Various types of decompression tables are available for divers. The Air Table and Hempleman's decompression tables are two such decompression tables. Each table has its own 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
Decompression tables were developed in the 1930's by the Navy's Naval Experimental Diving Unit. They created the first standardised tables based upon a theory. This theory said that the human body can remove nitrogen in a linear way, not an exponential manner. Decompression tables were created to support this theory and ensure that divers are safe underwater.
Initial diving practices used 'per compartment accounting' to determine nitrogen content. This was a conservative approach. 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 Decompression Tables
Val Hempleman's deep diving tables saved many lives and helped the Royal Navy remain at the forefront of deep diving technology. Hempleman worked hard to overcome the "bends" during his tenure as Royal Naval Physiological Laboratory supervisor from 1968 through 1982. Hempleman's research on decompression tables allowed a man to survive for ten hours at depths equivalent to 1,535 feet.
Hempleman changed his tables to include a variable ratio for tissue nitrogen tension and ambient press in 1968. He was initially unable to get the Navy to adopt the new tables, but made modifications based on his practical diving experience. The Navy adopted the updated tables in 1972.
Hempleman's revised Decompression Tables
Hempleman's 1968 revised decompression table for diving was published. These tables provide a variable ratio in tissue nitrogen tension to ambientpressure. 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 1908 publication of the first Haldane-based table was a result. 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. The clinical endpoint of decompression sickness was widely used by Haldane.
Hempleman's modified compression tables
Hempleman modified the decompression tables in 1968 to include a variable proportion of tissue nitrogen tension to ambient. The Navy was not happy with the proposed changes and refused to allow them to be implemented. This led Hempleman to change the tables for practical purposes. Later, these tables were reprinted in metric units and adopted by the U.S. Navy on February 2, 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.