1.intrinsic safety telephone, with explosion-proof and safety certificate, 2.best quality ,suitable to coal mine underground ... pollution;2) The material of cover is static-free, with features of waterproof, dustproof, anticorrosion and the protection degree IP54 ... pressure: 80kPa~106kPa;4) noise: ≤75dB;5) the place with explosive mixture, but without corrosion gas for insulation ;Technical Data1 ...