Various types of decompression tables are available for divers. Two such tables are the Hempleman's and Air Table decompression table. Both tables have both their benefits and drawbacks. These tables should not be used without care.
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 suggested that the human body could eliminate nitrogen in an exponential fashion. 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 sometimes called "half-times" by diving practitioners. However, it is important that these numbers are not real entities and only mathematical expressions. The air tables based upon this method are generally conservative and may not work well 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's tenure as the Royal Naval Physiological Laboratory Superintendent from 1968 to82 saw him work to overcome "the bends." His research on the decompression tables was instrumental in helping a man survive for ten consecutive hours at a depth of 1.535 feet.
Hempleman changed his tables to include a variable ratio for tissue nitrogen tension and ambient press in 1968. The Navy was initially resistant to Hempleman's changes, but he modified them based on his diving experience. The Navy adopted the updated tables in 1972.
Hempleman's revised Decompression Tables
In 1968, Hempleman published revised decompression tables for diving. These tables show a variable ratio for tissue nitrogen tension to ambient air 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.
The first table to be based on Haldane’s model was published by Haldane in 1908. Haldane, an avid self-experimenter, published the first officially recognized diving tables in 1908. His experimental work included animal experiments and the publication of the first British Admiralty dive table. As a clinical endpoint to decompression sickness, Haldane's suggestions were extensively used.
Hempleman's modified Decompression 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. Hempleman had to amend the tables for practical use. 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 back in 1908 and used them until 1950s. In the same decade the U.S. Navy used what are now known C andR tables. This practice became popular in the 1980s.