Alcoholics going through the DTs, people on drugs, may also see it. It is a plane of total darkness where we must confront the fears we have built within our own minds. Understand that fears have no reality unless we choose to give them reality. As soon as we are able to meet them directly, to face them, they dissipate. This lower level is not for one's punishment, but rather to provide the opportunity to confront and move beyond the negativity created by oneself.
Fire is symbolic of the cleansing and purification of the soul.
The struggle between higher and lower self or what some call God and the Devil causes growth, until finally the negativity or the destructive elements are completely overcome.