Divers have many options for decompression tables. Two such tables are the Hempleman's and Air Table decompression table. Each table has its own advantages and disadvantages. These tables must be used with 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. The theory suggested that nitrogen can be eliminated in a linear fashion by the human body, and not at an exponential rate. 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 uses the M-values matrix to compare the various compartment gases. These values are often called 'half-times' by diving professionals, but they are mathematical expressions and not real entities. 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 deep diving technology was saved by the Royal Navy's use of decompression tables. Hempleman's tenure as the Royal Naval Physiological Laboratory Superintendent from 1968 to82 saw him work to overcome "the bends." Hempleman's research into decompression tables enabled a man to survive for ten hour at a depth equivalent of 1,535 feet.
Hempleman updated his tables in 1968 and added a variable ratio between tissue nitrogen tension and ambient pressure. 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 table of decompression
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 based on Haldane's model was published in 1908. In 1908, Haldane published the first known diving tables. He was an adventurous self-experimenter. 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 depression tables
In 1968, Hempleman revised the decompression tables to include a variable ratio of tissue nitrogen tension to ambient pressure. However, the Navy rejected the changes and refused permission to implement them. Hempleman had to amend the tables for practical use. Later, these tables were reproduced in metric units. They were adopted by U.S. Navy 1972.
In 1908, the British Royal Navy adopted these tables and used them until the 1950s. They were then revised due to concerns about being 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.