What's UP With SIL, Cat and Now PL? Safety Integrity Levels, Categories, and Performance Levels of Machine Safety


We all know by now about safety rated devices according to SIL(safety integrity level) and Cat(category). Recently, a new term has emerged from Europe via ISO 13849-1; 2006 introducing PL (performance level). Most everyone agrees that both SIL and PL are hazard ratings that are quantitatively derived and can be directly related. Cat is a qualitatively derived hazard rating and is not easily directly related to either SIL or PL ratings. It seems that many suppliers of safety rated products are converting from SIL and Cat ratings to SIL and PL ratings and possibly dropping the Cat rating all together. Does this shift in safety ratings actually create a new problem?

Take for example a manufacturer that recently started the required risk assessment process for their manufacturing machinery that identifies hazard levels according to categories. How will that manufacturer retrofit SIL and PL rated safety devices to their machine and fully satisfy the mitigation documentation requirements for hazards identified as Cat levels?

Does anyone have an answer?

Has anyone seen a supplier with a correlation chart or procedure?

Will a SIL 2 & PL d safety rated device satisfy a Cat 4 hazard?

It’s beginning to look like a great opportunity for consultants, right?

Posted by J.B. Titus on September 11, 2009

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