Various types of decompression tables are available for divers. Two of these decompression stations are the Hempleman and Air Table. Each table has its advantages and drawbacks. These tables should not be used without care.
Air Table decompression tables
The development of decompression tables dates back to the 1930's when the Navy's Naval Experimental Diving Unit developed the first standardized tables 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. As a result, decompression tables were developed to accommodate this theory and help divers stay 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 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 tables
Val Hempleman’s deep diving technology was saved by the Royal Navy's use of decompression tables. 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. He was initially unable get the Navy adopt the new tables but modified them based 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 allow for a variable ratio of tissue tension to ambient pressure. 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.
The 1908 publication of the first Haldane-based table was a result. Haldane was an intrepid self-experimenter and published the first recognized diving tables in 1908. His experiments also included animal studies and the design of the British Admiralty's first decompression tables. Haldane's recommendations were widely used as a clinical endpoint for decompression sickness.
Hempleman's modified depression tables
Hempleman revised decompression charts in 1968 to incorporate a variable ratio for tissue nitrogen tension and ambient press. The Navy was not happy with the proposed changes and refused to allow them to be implemented. Hempleman decided to alter the tables for practical purposes. Later, these tables were reproduced in metric units. They were adopted by U.S. Navy 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 started using what is now called C and R table in the same decade. This practice became more common in 1980s.