Risk Assessment: Theory, Methods, and Applications

CHAPTER 12

BARRIERS AND BARRIER ANALYSIS

12.1 INTRODUCTION

Most well-designed systems have protection equipment or other features to protect people, the environment, and other assets against harm should failures or dangerous deviations occur in the system. The equipment and features that are installed for this purpose are called safety barriers, or simply barriers. Several other names are used in the literature, for example: countermeasures, safety functions/systems, safety critical functions/systems, defense measures, defenses, lines of defense, layers of protection (or protection layers), and safeguards. In this book, we use mainly the term barrier, but other terms will also be used in relation to methods that center on an alternative term: for example, the layer of protection analysis (LOPA) method.

Barriers have been mentioned in several previous chapters without a proper definition. The aim of this chapter is to define and discuss the barrier concept and to show how barriers can be classified into special categories. A special type of barrier, called safety instrumented systems, is described in more detail, and some methods for barrier analysis are introduced. These methods are:

• Hazard-Barrier Matrices enter into a simple qualitative method that identifies all hazards in a system and all the barriers that have already been, or are planned to be, introduced to protect against these hazards. The hazards and the barriers are displayed in a matrix diagram that can be used to ...