How does Saul handle decompression dives or dives that overstay the allowable no-decompression limit (for the chosen level of probability of DCS) ?  I haven’t previously been discussing decompression because I’ve been focussing on recreational diving.  Recreational diving and decompression diving are handled somewhat separately by SAUL, for reasons outlined below.  When SAUL goes into dive computers, it will handle both recreational and decompression diving  (unless a manufacturer wishes to limit it to recreational).  The reason they are handled separately, is that the algorithm was calibrated separately for each type.

Before the dive, along with choosing the probability level for DCS, the diver will select “recreational” or “decompression”.   Neither of these choices can be changed during the dive.

Recreational

SAUL’s recreational algorithm does not specifically allow for decompression diving.  On the other hand, unlike other recreational dive computers, SAUL will not lock you out even if you exceed your chosen probability level.  It will continue to update and show you your probability of DCS.  You will see some improvement in  probability with a longer safety stop.   At all stops, whether safety or decompression, the greatest benefit is achieved in the earliest part of the stop.  While benefit continues to accrue throughout the duration of the stop, it does so at an increasingly slower pace.  Obviously, the real problem with trying to significantly decompress on dives planned as  recreational is that you wouldn’t have sufficient air remaining to manage it.

Decompression

Decompression dives work much the same way as recreational dives except for the stop.  Thus, before starting the decompression dive, the diver would input their maximum acceptable risk, and would input the fact that the dive is to be a decompression dive. (The latter tells the computer to use a decompression diving-based calibration for the underlying model). Then during the dive, the dive computer, every few seconds, tells the diver how much time is left at the depth the diver is at, so as to ultimately ascend with a total risk (ascent risk + risk at the surface) that doesn’t exceed the allowed risk (again, exactly as in no-decompression diving). When its time to come up, the dive computer tells the diver how much time to spend at specified stop depths, so as to surface within the acceptable inputted risk.

Generally, the stop depths for decompression diving start at a deeper 1st stop (e.g. 25 or 30 fsw, rather than 15 fsw), relative to no-decompression diving.  Obviously, less time is needed when on nitrox than when on air, for the same level of risk. Also, of course, the total time spent at all the decompression stops will, in decompression diving,  be considerably greater than the 2-5 minutes typical for no-decompression diving.

SAUL has been calibrated for use in air decompression diving, assuming a maximum of 1 dive per 24 hour period. It will also become available, hopefully in the not too distant future, for use in trimix decompression diving using rebreathers.