Grandfathering, it's not about being old, it's about being safe

摘要

The ANSI/ISA 84.00.01-2004 contains a grandfather clause which allows users to keep their existing Safety Instrumented Systems (SIS), which were designed to previous Good Engineering Practices, without having to upgrade the SIS to the current standard. The grandfather clause is only a sentence; the basic premise is that you have to document that you have evaluated the SIS and have determined that the SIS ensures the process will operate in a safe manner. This paper presents the method one company has used for grand fathering their SIS and the factors they considered in evaluating whether an existing SIS met ANSI/ISA 84.00.01-2004 and OSHA 1910.119 requirements. These factors include: Does the SIS have the proper classification? Does the SIS design provide the proper risk reduction? Is the testing frequency appropriate to ensure the SIS integrity? The method also outlines the types of modifications to the SIS that would negate the grandfather clause and require that the SIS be upgraded to the new standard. Since the grandfather clause only covers the design of the SIS, the grand fathered SIS must still follow the management practices in ANSI/ISA 84.00.01-2004.