(under subclass 21) Subject matter having an enclosure which is sealed and a fluid within the enclosure and wherein the means to disconnect the filament from its source of electrical energy etc. includes a switch and wherein the enclosure, the fluid and the switch are so interrelated that a break in the enclosure either (1) changes the amount of fluid in the enclosure to open the switch, or (2) changes the pressure of the fluid in the enclosure to open the switch and thus open the circuit to the filament.
