What is an hb pencil? what happens when the h# is increased?

A HB has enchiladas is a pencil is an ordinary pencil. HB is just a scale of the thickness and softness of the pencil.

The answer is all of the above.

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.