Instrumentation Changes and MOC — OSHA Letters of Interpretation

ISA asked how its SIS standard relates to PSM. OSHA said ANSI/ISA-S84.01 is a national consensus standard it considers RAGAGEP for safety instrumented systems, though not the only one. SIS are process equipment: the employer must document the codes used (d)(3)(i)(F) and RAGAGEP compliance (d)(3)(ii), have operating procedures for safety systems (f)(1)(iv), and inspect and test them under mechanical integrity (j). The employer is responsible for deciding whether an SIS is needed. An employer that documents and meets S84.01 and the other PSM requirements for SIS is considered in compliance.

OSHA recognized ANSI/ISA-84.00.01-2004, the updated edition of the SIS standard, as a recognized and generally accepted good engineering practice for safety instrumented systems.

Union Carbide asked about the MI equipment list in (j)(1). OSHA said employers may add equipment they consider critical to the list, and that ISA S91.01, which identifies emergency shutdown systems and controls critical to safety, can be used as guidance in deciding which instruments to include.

OSHA said that, except for replacements in kind, management of change applies to changes in maintenance procedures and in equipment test and inspection frequencies, so lengthening a proof-test interval on a safety instrument is a change that needs MOC.