I can't be sure, but be sure to check other forums and cross referance.
We were allowed to cut styrene. But there was a list of banned materials.
I know for sure that PVC and Vinyl were two of them. The off gassing was
Chlorine gas, or Cyanide gas, from things like PVC, and Polycarbonate.
Both gas may not be cleared using your indoor filters, and are certainly deadly.
If you are unsure of about what you are cutting, don't cut it.
I know of one other machine that was killed within a year, because the
shop thought they had an approved plastic.
[edit]
Here we go...
http://atxhs.org/wiki/Laser_Cutter_Materials There may be confusion between polystyrene foam and sheet styrene plastic.
I know many shops that cut foam core or Gator board. the foam is a Polystyene sandwiched
between paper or plastic. Other than a huge undercut, melting foam, the foam core cuts okay.
The shop I used did have a fire in the Epilog, caused by someone cutting cardboard.
They had walked away from the machine and "let it do it's thing".
I have seen balsa wood catch an ember, and seen that ember burn across the board fueled
by the exhaust fan, while the laser cut elsewhere on the pattern.
We were told after the fire, by no means leave the machine unattended.