Decompression schedule
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A Decompression Schedule is a series of increasingly shallower decompression stops for (usually) increasing amounts of time that a diver uses to offgas inert gases from the diver' body on the ascent to the surface to reduce the risk of decompression sickness. In a decompression dive, the decompression phase makes up a large part of the time spent underwater (in many cases its longer than the actual time spent a depth).
The depth and duration of each stop is dependent on many factors, primarily the profile of depth and time of the dive, but also the breathing gas mix, the interval since the previous dive and the altitude of the dive site. The diver obtains the depth and duration of each stop from a dive computer, decompression tables or dive planning computer software. A deco diver will typically prepare several decompression schedules to plan for contingencies such as going deeper than planned or spending longer at depth than planned.
An example of a deco schedule
A dive to 130 ft on air for 10 minutes (the No decompression limit (NDL) is 5 minutes)
Waypoint at 130 ft for 10:00 (13) on Air, PPO2 1.036, END 130
Deep Stop at 110 ft for 0:20 (13) on Air, PPO2 0.909, END 110
Deep Stop at 100 ft for 0:20 (14) on Air, PPO2 0.845, END 100
Deep Stop at 90 ft for 0:20 (14) on Air, PPO2 0.782, END 90
Deep Stop at 80 ft for 0:20 (15) on Air, PPO2 0.718, END 80
Deep Stop at 70 ft for 0:20 (15) on Air, PPO2 0.655, END 70
Deep Stop at 60 ft for 0:20 (15) on Air, PPO2 0.591, END 60
Deep Stop at 50 ft for 0:20 (16) on Air, PPO2 0.528, END 50
Deep Stop at 40 ft for 0:20 (16) on Air, PPO2 0.464, END 40
Norm Stop at 20 ft for 4:00 (20) on Air, PPO2 0.337, END 20
TOTAL DECO TIME: 7 minutes.DIVE RUN TIME: 20 minutes.
The "Deep Stops" are a gradient reducing technique to limit bubble formation. The "Norm Stop" is a shallow deco stop.
Typically this dive would be done on a lean nitrox. A deco dive would be longer.
In an accelerated deco schedule, gasses with higher oxygen contents are used to speed up the decompression. This carries with it the risk of oxygen toxicity, therefore situational awareness and depth control are a must.
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