Abstract: A fire extinguishing device which provides automatic actuation upon exposure to heat is disclosed. The device comprises a vessel composed of a polymeric material and including an opening, a cap for closing the opening after a fire extinguishing medium is charged to the vessel, a valve for pressurizing the vessel after the opening has been closed. The amount of pressure in the vessel and the composition of the fire extinguishing medium and the polymeric material are controlled so that, when the vessel is exposed to heat and/or flame, a portion of the vessel near the heat/flame fails creating a second opening in the vessel, in the vicinity of the portion of the vessel which was exposed to the heat/flame.