Relevant SIL Certification

Relevant SIL Certification

Why It Matters:

It is important to understand what SIL certification means – and what it does not mean. SIL (Safety Integrity Level) ratings were established to define a metric for evaluating a system’s level of operational reliability with regard to safety, as defined by IEC 61508. As it ap­plies to machine monitoring systems, a SIL rating refers to the probability of failure on demand of the protec­tion system. A key point to remember is that SIL ratings have nothing to do with monitoring precision, which is represented by false trips and missed detects. Keep in mind that, before a SIL-rated safety system comes into play, operators have to determine the ap­propriate SIL rating for the machinery that has to be safety protected. In other words, IEC 61508 is a risk-based stan­dard and, in order to apply it, criteria for the tolerability of risks must be es­tablished for the machine, e.g. a HAZOP study must be carried out (Hazard and Operability).

The Best Approach:

Some marketing phrasing, such as “SIL ready” or “Equates to SIL,” can be puzzling. However, there are two ways to clarify the confusion. First, look for a monitoring system whose vendors provide genuine SIL certificates issued by recognized certi­fication institutions. Keep in mind that the SIL rating must cover not only the safety system itself, but also the inherent com-

ponents in the safety loop from sensor to the ESD (Emergency Shutdown Device). Second, be aware that SIL ratings should not only be high, but relevant to your ap­plication. For instance, SIL certification for monitoring over-speed protection is of no significance to a reciprocating compres­sor user, but a rating for a safety system that performs segmented RMS vibration analyses may be significant for your ma­chine. You can expect a protection system with specialized capabilities for reciprocat­ing machinery to be rated as high as SIL 2.

Leave a Reply

Your email address will not be published. Required fields are marked *