3D Fire and Gas Mapping

Why detector placement is not intuitive

Fire and gas detectors are still routinely placed by judgement - one per area, near the equipment that looks risky. The result is predictable: some zones are covered three times over and others not at all, and nobody knows which is which until there is a release.

3D fire and gas mapping replaces that judgement with a geometric model. The plant is built in 3D with its equipment, structures and obstructions, and detector coverage is computed against it.

Two coverage questions

• Geographic coverage - what fraction of the hazardous volume can be detected at all, regardless of where a leak starts. This exposes blind spots created by vessels and structures shadowing the detectors
• Scenario coverage - for the credible release cases, would the detectors actually see the cloud given its likely direction, size and the prevailing wind

Good geographic coverage with poor scenario coverage is common, and it is the more dangerous of the two failures.

Scope

• 3D model build from plot plans, isometrics or an existing model
• Assessment of existing detector layout, where one exists
• Coverage computation for point gas, open path, flame and smoke detection
• Optimised layout with detector count, position, height and orientation
• Voting logic and alarm threshold recommendations
• Coverage targets agreed against ISA TR84.00.07 performance-based method

Usually fewer detectors, better placed

Mapping is often assumed to mean more hardware. In practice it just as often reduces the count, because it identifies detectors doing nothing that another already covers - while closing the gaps that mattered.