These telephones are of Intrinsically Safe construction. They can be used in hazardous areas and allow to connect to the telephones in the safety areas, shown in the layout drawing shown on the previous “Marine Battery-less Telephone”. IS Barrier shall be equipped intermediate for safety connection between two areas (Marine battery less telephones and Marine intrinsically safe construction battery less telephones). This system is roughly classified into two systems; Direct Telephone and Selective (12/24 stations) Telephone. As they do not have devices to tell the reception, other devices such as Air horn, Whistle, and/or Beacon should be equipped. The authentication of the IECEx has acquired. IECEx Certificate No. : IECEx TIIS 16.0003X Ex Protection : Exia II BT4 Ga Ta=55℃