TABLE OF CONTENTS "Everything should be made as simple as possible, but no simpler."
Albert Einstein
Chapter 7 dealt with the pros and cons associated with various logic system technologies. Designing an SIS, however, involves much more than just choosing a logic box. Chapter 9 dealt with field device issues. This chapter will deal with other management, hardware, and software considerations. Some aspects of system design are impossible to quantify in a reliability model (the topic of Chapter 8), yet they can have a profound impact on system performance.
The goal of many engineers and companies is to develop a "cookbook" for system design. The senior engineers, with their experience and knowledge, will write down rules and methods to be followed by the junior engineers. One must be cautious, however; one set of rules or procedures simply can't apply to all systems and organizations.
Section 5 of IEC 61511 covers the management of functional safety. The standard naturally focuses on issues related to safety instrumented systems, not general health and safety issues. IEC 61511 states that policies and strategies for achieving safety need to be identified, along with a means of evaluating its achievement. People and departments need to be identified and informed of their responsibilities. Personnel need to be competent to carry out their assigned activities. Competency is a function of knowledge, experience, and training. Competency requirements need to be defined and documented.
Many system problems are due to two simple...
