What was the function of a burial mask?

The function of a burial mask was to enable the spirits to recognize the body.

People like the Egyptians believed that if they died faithfully, they would go to the after-world. That's why sometimes they placed food in the tombs too because they thought they would need that in the after world, the burial mask was so that the spirits could recognize the faithful person and take it to the after-world.

Have a nice day! :)

Generally spontaneous human combustion is something that still bewilders some, human combustion happens very rarely and doesn't affect the surrounding areas, so unless you want to set your self on fire, human combustion will remain spontaneous and very rare.