... nuclear power plant ,petroleum,chemical plant ,storage and transport industry etc flammable and combustible area .Then user can be ... telephone adopt stainless steel keypad, which contact resistance≤30ohm,life cycle≥2 million,push force 160-200grams,defend grade is ... dB enviroment .2.4 Hook adopts magnetic induction switch, life cycle ≥500 thousand.Increased safety terminal compartment, to ensure that ...