Here is a brief rundown of how much time you need to wait at each depth
to avoid decompression sickness. Before we go on with the explanation let me
add a little disclaimer:
The following data are just a pure abstraction for game purposes. Do not use it for any reallife situation!
In the following table you will find data for different depths (up to 60 meters)
and different time periods (from 15 minutes to 3 hours). In order to define how
much a character needs to wait in order to complete decompression, first find
out the max depth to where he arrives during his dive. Then find out how much
time he spends at the given depth (round at the nearest quarter of hour).
After having selected the duration subtable and the depth row, move to the left
of one row and you will find how long a character has to wait at the
corresponding depth before going up. The procedure is repeated for each depth
"band".
Let's say, as an example, that your PC reaches a depth of 42 meters and remains
there for 25 minutes. You should consult the subtable for 30 minutes and check
the numbers for a stay at 40 meters.
The actual procedure to decompress is to move "up" towards the surface and wait
there for a given number of minutes. In our example, the diver should move to
the 30 meters zone and wait 21 minutes.
After having completed this phase, he will move up to the 20 meters zone and
wait the indicated time (26). After that, he will reach the 10 meters zone, and
after another 31 minutes he will be free to resurface.
Note that the total time required before resurfacing is 21+26+31=78 minutes. A
character is not required to remain motionless during the decompression waiting
phases, so if he has anything useful to do at different depths he can plan
accordingly and carry out some other tasks while waiting.
00:15 
 00:30 
 
00:45 
 01:00 
 
01:15 

01:30 
 
01:45 

02:00 
 
02:15 

02:30 
 
02:45 

03:00 
