Set in a stone plinth is what appears to be a giant barrel, seven feet deep and five feet wide. A wooden beam over the barrel carries a rope sling and winding mechanism for lowering peaple into the barrel and getting them out again. The interior of the barrel is covered with thick, hammered silver foil, and there is a lid, also covered in silver foil, which seals the barrel almost - but not quite - perfectly. Around the lip of the barrel, inscribed into the silver foil, is a series of words in a language which resembles Arcane Daemonic Magick - these words dedicate the barrel to Zuvassin, and mean that it undoes the doings of Chaos. To cleanse a victim of Chaos taint, disease, or mutation, the victim is placed inside the barrel, the lid is sealed and the Cleansing Fire of Zuvassin is invoked by a short ritual.
The Cleansing Fire is not gentle. The apparatus is something like a magical microwave oven that causes the stuff of Chaos to overheat and boil away. It might even be able to destroy Warpstone, although no-one has tried this. The more Chaos there is in the victim, the greater the heat and the greater the stress. The heat leaves no physical burns or other marks, but works inwardly, causing a high fever with delerium, aching joints and acute weakness.
The Cleansing Fire causes D6 W (regardless of T, armour or other considerations) for each mutation it burns away. If the Fire is treating a creature or follower of Chaos, such as a Chaos Warrior, Beastman or Harpy, it causes an additional 4D6 W. This additional damage does not apply to members of the cult of the Ancient Allies. Victims taken below zero W must roll on the Sudden Death Critical Hit Table. Survivors gain one Insanity Point for every W point they lose to the Cleansing Fire.
After the Cleansing Fire has taken effect, what is left - be it dead or alive - is completely free of Chaos. Even a Beastman will be completely Human after the Fire has cleansed it.