The present document addresses the requirements for communications between the Authorized Representatives who can be involved in the responses and actions when handling an emergency. Clearly@ the type and number of these Authorized Representatives in a given situation will directly depend upon the nature of the emergency. In the most frequent cases@ only people on duty will have to intervene according to a day-today routine@ but in some cases crisis teams or temporary headquarters will be called and@ according to a plan@ will organize a mass action gathering@ if needed@ the resources of several centres@ or even including in the rescue plan additional levels of administrative authority@ private operators and associations. These new Authorized Representatives will follow instructions or orders from the administrative crisis authority; for example utilities companies (water supply@ transport; energy@ etc.) may have to stop the provision of service or install priority of service schemes or execute a coordinated schedule for the restoration of the infrastructure and the service@ as applicable. It is recognized that the public authorities keep the responsibility of overall management of actions during the duration of the crisis@ establishment of pre-planned scenarios and@ in specific locations@ e.g. tunnels@ underground transports@ plants with high level of risk@ organization of field exercises involving all these Authorized Representatives. The present document describes the functional requirements for communications between the Authorized Representatives involved in the responses and actions when handling an emergency. The level of precision has been chosen to avoid interaction with the specific local@ regional or national organizations and diagrams of relations between Authorized Representatives. It follows from this that adaptations will have to be done when implementing the present document at a local level.