What-If Analysis (or what if checklist) 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. It is the “H” portion of an H&RA. The results are a list of credible scenarios, consequences, and existing safeguards. They 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.
How it fits: For an overview of how What-If analysis fits alongside the other hazard and risk analysis methods in an IEC 61511 H&RA, see Hazard and Risk Analysis Methods.
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