Safey stop in PADI's recreational trainin is almost always optional.
Any safety stop is, by definition,
optional. Any stop that imposes a rigid 'ceiling' on the diver is no longer a safety stop - it becomes a deco stop.
PADI confuse the issue by specifying that for certain deep dives/pressure groups the safety stop becomes
mandatory. That is what confuses people, because
you cannot have a mandatory 'safety' stop.
Safety stops are
recommended for one reason: increased conservatism. PADI tables are calculated based upon 3 primary factors (yes, 3). Depth, duration (bottom time) and
ascent rate. Adding a safety stop allows further tolerance to account for individual physiological variances, different diving/water conditions etc. The safety stop also acts as a safeguard to ensure that the 'time to surface' ascent rate (which the tables rely upon) is within the correct parameters. However, the safety stop itself is
not of calculated duration, nor does it factor within the off-gassing equation/model that forms the PADI table.
Safety stops also play an important role in ensuring (novice) diver safety by creating a pause in their ascent, where they can confirm that NDLs haven't been exceeded, moderate their buoyancy, check for overhead boat traffic and prepare for egress from the water etc. In that respect, they have nothing to do with off-gassing... but play a more general role in diver safety.
In contrast, deco stops are
imposed as a necessary part of the off-gassing equation. If you breach the depth ceiling you are at a significantly higher risk of DCS. The mathematics is saying that if you breach the deco stop, you will still be super-saturated beyond the pressure gradient at which bubbles may form.
Now... the PADI 'mandatory' safety stops confuse this differentiation. They aren't a mathematically modelled
requirement for safe off-gassing. They are simply an expression of PADI applying a principle of more rigid conservatism to deeper, more aggressive, dive profiles. Thus we get this wierd scenario of a mandatory-recommended stop. It remains, however, a method of imposing conservatism, rather than a requirement dictated by mathematical bubble modelling.
As such, the mandatory safety stop, should always be treated as a conservatism measure. It should be planned into the dive, but may be aborted if more critical factors subsequently pose safety risks to the diver.
If you blow it, it isn't too bad.
That depends on
how you blow it. Ascent rate is a primary factor in determining the DCI consequences.
If you push the PADI RDP to a point a stop is necesary, then it is actually a deco stop.
Incorrect. The PADI RDP demands a safety stop in 3 instances. If you exceed 30m max depth, if you will end the dive within 3 pressure groups of an NDL... or if you are in the final pressure group/NDL for the dive.
As explained, those instances of mandatory safety stops are still
not deco stops.
A few problems with this so called "in water recompression" for recreation divers:...
There's more than a "few" problems with attempting in-water re-compression. In fact, there are so many potential problems and drawbacks that in-water re-compression is simply
not a viable option unless a considerable amount of logistical and medical planning/preparation has been conducted in advance. It is a
majorundertaking, well beyond the capabilities of any recreational dive charter. If a technical charter/expedition wished to provide re-compression, it'd probably be simpler and more effective to just get a portable hyperbaric chamber on their vessel.
There are already some very informative threads on this subject already. However, as a very basic run-down; here are some considerations:
1) In-water re-compression typically takes
many hours
2) The casualty needs to be delivered with pure O2
3) The casualty needs to be rapidly hydrated
4) The casualty needs medications (immuno-suppressants, anti-inflammatories etc)
5) The casualty needs treatment for shock and/or may lose consciousness
6) The casualty needs continual monitoring, including neurological assessments
7) The casualty needs to be maintained at an optimal temperature
...the list goes on.