Relief and vent system design basis, including the scenarios the system was designed to handle, the design basis flow rates, and the back-pressure assumptions, must be documented and retained as part of PSI. Many facilities have relief systems designed decades ago with design basis documents that have been lost, were never created, or no longer reflect current process conditions. These letters address the documentation obligation, what to do when original design basis is unavailable, and how relief system changes must flow through the MOC process.
What OSHA Has Said
Mar 5, 1998
Relief System Design Basis Documentation When Original Records Are Lost
OSHA addresses the common situation where original relief system design basis documents no longer exist. OSHA expects the employer to reconstruct the design basis through engineering analysis, not to operate without it.
Read OSHA Letter ↗
Feb 4, 2013
Relief System Changes and MOC Requirements
OSHA confirms that changes to relief valve setpoints, replacement with different capacity devices, or modifications to the discharge header system require MOC. The relief system is a safety-critical system whose design basis must be maintained current.
Read OSHA Letter ↗
Dec 22, 2003
PSI Package Completeness and Relief System as Required Element
OSHA clarifies that the PSI package is incomplete without relief and vent system documentation. An incomplete PSI package is a direct violation and is not cured by the fact that the systems themselves are functional.
Read OSHA Letter ↗
⚡ Key Compliance Takeaway
If you cannot find the original relief system design basis, reconstruct it through engineering analysis before your next PHA or MI inspection. Operating a covered process without documented relief system design basis is a PSI violation, not a future-improvement item.