Under 29 CFR 1910.119(i)(1), a pre-startup safety review is required for new facilities and for modified facilities when the modification is significant enough to require a change in the process safety information. The review must confirm, before highly hazardous chemicals are introduced, that construction and equipment match design specifications, that safety, operating, maintenance, and emergency procedures are in place and adequate, that a PHA has been done and its recommendations resolved for new facilities (and MOC requirements met for modified ones), and that each operating employee has been trained. The letters below show how OSHA draws the line between a new facility, a modified facility, and a change that only needs MOC.

What OSHA Has Said

Jan 11, 1996
New facility vs. modified facility, and what each requires
Chevron asked where a modification ends and a new facility begins. OSHA explained that a facility built so it is physically separate and independent of existing facilities is a new facility, while one connected to or dependent on an existing facility is a modified facility. A PHA must be performed and its recommendations resolved before startup of a new facility. For modified facilities, the PSSR provision points to management of change rather than a new PHA. OSHA also said it "did not intend that a pre-start up safety review be conducted" for slight modifications that don't require a change in process safety information; those go through MOC unless they are replacement in kind.
Read OSHA Letter ↗
Sep 20, 2019
Restarting a process after an extended shutdown
The five-year PHA revalidation clock does not pause while a process is shut down. If it expires during the outage, the PHA must be revalidated before highly hazardous chemicals are reintroduced. OSHA listed what else an employer must do before restart, including MOC for changes since the last PHA, updated PSI and procedures, a review of training, a review of prior incident investigations and audits, and a pre-startup safety review before introducing HHCs into modified facilities under (i)(1) and (i)(2). The three-year refresher training requirement is also unaffected by the shutdown.
Read OSHA Letter ↗
Jan 5, 1995
A new facility and the timing of its first compliance audit
A new chemical plant that started up in June 1994 asked when its first compliance audit was due. OSHA confirmed that a PSSR is required for new facilities, and for modified facilities when the modification requires a change in PSI, and that the first three-year compliance audit could be completed by June 1997.
Read OSHA Letter ↗

⚡ Key Compliance Takeaway

The trigger is the process safety information. If a change is big enough that your P&IDs, design basis, or other PSI must be updated, plan a PSSR before any highly hazardous chemical goes back in. Smaller changes still need MOC unless they are true replacement in kind. Build the PSSR into turnaround and restart plans, and remember that a long shutdown does not stop the PHA revalidation clock.