In the section, Papier Mache Rediscovered By Ronnie Burkett from Proptology Online, the reader is cautioned against putting a styrofoam ball in the oven (Toxic Fumes Alert) and then later in the same paragraph is told that a quick method for removing that same ball from a head is to melt it out with ACETONE. Besides the fact that the acetone itself is toxic, the fumes released by this process are AT LEAST as harmful as those from the oven. As those of us providing information on the web necessarily have to assume the attitude that viewers have zero-knowledge of the topics, it does seem hazardous to recommend such a process without advising precautions such as gloves, a respirator and adequate ventillation. The referenced passage is copied below for your convenience.
The instructions which come with Celluclay recommend oven drying at a relatively low temperature, although both McKinley and Craig boost the heat as high as 300-350 degrees Fahrenheit. It is very important to note, however, that if you have used styrofoam as an armature, you must not put this in the oven, as it will melt the styrofoam and release toxic fumes. This is an absolute no-no! It is best to let the sculpture air-dry for a couple of days, then carefully cut and pick the styrofoam out through the (puppet) neck hole. If you are into instant gratification, both Bob McKinley and I simply pour a bit of acetone (solvent) into the head, which almost instantly dissolves the styrofoam. Be sure it has all evaporated and dried before sticking it in the oven.
Papier Mache Rediscovered By Ronnie Burkett from Proptology Online