Slightly longer answer: 60 ft/min was never based on anything more than a compromise between 10 ft/min (the rate of cranking up a hard-hat diver) and 100 ft/min (what the "new" scuba divers wanted to do). It was never science-based, but then became embedded in the tables being developed because the ascent rate is part of the deco algorithm. PADI has never ever wanted to say it was ever wrong about anything, even if new information arises, so it still maintains 60 ft/min as a max rate, but then says do what your computer says...which is almost always 30. We now know that -- especially near the surface -- 60 ft/min is stupid. From deep to mid depths, 60 is more tolerable. Physiologically, it ahs to do with the rate at which pressure is released on the body as you ascend, do 60 ft/min from 130-60 ft is not much of a fractional pressure drop, whereas 60 ft/min from 30 ft to the surface is a very large fractional pressure drop. One BIG reason that safety stops have become the standard is because it slows you down.
From
DAN:
Ascent Rates: A Quick History
Historical guidelines as to rates of ascent are pertinent. In the 19th century, for example, the French physiologist Paul Bert in 1878 quoted rates of 3 feet per minute and the English physiologist John Scott Haldane in 1907 recommended ascent rates between 5 and 30 feet (1.5 and 9 meters) per minute. From 1920-1957, rates of 25 feet (7.5 meters) per minute were recommended.
Then in 1958, during the production of the U.S. Navy Diving Manual, the rate of ascent to be proposed came under review. Cdr. Francis Douglas Fane of the U.S. Navy West Coast Underwater Demolition Team wanted rates for his frogmen of 100 feet (30 meters) per minute or faster. The hardhat divers, on the other hand, considered this impractical for the heavily suited divers who were used to coming up a line at 10 feet (3 meters) per minute. Thus, a compromise was reached at 60 feet (18 meters) per minute, which was also a convenient 1 foot per second.
So from 1957 until 1993 the U.S. Navy tables have consistently advocated an ascent rate of 60 feet per minute, based on this purely empirical decision, with many recreational diving tables and even early computers following suit. In recent years this has been slowed to 30 feet per minute with a recommended safety stop for three to five minutes at 15-20 feet (4.5-6 meters). However, this still brings the diver quite rapidly to the surface, often after some 30-60 minutes at depth.
