AutoQuiz is edited by Joel Don, ISA's social media community manager.

This automation industry quiz question comes from the ISA Certified Automation Professional (CAP) certification program. ISA CAP certification provides a non-biased, third-party, objective assessment and confirmation of an automation professional's skills. The CAP exam is focused on direction, definition, design, development/application, deployment, documentation, and support of systems, software, and equipment used in control systems, manufacturing information systems, systems integration, and operational consulting. Click this link for more information about the CAP program.

Common terms used to quantify dangerous failures include which of the following?

a) probability of failure on demand (PFD) and nuisance trip rates
b) probability of failure on demand (PFD), risk reduction factor (RRF), and safety availability (SA)
c) mean time between failure, spurious (MTBFsp); nuisance trip rates; and safety availability (SA)
d) mean time between failure, spurious (MTBFsp) and risk reduction factor (RRF)
e) none of the above

Click Here to Reveal the Answer

PFD, RRF, and SA are extremely important in quantifying dangerous failures.

  • Probability of failure on demand: A value that indicates the probability of a system failing to respond to demand when a failure occurs.
  • Risk reduction factor: RRF = 1/PFD
  • Safety availability: SA = 1 – PFD

The correct answer is B, probability of failure on demand (PFD), risk reduction factor (RRF), and safety availability (SA). Spurious trips and nuisance trips are indicative of “safe” failure modes, not “dangerous” failures. This makes answers A, C, and D incorrect.

Reference: ANSI/ISA-84.00.01-2004 standard

About the Editor
Joel Don is the community manager for ISA and is an independent content marketing, social media and public relations consultant. Prior to his work in marketing and PR, Joel served as an editor for regional newspapers and national magazines throughout the U.S. He earned a master's degree from the Medill School at Northwestern University with a focus on science, engineering and biomedical marketing communications, and a bachelor of science degree from UC San Diego.

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