Service
Process Hazard Analysis (PHA)
Systematic, well-facilitated hazard studies that find credible scenarios, test the safeguards against them and produce recommendations people can act on.
What a process hazard analysis is
A process hazard analysis (PHA) is a structured, team-based review that asks a deceptively simple question: what can go wrong in this process, how bad could it be, and is what we have in place enough to prevent or mitigate it?
A good PHA works systematically through the process — line by line, step by step, or equipment item by equipment item — to identify deviations from design intent, trace them back to credible causes and forward to their consequences, and evaluate the safeguards between the two. Where safeguards appear inadequate, the team makes recommendations.
The PHA is the foundation of the rest of a process safety program. Its scenarios feed LOPA and SIL targeting, relief system design, operating procedures, training, emergency planning and mechanical integrity priorities. When the PHA is weak, every downstream activity inherits the weakness.
Why it matters
Many of the most consequential industrial accidents involved scenarios that had either never been analyzed or had been analyzed and accepted with safeguards that did not perform as assumed. Common PHA weaknesses we see include:
- Nodes drawn too large, so specific deviations are glossed over.
- Safeguards credited that are not independent of the initiating cause — for example, an alarm on the same transmitter that failed.
- Non-routine modes — startup, shutdown, maintenance, upsets — treated as an afterthought.
- Revalidations that copy the previous study without testing it against changes, incidents and current knowledge.
- Recommendations worded so vaguely that no one can tell when they are complete.
- Facility siting and human factors addressed with a generic checklist rather than real discussion.
Methodologies we use
The right technique depends on process complexity, the stage of the project and the hazards involved. Frequently a study combines more than one method.
| Method | How it works | Best suited to |
|---|---|---|
| HAZID | Broad, guideword- or checklist-prompted identification of major hazards early in a project. | Concept and front-end design; site selection; new technologies. |
| HAZOP | Applies guidewords (No, More, Less, Reverse…) to process parameters at each node to generate deviations. | Complex continuous processes with detailed P&IDs; new designs and revalidations. |
| What-If | Team brainstorms "what if…" questions about equipment, operations and external events. | Simpler processes; procedures; changes; experienced teams. |
| What-If / Checklist | Combines What-If creativity with structured checklists to ensure coverage. | Well-understood processes such as ammonia refrigeration, storage and transfer. |
| Checklist | Compares the design and operation against an established list of requirements and good practices. | Standard equipment; code-driven reviews; supplementing other methods. |
| FMEA | Examines each component's failure modes and their effects on the system. | Mechanical and electrical systems, packaged equipment, instrumented systems. |
| Procedural HAZOP | Applies guidewords to steps in an operating procedure (omitted, too early, wrong order…). | Batch operations, startups, shutdowns, transfers and maintenance tasks. |
OSHA's PSM standard lists What-If, Checklist, What-If/Checklist, HAZOP, FMEA and Fault Tree Analysis, or an appropriate equivalent, as acceptable methodologies for covered processes.
HAZOP deviation explorer
HAZOP generates deviations by combining a guideword with a process parameter. Choose a parameter and a guideword below to see the resulting deviation with illustrative causes, consequences and safeguards. The examples are generic; real studies are always node-specific.
Guideword × parameter
Illustrative examples for a typical liquid transfer node
Select a parameter and a guideword.
How we run a PHA
- Scope and plan
Define boundaries, nodes, the methodology, risk criteria and the team. Confirm the study supports regulatory and corporate requirements.
- Verify process safety information
Review P&IDs, material data, design bases, relief and SIS documentation and incident history. Gaps are logged before the sessions, not discovered during them.
- Facilitate the sessions
An experienced facilitator and a dedicated scribe lead a multidisciplinary team — operations, engineering, maintenance and, where relevant, instrumentation and EHS — on site or remotely.
- Address cross-cutting topics
Previous incidents, facility siting, human factors, non-routine modes, and the consequences of control failures are addressed explicitly.
- Rank and recommend
Scenarios are risk-ranked against your criteria; high-consequence scenarios are flagged for LOPA. Recommendations state the hazard, the intent and a verifiable completion basis.
- Report and close
A defensible report is issued for review, and we can support recommendation resolution and tracking to closure.
Regulatory and standards basis
- OSHA 29 CFR 1910.119(e) requires an initial PHA for PSM-covered processes, performed by a team with process expertise and at least one person knowledgeable in the methodology, updated and revalidated at least every five years, with recommendations promptly resolved and documented.
- EPA 40 CFR Part 68 requires a PHA for Program 3 processes and a hazard review for Program 2 processes.
- IEC 61511 / ISA 61511 requires a hazard and risk assessment as the starting point of the safety instrumented system lifecycle.
- CCPS guidance, including Guidelines for Hazard Evaluation Procedures, is widely recognized as good practice for method selection and execution.
Typical deliverables
- Study plan: scope, node list, methodology, team roster and risk matrix
- PSI gap list issued before sessions
- Complete worksheets in your preferred format or software
- Risk-ranked recommendations with completion criteria
- Facility siting and human factors records
- Scenario list flagged for LOPA, SIL or relief review
- Final report suitable for regulatory inspection
- Optional: recommendation tracking and closure support
Frequently asked questions
How often must a PHA be revalidated?
For processes covered by OSHA PSM and EPA RMP Program 3, the PHA must be updated and revalidated at least every five years. Many companies also revalidate after major changes or significant incidents.
Can a PHA be conducted remotely?
Yes. Remote and hybrid sessions work well when process safety information is current and participants are prepared. Site walk-downs and in-person sessions remain valuable for complex units and first-time studies.
How long does a HAZOP take?
It depends on the number and complexity of nodes. As a rough planning figure, teams commonly cover a small number of nodes per session day. We estimate duration after reviewing the P&IDs and scope.
What is the difference between a revalidation and a redo?
A revalidation tests the existing PHA against changes, incidents and current knowledge and updates it. If the original study is deficient or the process has changed substantially, a full redo is more defensible.
Which PHA software do you use?
We can work in the software your company has standardized on, or provide worksheets in a portable format. Ask us about your preferred tool.
Planning a PHA or revalidation?
Send us the scope: number of units or nodes, methodology preferences and target dates. We will propose a team and schedule.