Divers have a choice of several types decompression table options. Two of these decompression stations are the Hempleman and Air Table. Both tables have both their benefits and drawbacks. These tables must be used with 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. This theory said that the human body can remove nitrogen in a linear way, not an exponential manner. Decompression tables were created to support this theory and ensure that divers are safe underwater.
Initial diving practices used 'per compartment accounting' to determine nitrogen content. This was a conservative approach. This method compares each compartment gas to a matrix called the 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. 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 tables were a lifesaver for many people. Hempleman worked hard to overcome the "bends" during his tenure as Royal Naval Physiological Laboratory supervisor from 1968 through 1982. Hempleman's research on decompression tables allowed a man to survive for ten hours at depths equivalent to 1,535 feet.
In 1968, Hempleman revised his tables and included a variable ratio of tissue nitrogen tension to ambient pressure. The Navy was initially resistant to Hempleman's changes, but he modified them based on his diving experience. The updated tables were finally adopted by the Navy in 1972.
Hempleman's revised tables of decompression
Hempleman's 1968 revised decompression table for diving was published. These tables have a variable ratio between tissue nitrogen tension and ambient pressure. These tables were not initially liked by the Navy. Hempleman changed the tables to make them more practical and the Navy adopted them in 1972.
In 1908, Haldane published the first table that was based on his model. Haldane was an ambitious self-experimenter who published the first recognised diving tables in 1908. His experimental work included animal experiments and the publication of the first British Admiralty dive table. As a clinical endpoint to decompression sickness, Haldane's suggestions were extensively used.
Hempleman's modified decompression tables
Hempleman changed the decompression tables in 1968 so that they included a variable ratio between tissue nitrogen tension and ambient pressure. The Navy was not happy with the proposed changes and refused to allow them to be implemented. Hempleman had to amend the tables for practical use. Later, these tables were reproduced in metric units. They were adopted by U.S. Navy 1972.
The tables were adopted by the British Royal Navy in 1908 and they were used until the 1950s when they were redesigned due to concern 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.