Executive Summary
A specialty chemical manufacturer commissioning a newly constructed production unit — a continuous esterification process with associated solvent recovery and utility systems — required a Pre-Startup Safety Review (PSSR) prior to introducing hazardous materials and beginning operation. The unit had been engineered, procured, and constructed against an approved design basis that had itself been subject to HAZOP and SIL assessment during the design phase, but construction-phase deviations, vendor substitutions, and procedural readiness gaps are common at this stage and require independent verification before startup — which is precisely the function a rigorous PSSR serves. This representative example illustrates PSSR methodology and the categories of finding typical of new-facility startup review.
Facility Background
The unit comprised a continuous esterification reactor train, a distillation-based solvent recovery system, and associated utility tie-ins connecting to existing site infrastructure. The facility's design basis had been developed through a standard project sequence — process design, HAZOP, SIL determination and verification, detailed engineering, procurement, and construction — with the design-phase HAZOP and SIL work completed approximately 18 months before mechanical completion. Across that period, the project had experienced the changes typical of any capital project of this scale: several vendor equipment substitutions made for procurement or lead-time reasons, field-routing changes to piping and instrumentation made during construction to resolve clashes, and the normal accumulation of punch-list items addressing minor as-built deviations from design drawings.
Hazard Profile
- —Esterification reaction hazards consistent with the unit's design-phase HAZOP and SIL basis
- —Flammable solvent handling in the recovery system
- —High-temperature distillation operation
- —Risk that as-constructed and as-prepared facility conditions no longer match the basis against which these hazards were originally assessed and controlled
Study Methodology
- 1.Design-basis conformance review, comparing as-built P&IDs and equipment specifications against the design-basis documents subject to the original HAZOP and SIL assessment
- 2.Safety instrumented function verification, confirming each SIF specified during design-phase SIL assessment was actually installed, correctly configured, and functionally tested per its SRS
- 3.MOC closure verification, confirming every field change made during construction had been processed through the project's Management of Change procedure
- 4.Operating procedure readiness review, confirming procedures reflected the as-built configuration and that operating personnel had been trained against the current version
- 5.Punch-list safety relevance screening, distinguishing open items with potential safety relevance from purely cosmetic items
- 6.Mechanical integrity and pre-commissioning verification, confirming pressure testing, instrument calibration, and relief device certification were completed and documented
Key Findings
- —Two vendor equipment substitutions made during procurement had not been re-assessed against the original SIL basis, including a control valve with a different fail-safe action than assumed in the design-phase SIL verification calculation
- —Three field-routing changes to piping had been implemented without formal MOC processing, treated by the construction team as routine installation adjustments rather than process safety-relevant changes
- —Operating procedures for two startup sequences referenced the original design-basis piping configuration, which had since changed via the field-routing modifications
- —One relief device on the solvent recovery system had been installed but not yet certified, with documentation still in transit from the testing vendor
Risk Reduction Measures
- —The substituted control valve's fail-safe action corrected to match the SIL-verified design basis before startup, with the SIL verification calculation re-confirmed
- —The three field-routing changes formally processed through MOC retroactively, with hazard screening confirming no adverse safety impact and as-built documentation updated
- —Operating procedures for the two affected startup sequences revised to reflect the as-built piping configuration before operator training was finalized
- —Startup held pending receipt and verification of relief device certification documentation
Lessons Learned
Construction-phase changes accumulate through channels separate from a project's formal MOC process unless teams are explicitly trained to recognize their safety relevance.
Field teams resolving a piping clash or substituting an equivalent vendor component under procurement pressure do not always recognize these as process-safety-relevant changes requiring hazard re-screening — a PSSR's design-basis conformance review is specifically structured to catch exactly this category of drift before startup.
A SIL verification calculation is only valid for the specific equipment configuration it was calculated against.
A seemingly minor vendor substitution — a different fail-safe action on a control valve — can silently invalidate a SIL verification calculation's core assumption, detectable only by explicitly re-checking installed equipment specifications against the SRS.
PSSR findings are not a sign of poor project execution — they are the expected and intended output of a properly rigorous review.
A PSSR that finds nothing is more likely to indicate an insufficiently thorough review than a flawlessly executed project; the categories of finding in this example are the standard, expected findings of rigorous PSSR practice across new facility startups generally.
Technical Takeaways
- —Treat every vendor equipment substitution during procurement as a mandatory trigger for re-checking relevant SIL verification calculation assumptions
- —Train construction and field engineering teams to recognize piping and instrumentation routing changes as MOC-relevant, with a low threshold for escalation
- —Verify operating procedures against as-built configuration specifically, not against original design-basis documentation, as a standing PSSR checklist item
- —Confirm certification documentation is in hand — not merely in progress — before authorizing startup