Let me add that you should be sure the available foam IS polystyrene
'Styrofoam', 'Certi Foam', and 'Foamula R' are some brands.
foam's vapors are more harmful, and may include isocyanates, which you
can apparently become sensitized to at rather low exposure levels.
MSDS for polyurethane foam:
California state information for isocyanates (surprisingly thorough):
Note that, unfortunately, the important part is missing, which is the
AMOUNT of isocyanates in the vapors from foam-cutting...oh well.