With the 92FS was introduced a "passive" safety as for request of the U.S. federal programme (during the trails that determined the M9 to replace the 1911 A1).
In fact in three of these Beretta pistols that were being tested by the Navy Seals (using, by mistake, +P ammos), the slide broke and the rear part was thrown back hitting the shooter.
Lately was officially recognized that this inconvenient had been caused by a wrong lot of "hyper-charged" type M882 9mm cartridges that showed dangerous over-pressures.
In a few words the slide of the FS version features a mechanical safety that, in case of rupture of the slide, can intercept the rear part of it on the frame to avoid injuries to the shooter.
Forgive me if I am not enough clear but unluckily technical english is not so easy to me...