We have an occurrence where a small topsides ESD is reported to be "passing". Leakage rate has not been quantified. Our performance standard requires topsides ESDVs to provide effective isolation of hydrocarbon inventory on demand. Our assurance routine is to ensure valves close within specification time through system wide ESD test or crediting of unplanned ESD. Valve passing is only picked up through operational experience (eg preparing for intrusive work). Typically, we treat performance standard deviations as safety critical corrective work and ensure mitigating measures are in place until work is completed. Question that has been raised is what leakage rate on topsides SDVs should be considered an unacceptable leakage rate? How do other operators treat incidents like these? What standards are there to check the leakage rate?