Divers can choose from several different types of decompression plates. The Air Table and Hempleman's decompression tables are two such decompression tables. Each table has its advantages 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 have been developed since the 1930s, when the Navy's Naval Experimental Diving Unit first created standardized tables that were based on a theory. The theory suggested that nitrogen can be eliminated in a linear fashion by the human body, and not at an exponential rate. Therefore, decompression plates were created to accommodate this theory. They also help divers remain safe underwater.
Original diving professionals used "per compartment" accounting as a method to determine nitrogen contents. This method uses the M-values matrix to compare the various compartment gases. 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 tables
Val Hempleman's decompression tables helped the Royal Navy stay on the cutting edge of deep diving technology and saved many lives. During his tenure as Royal Naval Physiological Laboratory superintendent from 1968 to 1982, Hempleman worked 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. He was initially unable get the Navy adopt the new tables but modified them based his diving experience. The Navy adopted the updated tables in 1972.
Hempleman's revised table of decompression
Hempleman revised the decompression tables for diving in 1968. These tables allow for a variable ratio of tissue tension to 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 independent experimenter who published the first diving tables in 1908. His experiments included animal experiments as well as the creation of the first British Admiralty decompression table. Haldane's recommendations were widely used as a clinical endpoint for decompression sickness.
Hempleman's modified Decompression Tables
Hempleman revised decompression charts in 1968 to incorporate a variable ratio for tissue nitrogen tension and ambient press. The Navy opposed the changes and refused implementation of the tables. Hempleman decided to alter the tables for practical purposes. These tables were later reproduced in metric units and were adopted by the U.S. Navy in 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. The U.S. Navy also began using the C and R tables in the same decade. This practice was popularized in the 1980s.