Diving is a dynamic activity that requires the diver to constantly react to changes in their environment. Proper planning gives the diver greater flexibility to alter or adapt their dive plan within the constraints of the plan’s maximum depth and maximum bottom time.
Dive Planning Software calculates the diver’s decompression obligations based on a square profile that assumes the diver’s depth does not fluctuate during the dive and that they remain at the planned maximum depth for the entire planned bottom time.
In reality, divers frequently change their depth—for example to adjust for bottom topography, to capture a photo subject from another angle, or to gradually ascend along the length of a wreck. These frequent depth changes are all part of multi-level diving.
Time-to-surface (TTS)—also called ascent time (ASC)—represents the total time required before the diver can surface. It includes deep stops (if applicable), any decompression obligations, and an ascent duration assuming a 10 meters/minute ascent rate. This manual will only use “Time-to_Surface” for convenience.
If their dive computer shows “Time-to-Surface”, the diver can use this information to make their dive more efficient. TTS is dynamic and will increase if the diver:
Remains at depth
Ascends slower than 10 meters per minute
Make a decompression stop deeper than the decompression ceiling
Practical Application
The TTS displayed by the dive computer is neither static nor linear. It is dynamic, and constantly changes as the diver moves in the water column. The TTS readout increases as the diver ventures deeper or stays at a fixed depth for a period of time. It may remain constant or will decrease as the diver ascends into shallower waters.
The diver freely moves up and down in the water column during the bottom stage of the dive, monitoring their TTS to ensure they do not exceed the TTS limit or their minimum gas supply.
As long as the limits are not exceeded, the diver can extend the bottom stage of the dive until their dive computer reaches the TTS limit.
SSI divers can learn all about “Time-to-Surface” and how to plan a dive based on TTS limits by enrolling in the SSI Decompression Diving program.
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