(131b) Designing an Effective Detection and Mitigation System for a Plant – Build on Facility Siting Study and QRA Investments

Designing an effective detection and mitigation system for a plant – build on Facility Siting Study and QRA investments.

Many plants worldwide are moving forward from conducting only consequence-based analyses to risk based siting analyses. Additionally, operators are relying more on instrumented systems to reduce outdoor personnel tasks, and to allow them to work further from process units. As these developments occur, plant operators are looking for ways to account for these changes when quantitatively determining the amount of risk reduction. One such approach on reducing risk is installation of a fire and gas detection system that can be used in conjunction with isolation to mitigate a hazard before it develops into a major gas release, explosion, or fire. By utilizing this approach, risk reduction credit can be taken for high consequence loss of containment scenarios which can dominate consequence based evaluations. However, the implementation of these systems is typically performed in an empirical manner. With the qualitative approach, sites are not able to implement such systems in a consistent manner and, as a result, they are not able to take credit for such systems in the calculations of their overall risk values.

Some of the questions being asked are: how many detectors are needed? Where to install them? Will the detection be effective? Most importantly, if the dispersion or fire is detected, can it be mitigated? All of these questions can be answered in a definitive manner using ISA’s S84 Technical Report 7 on Fire & Gas systems. ISA84 TR7 provides guidance on designing fire and gas detection and mitigation system using a performance-based standard.

In order to determine the effectiveness of gas detection system, a series of controlled dispersions tests were performed to validate the various approaches in industry. This paper combines the results from those tests along with numerous fire and gas mitigation studies performed to test the different aspects of a detection and mitigation system’s effectiveness. The paper proposes to discuss the numeric concepts of ISA84 TR7 pertinent to designing a fire and gas detection and mitigation system, and its impact to overall risk values for risk based siting studies. Methods of optimizing the number and types of detectors is also discussed.