Divers can choose from a variety of decompression tables. Two of these decompression stations are the Hempleman and Air Table. Each table has its advantages and drawbacks. These tables must be used with 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 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.
Divers used to use 'per container' accounting in the beginning. This is a more conservative way of determining nitrogen content. This method compares each compartment gas to a matrix called the 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. Hence, the air tables based on this method tend to be conservative in the short term, and may be incorrect for long, shallow dives.
Hempleman's decompression table
Val Hempleman’s decompression tables were a lifesaver for many people. During his tenure as Royal Naval Physiological Laboratory superintendent from 1968 to 1982, Hempleman worked 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. After initially being unable to convince the Navy to adopt the tables, Hempleman made modifications based in his diving experiences. The updated tables were finally adopted by the Navy in 1972.
Hempleman's revised despression tables
Hempleman revised the decompression tables for diving in 1968. These tables have a variable ratio between tissue nitrogen tension and 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 1908 publication of the first Haldane-based table was a result. Haldane, an avid self-experimenter, published the first officially recognized diving tables in 1908. His experiments also included animal studies and the design of the British Admiralty's first decompression tables. Haldane’s clinical guidelines were widely adopted as a guideline for decompression sick.
Hempleman's modified decompression tables
In 1968, Hempleman revised the decompression tables to include a variable ratio of tissue nitrogen tension to ambient pressure. 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, U.S. Navy adopted what are now called C- and R tables. This practice became widespread in the 1980s.