05-30-11: Tripperall (larger) power amps have output protection circuitry ( that kicks in if there is unusually high DC offset) + thermal shut-down circuitry that cuts off the output power stage if the heatsink temp goes too high (this is often monitored by transistors attached directly to the heatsink & the bias running thru these transistors is set to the upper limit of the heatsink temp that the designer thinks is safe) + the power transformer is also designed to provide lower current than the transistor's max so that the transistors always operate in their SOA. All these safety checks (idiot-proofing) ensure that (unless you short the speaker binding posts) the amp will operate safely & within its limits 99% of the time.
No one seems to have mentioned the associated load on the amp and its output stage[s]. As a corollary, one sometimes sees ads that say "drove my Thiels/Apogees/'stats with aplomb". That's all good and well but it would seem that driving the amp to its upper limits might shorten its useful life and perhaps wear it out faster than one would with an easier load. Just wondering...
So, if the amp is driving somebody's Thiels/Apogees/'stats with aplomb then it is doing so within the SOA region of the output transistors (otherwise it'd be shutting down time & again & the owner would not make such a statement).