Introduction to functional safety assessments of safety controls, alarms, and interlocks: How efficient are your functional safety projects?


  • This article was originally presented at the ISA Houston Section monthly luncheon, Houston, Texas, October 5, 2016, followed by a poster at the 2016 International Symposium, College Station, Texas, October 25–27, 2016.


The return on investment (ROI) for safety controls, alarms, and interlocks (SCAI) can be significantly impacted by human error, which can occur during any lifecycle activity and be committed by competent workers. Design, installation, testing, maintenance, and operational practices are often repeated throughout a site, lowering the ROI with each flawed installation. A functional safety assessment (FSA) is a tool used to identify and correct defects before a simple human error allows an incident to propagate in spite of the capital spent on the installed SCAI equipment.

Significant efficiency can be gained when FSAs are periodically conducted during the SCAI lifecycle, so that critical information is gathered when needed. This article will discuss the internationally endorsed five-stage approach to FSA. The purpose and content of each FSA stage is reviewed and execution timing is suggested that focuses project resources to maximize FSA benefit to project cost and schedule. Finally, a case study illustrates how lack of effective and timely FSA contributed to the occurrence of a costly and catastrophic loss event. © 2017 American Institute of Chemical Engineers Process Saf Prog 36: 392–398, 2017