On January 18 at 10:30 hrs. the communications system failed to work from the main control room to other areas of the plant at the time of establishing contact. This emergency was declared as a 'non usual event'. At 10:45 hrs the emergency notifier was given notice by the loud speakers and CNSNS was also informed by phone, extension 300, of pere at Cat (Technical Support Center). At 12:45 hrs. phone extension 243 was back in operative condition, therefore ending the event. Initiator: None; frequency: possible; availability: adequate. Original classification: 1 from Table 1 column 2C of the INES users' manual. Due to lack of communication the safety of the plant could have been involved.