The Shutters Impervious to Ectoplasm is a security measure against ghosts incorporated into the Firehouse.
When the Ghostbusters discovered they had a Copycat running wild in the Firehouse, Egon decided it would be best to lock up so it can't escape the Firehouse. After Egon activated the shutters with a remote control, special shutters sealed up the Firehouse. The bars were said to be impervious to ectoplasm. 
- ↑ Egon Spengler (2009). The Real Ghostbusters - "The Copycat" (1987) (DVD ts. 12:11-12:13). Time Life Entertainment. Egon says: "I installed shutters impervious to Ectoplasm throughout the Firehouse."