Chapter 15: SIS Design Checklist

Introduction

The use of a checklist will not, in and of itself, lead to safer systems, just as performing a HAZard and OPerability study (HAZOP) and not following any of the recommendation will not lead to a safer facility. Following the procedures outlined in the checklist, which are based on industry standards and accumulated knowledge (much of which was learned "the hard way"), should result in safer systems. The checklist is an attempt to list as many procedures and common practices as possible in the hope that, by following a systematic review of the overall design process, nothing will fall through the cracks of an organization and be forgotten.

This checklist is composed of various sections, each corresponding to different portions of the safety lifecycle as described in various standards. Different sections of the checklist are intended for different groups involved with the overall system design, ranging from the user, contractor, vendor, and system integrator. Exactly who has what responsibility may vary from project to project. The checklist, therefore, does not dictate who has what responsibilities, it only summarizes items in the various lifecycle steps.

Why bother? The English Health and Safety Executive reviewed and published the findings of 34 accidents that were the direct result of control and safety system failures. Their findings are summarized in Figure 15-1. Forty-four percent of the accidents were due to incorrect and incomplete specifications (functional and integrity), and 20% due to changes made after commissioning. One can easily see that the majority...