The CPUs do not give the OS a command to shut down, they just shut down. On some motherboards, the CPUs communicate with the BIOS to control fan speeds, and in some cases (most notably, notebook motherboards) with the bus clocks to toggle down in speed to lower temps.
In any case, the idea is the same, self-preservation - to prevent the CPUs from burning up. And there are Windows based hardware monitoring programs that can be used to prevent heat related damage too but the real protection comes comes from within the CPU itself, and with its communication with the motherboard.
So in theory - a CPU should never burn it, it should shut itself down before that happens. But it assumes the CPUs protection feature is working properly. It also assume normal clocking.
About the general heats, and keeping fans at low noise level, it's very much about having your fans placed optionally.
Assuming Titanic meant "optimally", I agree. Generally, as noted before, you want good front to back flow through the case.
I have seen computers inside refrigerators, immersed in liquid nitrogen, and all sorts of other "novelty" setups. There are even
tutorials out there. And generally they work, but generally they are not low-maintenance either.
There are "passive" (no fans) cooling systems for CPUs, graphics cards, PC cases used often with HTPCs (home theater PCs) where any fan noise at all is totally unacceptable. There are also whole websites dedicated to
Quiet PCs and
Silent PCs - if really interested.
