Love those ceiling parts....very retro
Are they indeed plastic ? I noticed you had a broken piece. Please try to set that one on fire somewhere outside and see what happens (will make a cool episode).
If you hold a flame to it it could smoke, but once you remove the flame it should extinguish by itself. Then it's safe (enough)

If the thing ablazes......I wouldn't use them. Maybe you can use some stuff to make them fire-safe...
Seriously....IF there will ever be a fire you don't want plastic to burn and melt and rain down on you..let alone the poisonous fumes they produce......and in the 70's rules weren't so tight about this....oh and talking about 70's....there might be asbestos in these elements to _make_ them fire-safe.....
Sorry fire safety is my profession
