If you try to convert any element into COAL or BCOL, either by typing '!set type [element] coal/bcol' or by using the PROP command, the coal/bcol that you have produced instantly combusts into flame, at a temperature of around 220.
Though it hasn't given me any problems for making saves (yet), it might do so for other users.
That is because COAL with a life of 0 combusts.
When you convert the element the life will be the same as the first element.