The EWT Series of THERMOFLEX™ heat detectors for fire alarm systems are Explosion proof, Weather proof, Water-tight and Dust-tight. With its non-metallic diaphragm, the detector can operate normally at low temperatures, making it suitable for non-heated, exposed or chilled spaces including garages, boat decks, engine rooms, tunnels, etc., or in corossive or high humity environments. The Model Number prefix “CR” indicates that the detector is a combination Rate-of-Rise and Fixed Temperature,(often referred to as “Dual-action”), unit.