TABLE OF CONTENTS Ideally, would you rather perform a HAZard and OPerability study (HAZOP) on a plant before you build it, or afterwards? The obvious answer is before, but not everyone who is asked this question realizes the real reason why. It's cheaper to redesign the plant on paper. The alternative would be to rebuild the plant after the fact. The same applies to safety systems.
As described above in Section 8.1, things are not as intuitively obvious as one may wish. Deciding which system is appropriate for a given application is not always a simple matter. It's therefore important to be able to analyze systems in a quantitative manner. While quantitative analyses may be imprecise (as will be stressed shortly), they are nevertheless a valuable exercise for the following reasons:
They provide an early indication of a system's potential to meet the design requirements.
They enable lifecycle cost comparisons.
They enable one to determine the weak link in the system (and fix it, if necessary).
They allow an "apples to apples" comparison between different offerings.
"There are lies, there are damn lies, and then there's statistics."
M. Twain
Simple models may be calculated and solved by hand. As more factors are accounted for, however, manual methods become rather unwieldy. It's possible to develop spreadsheets or other computer programs to automate the process. A major drawback of some models is often not what they include,...
