TABLE OF CONTENTS Barriers are those systems and actions that prevent escalation from occurring. The importance of barriers is well illustrated by comparison of the outcome from two actual events each involving a medium sized gas leak in the compression area of a platform. The worst case, the Piper Alpha disaster on 6.7.1988 is well known, the explosion on the Brent Alpha platform on 5.7.1988 is less well known. This accident started in exactly the same way as the Piper Alpha accident. The result was a gas fire following the explosion, brought under control in some 45 minutes due to automatic systems, with only superficial damage to the compression module. The dramatic difference between the two events arose because on the Brent Alpha platform, the barriers functioned as intended, while on Piper Alpha they did not. Some more details about these two accidents are presented in Subsection 8.1.1.
This section discusses the modelling of barriers in the event tree, with respect to their functionality, reliability and availability as well as the survivability of the systems, sometimes called, vulnerability to accidental loads.
Analysis of the functionality of the barriers involves determining whether they are capable of performing their intended function. As an example, gas detectors of the catalyst type have often been 'poisoned' by salt and other contaminations. Fire water systems may be clogged with dirt, rust and other particles, to an extent that the required fire water capacity can no longer be provided.
The analysis of functionality is...
