Safety Considerations Guide, Tricon v9.0 - Tuv-fs.com

22 General GuidelinesFire and Gas SystemsFire and gas applications typically do not have a safe state and should operatecontinuously to provide protection. The following industry guidelines apply:• If inputs and outputs are energized to mitigate a problem, a PES systemshould detect and alarm open and short circuits in the wiring between thePES and the field devices.• An entire PES system should have redundant power supplies. Also, thepower supplies that are required to activate critical outputs and read safetycriticalinputs should be redundant. All power supplies should be monitoredfor proper operation.• De-energized outputs may be used for normal operation. To initiate actionto mitigate a problem, the outputs are energized. This type of system shouldmonitor the critical output circuits to ensure that they are properlyconnected to the end devices.Tricon Safety Considerations Guide