I don't believe it is possible for someone to just be walking down the road and all the sudden burst into flames, however it is possible for a person to spontaneously combust if an outside flammable element is introduced. If this material were to catch flame nearby a person the person can burn up quick by igniting that person's human fat.
Phoenix's burst into flames when they are about to be reborn. When the fire goes out a chick emerges from the ashes. The bird burst into flames because it was getting old.
It bursted into flames in the year 1937
You burst into flames :(
The bunny burst into flames.
Moses
Diamond can disintegrate if heated enough and will give off carbon dioxide on water and disappear Any of the alkaline metals will burst into flames
he danced until his heart burst into flames
Salt is not flammable.
gas
It will burst into flames.
Phosphurus
becasue that is impossible