How does emerson define SIS requirements for valves? From what I have seen the general consensus is that the "final element" is rated to IEC 61508 standard. Where the "final element" notation stops is where I am having the issue. We have pneumatic shut off valves going back to the SIS system. The solenoid valve that controls air to the actuator has an IEC 61508 certification but I cannot find the same certification on any valve or actuator. Is there a comparable ISO standard that the mechanical elements follow or am I not looking hard enough for IEC 61508 valves and actuators?