power failure) with each PRD activa

power failure) with each PRD activation being counted separately. Multiple PRDs that function as a system (e.g. toeither handle large relief loads or to minimize the potential for chattering, Safety Valve (SV) and rupture diskcombinations) are to be counted as a single device. Activation of PRDs to be counted as Tier 3 PSEs includes thefollowing:.Safety Valve (SV)- -If activation is known it should be counted. Exclude times when the SV lifts early or leakswhen the pressure is below the SV set point.Rupture Disc- Count each time the disc is replaced excluding regularly scheduled preventive maintenance.- Rupture Pin Device- Count each time a pin is replaced excluding regularly scheduled preventive maintenance.- Deflagration Vent- Count each time the vent must be re-seated excluding regularly scheduled preventivemaintenance.PressureNacuum (PV) Vents (e.g. on tanks)- Count only events in which the PV vent fails to function. This istypically indicated by damage to the tank.7.2.3.3 CalculationThe count of Demands on Safety Systems is typically segregated by system type (e.g. SIS, PRD, and MechanicalTrip). Some Companies may find that a rate of demands per safety system type provides a more useful indicator thana simple count. Tier 3 Demands on Safety Systems may be subcategorized as fllows:number of sIs activations;一number of mechanical trip activations;- number of Tier 3 PRDs directly to atmosphere;number of Tier 3 PRDs to atmosphere via a downstream destructive device.7.2.4 Other LOPC Events7.2.4.1 General