Various types of decompression tables are available for divers. The Air Table and Hempleman's decompression tables are two such decompression tables. Both tables have their advantages and disadvantages. 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. According to this theory, the human body can eliminate nitrogen in a linear manner rather than at an exponential pace. To accommodate this theory, decompression tables have been created to help divers stay safe and sound 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. 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 table helped save many lives by keeping the Royal Navy at the cutting edge in deep diving technology. During his tenure as Royal Naval Physiological Laboratory superintendent from 1968 to 1982, Hempleman worked to overcome "the bends." Hempleman's research on decompression tables allowed a man to survive for ten hours at depths equivalent to 1,535 feet.
Hempleman updated his tables in 1968 and added a variable ratio between tissue nitrogen tension and ambient pressure. Although he was initially unsuccessful in getting the Navy to adopt his new tables, he made modifications based upon 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 provide a variable ratio in tissue nitrogen tension to ambientpressure. These results were not appreciated by the Navy at first. Hempleman made modifications to the tables for practical reasons and the Navy adopted the new tables in 1972.
In 1908, Haldane's first table model was published. Haldane was an intrepid self-experimenter and published the first recognized diving tables in 1908. His experiments included animal research and the development of the first British Admiralty-approved decompression table. As a clinical endpoint to decompression sickness, Haldane's suggestions were extensively used.
Hempleman's modified depression tables
Hempleman revised decompression charts in 1968 to incorporate a variable ratio for tissue nitrogen tension and ambient press. However, the Navy refused to approve the changes and refused the tables' implementation. This led Hempleman to change the tables for practical purposes. 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, U.S. Navy adopted what are now called C- and R tables. This practice became widespread in the 1980s.