"It's an activation key used to operate a crane."
— Item examination
This key is found in the same room where the empty extinguisher is refilled. To retrieve it, the tank it's found in has to be emptied; however, a seeker will bust in the tank and attack after picking it up. When the crane is activated, Nosferatu will be lifted out of the ice he's frozen in and his ear ring can be retrieved. The giant spider that follows is entirely an option to combat.