Towards Bespoke 3D Fire & Gas Mapping: Integration of Risk-Based Approach and CFD Modelling

Fire and Gas Detection Systems (FGDS) are critical tools in a plant utilised to minimise risk to personnel, the environment and the facility. Well-configured systems will facilitate the isolation of leaking inventories and expedite timely escape and evacuation of personnel. Typically, the systems are used to detect leaks and dangerous build-up of toxic or flammable gas or the presence of fires that may cause escalation. Systems should be configured to minimise potential spurious alarms which interrupt production output at a minimum cost.

Historically, a prescriptive-based approach has been applied during the placement of these detectors, which in itself is typically based on engineering judgement. Modern Fire and Gas Mapping tools are becoming more widespread in order to understand the optimum number and layout of the detectors in question.

As outlined in International Society of Automation (ISA) technical report (TR 84.00.07), two approaches can be utilised by the modern Fire and Gas Detection Mapping tools. A more traditional ‘geographic approach’ can be utilised to estimate detector coverage and determine their numbers in a three-dimensional (3D) environment. However, this paper discusses the more sophisticated ‘3D risk-based approach’ which can be employed to combine consequence and frequency analyses with the aim to compare the results against company risk criteria. For risk-based Fire and Gas Detection Mapping, the As Low As Reasonably Practicable (ALARP) concept is used to judge the acceptability of detector configurations. Concepts from Fire and Gas Detection Mapping, Quantitative Risk Assessment (QRA), Reliability and SIL (IEC 61511) are incorporated to ensure an in-depth analysis, consistent with site asset integrity and safety studies.

Furthermore, advanced Computational Fluid Dynamics (CFD) modelling can be integrated into the mapping process: by performing detailed consequence analysis, the calibration of the performance targets can be achieved by potential optimization of the target gas cloud size based on more accurate explosion hazards. This ensures a more realistic design, specific to the facility of interest.

This paper aims to highlight that, through the implementation of a ‘3D risk based approach’ and the integration of detailed CFD modelling for the placement and coverage of detectors, the magnitude of the consequence, frequency of occurrence and the relative risk reduction effectiveness can be investigated and utilised in ensuring the risk is ALARP. This presentation utilises a sample study on an existing facility to demonstrate the application of a risk-based approach along with its general findings.