Usually F&G will not be having a final element (unlike in ESD), except for deluge systems. In O&G industry the final element would be generally a deluge valve (for open areas), where in event of confirmed fire (from a 2ooN input) will send DO to the deluge valve to open and extinguish fire.
In case of closed areas, like substations there will be an output from the fire alarm panel to the fire extinguishing system like Inergen, Co2 (which is outdated now a days) etc.
Please be noted that huge F&G systems in oil & gas industries are SIL 3 and above certified and usually single input will trigger local sounder & beacon (along with alarm on SCADA and matrix fascia) and confirmed input (2ooN) shall take tripping action, as per cause & effect.