A wizard puts his entire life force into Wizard's Life Fire, which results in his death. However the damage caused by such a spell can be immense. When Wizard Giller gave his life so that Rachel could escape Darken Rahl, he practically destroyed an entire room. Wizard's Life Fire creates a huge explosion of fire.
When a wizard puts his life into the spell, the charred remains that are left behind by it become sorcerer's sand. Depending on the circumstances, this sand can be white or black. White sorcerer's sand tastes bitter and comes from the wizard consuming his life to escape torture or pain while black sorcerer's sand is sweet and comes from the wizard giving his life to save another.