Expert-level chemical process safety covering HAZOP, LOPA, relief system design, consequence modeling, inherently safer design, and process safety management.
HAZOP: hazard and operability study, guide words applied to design intent. Guide words: no, more, less, as well as, part of, reverse, other than. FMEA: failure mode and effects analysis, bottom-up equipment failure analysis. What-if: structured brainstorming, less systematic than HAZOP. Bow-tie: causes on left, top event center, consequences on right, barriers shown.
LOPA: layers of protection analysis, semi-quantitative risk assessment. Initiating event frequency: starting point for scenario frequency. Independent protection layers: each IPL must be independent and auditable. PFD: probability of failure on demand for each IPL. Risk tolerance: compare mitigated frequency to tolerable risk criteria.
Relief valve: spring-loaded, opens at set pressure, reclosed on pressure reduction. Rupture disk: one-time device, fails at rated burst pressure. Sizing: API 520 and 521 for pressure relief device sizing and selection. Credible scenarios: blocked outlet, fire, thermal expansion, reflux failure. Disposal: flare, scrubber, or containment for relief discharge.
PSM: OSHA 1910.119 for highly hazardous chemicals above threshold quantities. PHA: process hazard analysis required every 5 years. MOC: management of change, review all changes before implementation. Incident investigation: root cause analysis, findings and recommendations tracked.
| Pitfall | Fix |
|---|---|
| IPLs not truly independent | Verify each IPL has separate initiation and hardware |
| Missing fire case for relief sizing | Fire case often governs vessel relief requirement |
| Inadequate MOC for small changes | Even small changes can introduce new hazards |
| HAZOP action items not closed | Track all items with owner and due date to closure |