Machine Safety

An ongoing discussion of machine guarding topics, including solutions assessments, regulatory compliance, gap analysis, operating efficiencies and cost savings, as well as all relevant safety standards, such as those from NFPA, ANSI, RIA, IEC, ISO and OSHA. About J.B. Titus.

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

September 02, 2009


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



For more than 30 years, J.B. Titus has advised a wide range of clients on machine functional safety solutions, including Johnson + Johnson, Siemens, General Motors, Disney, Rockwell Automation, Bridgestone Firestone, and Samsung Heavy Industries. He holds a Bachelor of Business Administration degree from Oklahoma University in industrial management and an MBA from Case Western Reserve University in marketing and finance. He is a professional member of the American Society of Safety Engineers and is OSHA-certified in machine guarding. Titus is also TUV-certified as a Functional Safety Expert and serves on several American National Standards Institute, National Fire Protection Association, and National Electrical Manufacturers Association national safety and health standards committees. Reach him at jb(at)jbtitus.com and via www.jbtitus.com.