HAZOP = you imagine what could go wrong on paper. PSSR = you go to the field and confirm everything is actually ready before you press START.

 That infographic is one of the clearest summaries of two critical Process Safety barriers. Same goal - safer operations - but they happen at opposite ends of a project.

Think of it like this:

HAZOP = you imagine what could go wrong on paper. PSSR = you go to the field and confirm everything is actually ready before you press START.

HAZOP - Hazard and Operability Study

What it is: A structured, systematic brainstorming technique to find hazards before they happen.

Main purpose: Identify potential hazards, assess the risk, and find operability issues.

When is it done: During design, and whenever there is a major change. That includes process modification, new technology, new product, or after an incident. It is early in the lifecycle.

Focus: Process hazards and deviations from design intent. Examples: loss of containment, overpressure, high temperature, reverse flow, underperformance.

Who is involved: Multidisciplinary. Process, operations, maintenance, HSE, engineering, instrumentation, etc. You need different eyes in the room.

Method: You break the plant into nodes (e.g., a line from pump to reactor) and apply guidewords to parameters.

Guidewords like: No, More, Less, Reverse, As well as, Part of, Other than, High, Low.

Example: Parameter = Flow, Guideword = No -> "No Flow" -> What causes it? What is consequence? How do we prevent it?

Output: A HAZOP worksheet - list of deviations, causes, consequences, safeguards, and recommendations for risk reduction.

Frequency: Initially at design, then periodically and after every Management of Change.

PSSR - Pre-Startup Safety Review

What it is: A verification process. The final gate before you introduce energy or hazardous material.

Main purpose: Verify that all safety-critical systems are in place and correctly implemented for a safe start-up. This is a regulatory requirement under OSHA PSM 1910.119 and best practice everywhere.

When is it done: After construction, installation, and pre-commissioning are complete, but before the first introduction of hazardous material or energy. Also required after extended shutdowns or major modifications.

Focus: Readiness. Not theory, but reality: Is the equipment installed as per design? Are procedures written? Is documentation complete? Is training done? Are relief valves, interlocks, ESD tested?

Who is involved: Operations, maintenance, engineering, HSE, contractors, and sometimes regulators or owner's reps.

Method: Checklist-based. Review of documentation, site walkdowns, field inspections, punch list verification, loop checks, and confirmation against legal and company standards.

Output: A go/no-go decision. Either Approval to start-up, or a list of outstanding items that must be closed.

Frequency: Once, right before each start-up.

The KEY DIFFERENCE at the bottom

HAZOP = Look for what could go wrong (during design and changes).

PSSR = Confirm that what is in place is correct and ready (before start-up).

One identifies risks, the other ensures readiness. In the process safety lifecycle, HAZOP creates the recommendations (add an alarm, add a check valve, change the material). PSSR confirms those recommendations were actually implemented in the field.

Together they prevent incidents.

In an oil and gas or chemical plant scenario:

HAZOP in design says: "If cooling water fails, reactor will overpressure."

Recommendation: install high temperature interlock.

Months later during construction, PSSR checks: Is that interlock installed? Is it tested? Does operations know the procedure? If yes, you can start up. 🚧🏗️⛑️🚨🚥⚠️🗼🌡️🚦🦺

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