Divers can choose from a variety of decompression tables. The Air Table and Hempleman's decompression tables are two such decompression tables. Both tables have their 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. Decompression tables were created to support this theory and ensure that divers are safe underwater.
Originally, diving practitioners relied on 'per compartment' accounting, which is a more conservative approach to determining nitrogen content. This compares the different compartment gases to an M-values matrix. These values are often called 'half-times' by diving professionals, but they are mathematical expressions and not real entities. Air tables that are based on this method tend not to be accurate for long, shallow dives.
Hempleman's decompression table
Val Hempleman's decompression table helped save many lives by keeping the Royal Navy at the cutting edge in deep diving technology. 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. 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 tables of decompression
Hempleman published revised diving decompression tables in 1968. These tables show a variable ratio for tissue nitrogen tension to ambient air pressure. These results were initially not liked by the Navy. However, Hempleman modified them for practical purposes. The Navy adopted the new tables in 1972.
In 1908, Haldane's first table model was published. 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. Haldane's recommendations were widely used as a clinical endpoint for decompression sickness.
Hempleman's modified compression tables
In 1968, Hempleman revised the decompression tables to include a variable ratio of tissue nitrogen tension to ambient pressure. However, the Navy did not approve of the changes and refused to implement the tables. Hempleman decided to alter the tables for practical purposes. 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. The U.S. Navy also began using the C and R tables in the same decade. This practice was popularized in the 1980s.