Limitations of the What-If Analysis

DOE-HDBK-1100-2004

4.2.4 Limitations of the What-If Analysis

The what-if analysis is a powerful PrHA method if the analysis team is experienced and well

organized. Otherwise, because it is a relatively unstructured approach, the results are likely to

be incomplete.

4.2.5 Example What-If Analyses

Partial what-if analyses for the two example processes described in Section 4.0 are shown in

Tables 4.9 and 4.10. Although for actual, more complex analyses, the what-if tables for each

line or vessel would be separate, for these examples, a single table was developed. A

preliminary hazard analysis (PHA) would identify that the intrinsic hazards associated with HF

are its reactivity (including reactivity with water, by solution), corrosivity (including carbon

steel, if wet), toxicity via inhalation and skin contact, and environmental toxicity. The N2

supply system pressure is not considered in this example. The specific effects of loss of

containment could be explicitly stated in the "loss of HF containment" scenarios identified.

Similarly, the effects of loss of chlorine containment, including the reactivity and toxicity of

chlorine, could be specified for the second example.

4.3

What-If/Checklist Analysis

The purpose of a what-if/checklist analysis is to identify hazards, consider the types of accidents

that can occur in a process or activity, evaluate in a qualitative manner the consequences of

these accidents, and determine whether the safety levels against these potential accident

scenarios appear adequate. The what-if/checklist analysis is described in detail in Guidelines for

Hazard Evaluation Procedures (CCPS, 1992).

4.3.1 Description of the Method

The what-if/checklist analysis method combines the creative, brainstorming features of the

what-if analysis with the systematic features of the checklist analysis. The PrHA team uses the

what-if analysis method to brainstorm the types of accidents that can occur within a process.

Then the team uses one or more checklists to help fill in any gaps. Finally, the team members

suggest ways for reducing the risk of operating the process. The what-if analysis encourages the

PrHA team to consider potential accident events and consequences that are beyond the

experience of the authors of a good checklist and, thus, are not covered on the checklist.

Conversely, the checklist lends a systematic nature to the what-if analysis.

Normally, a what-if/checklist analysis is used to examine the potential consequences of accident

scenarios at a more general level than some of the more detailed PrHA methods. It can be used

for any type of process at virtually any stage in its life cycle. However, this method is generally

used to analyze the more common hazards that exist in a process.

4.3.2 Analysis Procedure