OPC UA Safety supports cyclic and acyclic safety communication.
Most safety functions must react timely on external events, such as an emergency stop button being pressed or a light curtain being interrupted. In these applications, cyclic safety communication is established. That means the SafetyConsumer is executed cyclically, and the time between two consecutive executions is safely bounded. The maximum time between two executions of the SafetyConsumer will contribute to the safety function response time (SFRT).
Some safety functions, such as the transfer of safe configuration data at startup, do not have to react on external events. In this case, it is not required to execute the SafetyConsumer cyclically.