Fire and Gas Mapping (F and G Mapping)
Performance based detector coverage to ISA TR84.00.07, built on 3D geometry and dispersion physics
Fire and Gas Mapping
(F and G Mapping)
Performance based fire and gas design, set out in ISA TR84.00.07 and increasingly demanded by IEC 61511 SIL claims, replaces the historical prescriptive grid of one detector every fifteen metres with quantitative coverage analysis. Our methodology combines your 3D plant geometry, a target gas cloud size defined by your facility risk criteria and usually set at five or ten metres or to a specific scenario, detector field of view modelling that accounts for cone angles, line of sight obstruction for flame detectors and open path geometric coverage, and optimisation of the voting logic across one out of N and M out of N arrangements. Geographic coverage answers what fraction of the plant volume is detected, while scenario coverage answers what fraction of credible release scenarios trigger a voted alarm within the target time. The discipline became unavoidable after incidents such as Texas City in 2005 and Caribbean Petroleum in 2009, where gas releases reached escalation even though the detector count was nominally compliant.
How the study is executed
A structured, facilitated process that runs from scope definition through close out and produces defensible, actionable outputs.
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).
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.
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.
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.
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.
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.
What the study covers in full
Outcomes of Fire and Gas Mapping (F and G Mapping)
- We surface the silent coverage gaps that prescriptive grids hide, which typically run at twenty to forty percent of credible scenarios
- We site flame detectors so they actually see through structural obstruction
- We design voting logic that survives a single detector failure or a proof test bypass
- We defend realistic detection times for your emergency shutdown activation
- Your design holds up under the ISA TR84.00.07 performance based justification
- It gives SIL claim evidence for your fire and gas safety instrumented functions to IEC 61511
- It withstands IEC 60079 29 and API RP 14C examination
- It supports FM Global, authority having jurisdiction and underwriter scrutiny on credible detection
- We reduce nuisance trip frequency through engineered voting logic
- We remove the redundant detectors that prescriptive grids accumulate
- We focus proof test scope and frequency on genuinely effective devices
- We support management of change for any plant modification that affects coverage
- You typically cut detector count by fifteen to thirty percent against a prescriptive grid with no loss of coverage
- You can defer detector replacement capital by identifying the devices that have genuinely failed
- You reduce proof test labour through a right sized detector population
- Demonstrated design rigour tightens your insurance pricing
Codes & standards we work to
Triggers that signal the need
Where Fire and Gas Mapping (F and G Mapping) applies
Wellheads, separators, gas compression, FPSO topsides, produced water systems.
Distillation columns, reactors, heat exchangers, storage spheres, LPG handling.
Cryogenic exchangers, liquefaction trains, BOG compressors, storage and sendout.
Reactive systems, batch reactors, solvent handling, runaway reaction scenarios.
Boilers, HRSGs, steam headers, hydrogen systems, ammonia SCR units.
Sterile vessels, CIP/SIP, pressure fermenters, solvent recovery, spray dryers.
Tangible deliverables
- A 3D mapping report with geographic and scenario coverage outputs
- A detector schedule with type, location, orientation and voting
- Coverage iso surface plots for each detector type
- A performance target gap analysis and closure plan
- A voting logic specification and cause and effect input
- SIL allocation and verification for the fire and gas safety instrumented functions
- Detector procurement specifications for FM and SIL certified devices
- An integration map with your safety instrumented system, emergency shutdown and HMI alarm philosophy
- A cybersecurity overlay to the IEC 62443 zone and conduit model
Ready to start your project?
Speak with our team to scope an engagement tailored to your facility, regulatory context, and lifecycle stage.