You ask the weirdest questions.
Ok quick lesson in PSU etiquette.
1> They are short circuit protected. A short will shut the PSU completely down.
2> They are overload protected. If the draw off any leg exceeds beyond a preset point, the voltage regulator for that leg will over heat and go in to thermal shut down. When it cools down, if not damaged, it will come back to life. A cold start on the PSU is required.
3> Some PSU's come with thermal or solid state or glass fuses. Solid state and glass fuses have to be replaced. Thermal fuses self reset.
Odds of a PSU or any other part of a computer catching fire are slim and none.
However...
Flipping the power input switch to 115vac and plugging it in to 220vac will put on one hell of a fireworks show as the windings in the transformer go blooey.