What-If analysis worksheet

Table 4.7. Typical Format for a What-if Analysis Worksheet...

DOCUMENTING THE RESULTS. The what-if analysis produces a tabular listing of narrative-style questions and answers that constitute potential accident scenarios their qualitative consequences and possible risk-reduction methods. Table 4.7 shows the format of a what-if analysis worksheet. Although some what-if analyses are documented in a narrative-style format, a table makes the documentation more organized and easier to use. 

Figure 14.2 shows the partially complete what-if analysis worksheet for the vapor degreaser facility. Note that many more what if questions can (and should be) asked to completely exhaust all possible events that could affect the safety of overall system operation. Quite typically, a properly completed what-if analysis will address many dozens of individual items and encompass numerous worksheet pages before all credible events have been evaluated. The intent of Figure 14.2 is to... 

WHAT-IF ANALYSIS WORKSHEET AREA Vapor Decreaser TEAM MEMBERS J. Doe T. Smith C. Hope V. Jones A. Ford DATE 16 November 2004 PAGE 1 of 1 ... 

Figure 14.2 Partially completed what-if analysis worksheet for the vapor degreaser system.

The questions should continue until all elements are addressed. If a more detailed and complete HAZOP study should be required, the information contained on the what-if analysis worksheets will help facilitate and streamline the pending HAZOP study. 

Taking the above stated differences between the What-If Analysis Worksheet and the HAZOP process. Figure 14.3 provides an example of a typical HAZOP Worksheet. Note the headings over each column. Some are identical to those found on the What-If worksheet and, therefore, transfer of the information from any previous What-If... 

ACRONYMS AND ABBREVIATIONS WHAT-IF ANALYSIS WORKSHEETS HAZOP REVIEW WORKSHEETS... 

A typical what-if analysis worksheet is shown in Figure 2.93. 

As with numerous other analytical techniques presented and discussed in this text, a worksheet developed for the what-if analysis greatly facilitates the documentation and review of data points. Figure 14.1 provides an example of a what-if worksheet. By placing specific questions in the what if..column, the analyst can evaluate the consequences of credible hypothetical situations and events. 

In the worksheet Example 12-5, invoke GOALSEEK nsing Data I What-If Analysis Goal Seek. In the GOALSEEK dialog box, enter the data as shown in Eignre 12-3 and click the OK button. In this case, cell D3 is changed until the value of the formula in cell A6 equals 250. 

A worksheet (data base spreadsheet) form is used to collect and collate the process hazard analysis review data. A computer software generated spreadsheet is typically used. For a complete description of commercially available HAZOP or What-If software, the user should refer to the manufacturer s HAZOP or What- If software User Instructions. Although pre-printed forms may be used, they are highly inefficient and should be maintained only as a backup in case of computer hardware or software failures. 

Table 3.3 Example of what-if worksheet for preliminary hazard analysis. 

The analysis team starts with a full set of process and instrument diagrams (P IDs). The team considers possible abnormal events or combinations of events and reviews planned safeguards (e.g. interlocks, relief valves) for adequacy. The final report includes all "what-if" worksheets, a prioritized listing of identified hazards, and the modifications recommended to reduce the hazards to an acceptable level. 

In system safety, inductive analysis tends to be for hazard identification (when the specific root causes are not known or proven), and deductive analysis for root cause identification (when the hazard is known). Obviously, there is a fine line between these definitions because sometimes the root causes are known from the start of an inductive HA. This is why some analysis techniques can actually move in both directions. The PH A is a good example of this. Using the standard PHA worksheet, hazards are identified inductively by asking what if this component fails, and hazards are also identified by deductively asking how can this UE happen. 

Keep the worksheets in the database updated. If you can do that, then the next time you do a safety analysis, use the database as a baseline document and just change what needs to be modified. Be careful not to assume that two systems are exactly alike. We all know that they are not. 

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