Hazard Studies & Risk Assessment

Fire & Gas Mapping (F&G Mapping)

ISA TR84.00.07 performance-based detector coverage — built on 3D geometry and dispersion physics

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What this study delivers

Fire & Gas
Mapping (F&G Mapping)

Performance-based F&G design, codified by ISA TR84.00.07 (2018) and increasingly demanded by IEC 61511 SIL claims, replaces the historical prescriptive grid (one detector per 15 m × 15 m, etc.) with quantitative coverage analysis. The methodology combines 3D plant geometry, target gas cloud size (defined per facility risk criteria — typically 5 m, 10 m, or scenario-specific), detector field-of-view modelling (cone angles, line-of-sight obstruction for flame detectors, open-path geometric coverage), and voting logic (1ooN, MooN) optimisation. Geographic coverage answers 'what fraction of plant volume is detected'; scenario coverage answers 'what fraction of credible release scenarios trigger voted alarm within target time'. The discipline became unavoidable after several incidents (Texas City 2005, Caribbean Petroleum 2009) where gas releases reached escalation despite nominally-compliant detector counts.

Fire & Gas Mapping (F&G Mapping) — Overview
Study execution

How the study is executed

A structured, facilitated process — from scope definition through close-out — producing defensible, actionable outputs.

Performance Target & Cloud Size Definition

Establish facility-specific performance targets per ISA TR84.00.07 (typically ≥90% geographic and scenario coverage); define target gas cloud size (commonly 5 m or 10 m³ LFL cloud) from VCE consequence modelling; specify flame target size (0.1–1.0 m² at LFL).

3D Plant Geometry Import & Release Scenarios

Import plant geometry from CAD, point cloud, or PDMS / E3D model; overlay equipment and structure footprints; define release inventory and source locations per FERA / QRA scenario list; model representative dispersion cases (weather-binned, stability-class weighted) for scenario coverage analysis.

Gas Detector Siting — Point & Open Path

Optimise point gas detector locations against dispersion contour density and wind-rose weighting; site open-path detectors for beam coverage with obstruction avoidance and false-alarm management per path-blockage probability; assess catalytic vs electrochemical vs IR technologies per service environment.

Flame Detector Field-of-View Modelling

Model UV/IR, multi-spectrum IR, and video-based flame detector cone angles with line-of-sight obstruction analysis across 3D geometry; optimise detector orientations to achieve target fire-size detection; identify coverage shadow zones requiring supplementary detectors or active protection upgrade.

Coverage Performance Analysis & Gap Closure

Calculate geographic coverage (fraction of plant volume detected) and scenario coverage (fraction of credible releases triggering voted alarm within target time) per ISA TR84.00.07; identify coverage gaps; iterate detector placement to meet target; document sensitivity to detection threshold and voting scheme.

Voting Logic, SIL Claim & Specification Package

Specify voting logic (1ooN vs MooN) balancing response speed against spurious-trip rate; allocate SIL for F&G SIFs per IEC 61511 with PFD / PFH calculation; issue detector schedule, cause-and-effect input, procurement specifications (FM / SIL-certified), and IEC 62443 cybersecurity overlay.

Fire & Gas Mapping (F&G Mapping) — Scope
Study scope

What the study covers in full

Target gas cloud and fire size definition per facility risk tolerance (typically a 5 m or 10 m equivalent cloud dimension)
Geographic coverage analysis — 3D plant geometry import (CAD, point cloud, PDMS / E3D)
Scenario coverage analysis — release modelling with weather and stability binning
Flame detector field-of-view modelling with line-of-sight obstruction (UV/IR, multi-spectrum, video)
Point gas detector siting per dispersion contour and ventilation flow
Open-path gas detector geometric coverage with beam-block and false-alarm management
Voting logic optimisation — 1ooN for fastest response, MooN to suppress nuisance trips
Performance target setting (typically ≥90% coverage at voted threshold per ISA TR84.00.07)
SIL allocation for F&G SIFs per IEC 61511 with PFD / PFH calculation
Cybersecurity-aware detector network design per IEC 62443
Why it matters

Outcomes of Fire & Gas Mapping (F&G Mapping)

Detection Coverage Assurance
  • Surfaces the silent coverage gaps that prescriptive grids hide — typically 20–40% of credible scenarios
  • Drives flame-detector siting that actually sees through structural obstruction
  • Captures voting logic that survives single-detector failure or proof-test bypass
  • Defends realistic detection times for ESD activation
ISA TR84.00.07 / IEC 61511 Defence
  • Audit-defensible under ISA TR84.00.07 performance-based justification
  • Provides SIL-claim evidence for F&G SIFs per IEC 61511
  • Withstands IEC 60079-29 and API RP 14C examination
  • Supports FM Global, AHJ, and underwriter scrutiny on credible detection
Voting Logic & Trip-Rate Management
  • Reduces nuisance trip frequency through engineered voting logic
  • Eliminates the redundant detectors that prescriptive grids accumulate
  • Drives proof-test scope and frequency to genuinely effective devices
  • Supports MOC for plant modification affecting coverage
Detector Count & Proof-Test Efficiency
  • Typically 15–30% reduction in detector count vs prescriptive grids — without coverage loss
  • Defers detector replacement capex by surfacing genuinely failed devices
  • Reduces proof-test labour through right-sized detector population
  • Tightens insurance pricing through demonstrated F&G design rigour
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