March 2010

ISA Certified Automation Professional (CAP) program

Certified Automation Professionals (CAPs) are responsible for the direction, design, and deployment of systems and equipment for manufacturing and control systems.

CAP question

In Safety Instrumented System design and Safety Integrity Level Selection, what is the most common top-down approach for describing the failures of complex systems?

A. Fault Tree Analysis

B. HAZOP Analysis

C. Root-Cause Analysis

D. Markov Analysis

CAP answer

The correct answer is A, Fault Tree Analysis.


A fault tree analysis begins with the "top event," which is the result of a number of basic events that contribute to, or initiate, the system failure.  The logic of a fault tree is displayed by the symbols that represent the basic events and gates that logically relate those events.

References: Edward M. Marszal, P.E., C.F.S.E and Dr. Eric W. Scharpf, MIPENZ; Safety Integrity Level Selection - Systematic Methods Including Layer of Protection Analysis, ISA Press, 2002.