for ten hours at depths equivalent to 1,535 feet.
Hempleman revised his tables in 1968. He added a variable rate of tissue tension to ambient pressure. Although he was initially unsuccessful in getting the Navy to adopt his new tables, he made modifications based upon his diving experience. The Navy finally adopted the revised tables in 1972.
Hempleman's revised tables of decompression
Hempleman revised the decompression tables for diving in 1968. These tables include a variable ratio of tissue nitrogen tension to ambient pressure. Although the Navy initially did not like these results, Hempleman modified the tables for practical purposes and the new tables were eventually adopted by the Navy in 1972.
The first table based on Haldane's model was published in 1908. In 1908, Haldane published the first known diving tables. He was an adventurous self-experimenter. His experiments included animal research and the development of the first British Admiralty-approved decompression table. Haldane's recommendations were widely used as a clinical endpoint for decompression sickness.
Hempleman's modified decompression tables
Hempleman changed the decompression tables in 1968 so that they included a variable ratio between tissue nitrogen tension and ambient pressure. The Navy was not happy with the proposed changes and refused to allow them to be implemented. Hempleman had to amend the tables for practical use. These tables were later reprinted using metric units, and adopted by U.S. Navy in 1972.
In 1908, the British Royal Navy adopted these tables and used them until the 1950s. They were then revised due to concerns about being too conservative. In the same decade, U.S. Navy adopted what are now called C- and R tables. This practice became widespread in the 1980s.