Divers have a choice of several types decompression table options. There are two types of decompression tables: the Air Table and Hempleman's. Both tables have both their benefits and drawbacks. 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. This theory was reflected in decompression tables, which were designed to aid divers staying safe underwater.
Originally, diving practitioners relied on 'per compartment' accounting, which is a more conservative approach to determining nitrogen content. This method compares different compartment gases to a matrix known as M-values. These values are commonly referred to by divers as "half-times", but it is important to remember that they are 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 decompression tables were a lifesaver for many people. Hempleman's tenure as the Royal Naval Physiological Laboratory Superintendent from 1968 to82 saw him work to overcome "the bends." His research on decompression table helped a man survive ten hours at the depth of 1,535 feet.
Hempleman revised his tables in 1968. He added a variable rate of tissue tension to ambient pressure. He was initially unable get the Navy adopt the new tables but modified them based his diving experience. In 1972, the Navy adopted the updated tables.
Hempleman's revised Decompression Tables
Hempleman's 1968 revised decompression table for diving was published. These tables have a variable ratio between tissue nitrogen tension and ambient 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.
The 1908 publication of the first Haldane-based table was a result. Haldane was an ambitious self-experimenter who published the first recognised diving tables in 1908. His experimental studies included animal experiments and the first decompression table for the British Admiralty. As a clinical endpoint to decompression sickness, Haldane's suggestions were extensively used.
Hempleman's modified despression 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 was able to modify the tables for practical reasons. These tables were later reproduced in metric units and were adopted by the U.S. Navy in 1972.
The tables were adopted by the British Royal Navy in 1908 and they were used until the 1950s when they were redesigned due to concern that they were too conservative. In the same decade the U.S. Navy used what are now known C andR tables. This practice became popular in the 1980s.