Divers have many options for decompression tables. Two such tables are the Hempleman's and Air Table decompression table. Both tables have both their benefits and drawbacks. These tables should not be used without care.
Air Table decompression tables
The first decompression tables were created by the Navy's Naval Experimental Diving Unit in 1930. It was based on an original 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.
Initial diving practices used 'per compartment accounting' to determine nitrogen content. This was a conservative approach. 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. The air tables based upon this method are generally conservative and may not work well for long, shallow 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. Hempleman worked hard to overcome the "bends" during his tenure as Royal Naval Physiological Laboratory supervisor from 1968 through 1982. Hempleman's research into decompression tables enabled a man to survive for ten hour at a depth equivalent of 1,535 feet.
Hempleman changed his tables to include a variable ratio for tissue nitrogen tension and ambient press in 1968. After initially being unable to convince the Navy to adopt the tables, Hempleman made modifications based in his diving experiences. The Navy adopted the updated tables in 1972.
Hempleman's revised tables of decompression
Hempleman revised the decompression tables for diving in 1968. These tables provide a variable ratio in tissue nitrogen tension to ambientpressure. 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 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 work included animal experiments and the publication of the first British Admiralty dive table. Haldane's recommendations were widely used as a clinical endpoint for decompression sickness.
Hempleman's modified depression tables
Hempleman updated the decompression table to include a variable rate of tissue nitrogen tension relative to ambient pressure in 1968. 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, the U.S. Navy began using what are now known as C and R tables, and this practice became common in the 1980s.