Forum:Exactly how rare is this?

when i was looking through some articles on this wiki, under the "types of death" category, i saw this:

Fire: If a Sim is on fire for a period of time, he/she will die. It is also possible for a Sim to randomly burst into flames via spontaneous combustion, though that is VERY uncommon.

what i want to know is, how uncommon is it? has it ever happened to you? is there a mod to make it happen more often?