An imaging device has a fuser assembly and a removably insertable cartridge with an activation device. The fuser assembly has a fusing nip that heats during use. A shutter moves between a fully opened and fully closed position to allow or block access to the fusing nip. A frame has an opening to allow passage of the activation device of the cartridge. During use, the shutter blocks access to the fusing nip until the activation device of the cartridge passes through the opening of the frame and contacts a corresponding activation surface, whereby the shutter begins opening and travels through a range of movement until reaching the fully opened position when the cartridge is fully inserted into the imaging device. Removal of the cartridge reverses the action of the shutter.