OSHA requires that PHAs be updated and revalidated at least every five years. But when does the five-year clock start? From the date the PHA team begins work, from the date the study is completed, or from when management accepts the findings? These letters clarify the triggering event and address related questions including whether a partial revalidation satisfies the requirement, what happens when a process undergoes major modification between cycles, and whether a new process's initial PHA resets the clock. Getting the revalidation schedule wrong by even a few months can produce a multi-element PSM violation.

What OSHA Has Said

Jan 22, 1998
Revalidation Clock and Completion Date vs. Initiation Date
OSHA clarifies that the five-year revalidation clock runs from the completion of the most recent PHA or revalidation, not from the start date of the study or the date management approves recommendations.
Read OSHA Letter ↗
Sep 20, 2019
Partial Revalidation and Phased Unit Updates
OSHA addresses whether a facility may conduct revalidation on a unit-by-unit basis over multiple years. OSHA confirms that each unit's five-year clock runs from its own completion date.
Read OSHA Letter ↗
Apr 16, 2020
Process Modification and Revalidation Clock Reset
OSHA evaluates whether a significant process modification resets the revalidation clock. A modification requiring MOC review and PHA update restarts the five-year clock for the affected portion of the process.
Read OSHA Letter ↗

⚡ Key Compliance Takeaway

Track revalidation completion dates, not start dates, and schedule your next cycle to finish before the five-year anniversary. A unit-by-unit approach is acceptable but each unit's clock runs independently. Major modifications that trigger MOC and PHA update reset the clock for those sections.