Divers have a choice of several types decompression table options. Two such tables are the Hempleman's and Air Table decompression table. Both tables have their own benefits and drawbacks. These tables must be used with care.
Air Table decompression tables
The 1930's saw the development of decompression table standards. This was when the Naval Experimental Diving Unit created the first tables that were standardized on a theory. This theory stated that the human body is able to eliminate nitrogen in a linear fashion, rather than at an exponential rate. To accommodate this theory, decompression tables have been created to help divers stay safe and sound underwater.
In the beginning, divers used 'per-compartment' accounting to determine nitrogen content. This method uses the M-values matrix to compare the various compartment gases. Diving practitioners often refer to these values as 'half-times', though it is important to note that they are only mathematical expressions, 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. His research on the decompression tables was instrumental in helping a man survive for ten consecutive hours at a depth of 1.535 feet.
Hempleman revised his tables in 1968. He added a variable rate of tissue tension to ambient pressure. The Navy was initially resistant to Hempleman's changes, but he modified them based on his diving experience. The Navy finally adopted the revised tables in 1972.
Hempleman's revised table of decompression
Hempleman's 1968 revised decompression table for diving was published. These tables show a variable ratio for tissue nitrogen tension to ambient air pressure. Although initially the Navy didn't like the results, Hempleman modified these tables for practical purposes. In 1972, the Navy adopted the new tables.
The 1908 publication of the first Haldane-based table was a result. Haldane, an avid self-experimenter, published the first officially recognized diving tables in 1908. His experiments also included animal studies and the design of the British Admiralty's first decompression tables. As a clinical endpoint to decompression sickness, Haldane's suggestions were extensively used.
Hempleman's modified decompression tables
In 1968, Hempleman revised the decompression tables to include a variable ratio of tissue nitrogen tension to ambient pressure. The Navy opposed the changes and refused implementation of the tables. Hempleman changed the tables to make them more practical. In 1972, the U.S. Navy adopted these tables in metric units.
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 began using what are now known as C and R tables, and this practice became common in the 1980s.