Divers have many options for decompression tables. There are two types of decompression tables: the Air Table and Hempleman's. Both tables have their own benefits and drawbacks. These tables must be used with 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. 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.
Originally, diving practitioners relied on 'per compartment' accounting, which is a more conservative approach to determining nitrogen content. This method compares different compartment gases to a matrix known as M-values. These values are often called 'half-times' by diving professionals, but they are mathematical expressions and not real entities. These air tables are conservative for short-term dives and can be inaccurate for shallower, longer 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. 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. After initially being unable to convince the Navy to adopt the tables, Hempleman made modifications based in his diving experiences. In 1972, the Navy adopted the updated tables.
Hempleman's revised decompression tables
Hempleman revised the decompression tables for diving in 1968. These tables have a variable ratio between tissue nitrogen tension and ambient 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 included animal experiments as well as the creation of the first British Admiralty decompression table. Haldane’s clinical guidelines were widely adopted as a guideline for decompression sick.
Hempleman's modified compression tables
Hempleman updated the decompression table to include a variable rate of tissue nitrogen tension relative to ambient pressure in 1968. However, the Navy rejected the changes and refused permission to implement them. Hempleman had to amend the tables for practical use. These tables were later reproduced in metric units and were adopted by the U.S. Navy in 1972.
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. The U.S. Navy also began using the C and R tables in the same decade. This practice was popularized in the 1980s.