What-If Analysis is a structured brainstorming technique used to identify hazards, operability problems, and potential accident scenarios by systematically asking “what if” questions about a process, system, or procedure.
In the context of IEC 61511 and process hazard analysis (PHA), What-If Analysis is one of several accepted methods for identifying hazardous scenarios during the design or modification of a safety-instrumented system. The results — a list of credible scenarios, consequences, and existing safeguards — feed directly into risk assessment activities such as layer of protection analysis (LOPA) to determine whether additional risk reduction is required.
What-If Analysis is less structured than a HAZOP study but faster to execute and well-suited to simpler systems or early design stages. It can be enhanced by pairing it with a checklist, commonly called a What-If/Checklist analysis, to improve coverage. The depth and quality of the results depend heavily on the experience and diversity of the review team.
Key Points:
- A qualitative hazard identification technique — not a quantitative risk calculation
- Structured as a series of “what if” questions, typically organized by process section, equipment, or operating mode
- Output includes hazard scenarios, potential consequences, existing safeguards, and recommended actions
- Accepted by IEC 61511 and CCPS as a valid PHA method for identifying initiating events and consequences
- Less resource-intensive than HAZOP but may miss more subtle or systemic hazards
- Results feed into risk assessment methods such as LOPA to determine whether a safety instrumented function (SIF) and target SIL are required
Example:
During a design review of a chemical reactor feed system, a What-If Analysis team asks: “What if the feed valve fails open?” The consequence is reactor overpressure, potentially causing a rupture and toxic release. The existing safeguard is a pressure relief valve. If the residual risk after crediting the relief valve still exceeds the tolerable risk target, a safety instrumented function (SIF) may be required to achieve the necessary risk reduction factor (RRF) and meet the target SIL.
See Also: LOPA, HAZOP, tolerable risk, target SIL, bowtie analysis, FTA, ETA
Cited Source:
- IEC 61511-1:2016, Clause 8
- CCPS — Guidelines for Hazard Evaluation Procedures
- ISA — IEC 61511 Functional Safety Standard