Is it common practice to use Safety Instrumented Systems (SIS) i.e., SIL-1 or higher rated systems on hydrogen systems?

While not required, Safety Instrumented Systems with a specific SIL rating are often used on hydrogen systems. The hazard analysis provides guidance as to whether a SIL rating for a given exposure is required and at what level. The SIL level depends on the probability and consequence of occurrence of a given hazard. Hydrogen equipment may be provided with different SIL levels within the same overall system.