ANSI/ISA standard affects existing SISs

However, S84.01-2004 applies to the mitigation of safety risks and catastrophic environmental events. Other instrumented systems are often installed to mitigate economic or asset risks, but these systems are generally implemented using management systems that are specific to them. In general, a large percentage of the automatically initiated shutdowns are for asset or economic protection. A hazard & risk analysis can be used to identify those functions that are required for safety and to define their functionality and risk reduction requirements. Once the SIF have been defined, the performance of the installed SIF can be compared to the requirements to identify gaps.

Summary
The grandfather clause of S84.01-2004 does not provide an indefinite shield against the requirements of the standard. It provides the essential criteria that should be considered in the evaluation of SIFs that mitigate process risk enabling the process to operate in a safe manner. Good engineering practice, as outlined in ISA TR84.00.04, requires that the following activities be conducted during the evaluation of the applicability of the grandfather clause to an existing SIF:

Determine the risk reduction required for each SIF in the SIS using hazard and risk analysis. Verify that the design and operating basis for the existing SIF delivers the required risk reduction.

Upgrading existing facilities to meet the intent of S84.01-2004 should be accelerated when existing devices are found to no longer meet the required risk reduction. This determination may be made through hazard and risk analysis, test and inspection findings and reports, operation reports of SIS demands and failures, and audits of the performance of personnel and systems against procedures and expectations. In existing facilities, the hazard and risk analysis often serves as the trigger for the periodic reevaluation of protection layer adequacy and conformance to the latest standard.

References:

1. “Process Safety Management of Highly Hazardous Chemicals; Explosives and Blasting Agents,” 29 CFR Part 1910, OSHA, Washington (1992).
2. “Application of Safety Instrumented Systems for the Process Industries,” ANSI/ISA 84.01-1996, Instrumentation, Systems, and Automation (ISA), Research Triangle Park, NC (1996).
3. “Functional Safety: Safety Instrumented Systems for the Process Industry Sector,” International Electrotechnical Commission (IEC), IEC 61511 Geneva, Switzerland (2003).
4. “Functional Safety: Safety Instrumented Systems for the Process Industry Sector,” ANSI/ISA 84.00.01-2004 Parts 1-3 (IEC 61511 mod), Instrumentation, Systems, and Automation (ISA), Research Triangle Park, NC (1996), Research Triangle Park, NC (2004).
5. U.S. Department of Labor, OSHA, Formosa Plastics Corporation, Inspection Number 305893679, Inspection Dates 4/24/2004 through 10/20/2004.
   

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About the Author

Dr. Angela E. Summers, PE, PhD, is president of SIS-TECH Solutions LLC and can be reached at esummers@sis-tech.com.