Fire and Gas Mapping Studies
Computer aided design to increase safety and reduce cost.
Fire and Gas Detection systems should play a crucial role in Loss Prevention on many sites. Formal Safety Assessments such as Quantified Risk Assessments (QRA) often assume that Fire and Gas Detection Systems will reduce risks, yet their design is often a matter of “black art”; it is often difficult to quantify the parameters involved and there is little guidance to define required performance or to relate achieved performance to safety requirements.
Modern fire and gas detection designs tend towards hazard based approach featuring recognized and quantified hazards, for example ranging from highly sensitive items such as hydrocarbon Gas Compressors through to lower risk items such as Produced Water Vessels.
Using highly developed assessments methods together with our custom software the FDA (Flame Detection Assessment), GDA ( Gas Detection Assessment) and HDA (Heat Detection Assessment) packages Micropack are able to review and assess arrangements from initial designs through construction and onto existing installations. The assessments are used to optimize and validate designs and maybe used in formal safety studies.
This guide has been prepared in order to define the methodology used for the completion of a fire and gas review, at both onshore and offshore sites. The methods will vary dependent on if it is an existing facility or a design review for a new facility.
Flame Detection Coverage Assessment
Flame Detection Coverage Assessment Flame Detection Coverage can be assessed using Micropack’s proprietary software based mapping tool (FDA). The input requirements for this tool are Performance Targets, Detector Layouts and details of the detector types all obtained previously. The detectors are represented as 2 dimensional Computer Aided Design (CAD) files depicting each detector’s field of view. The performance Targets for each area are set according to their local hazards and escalation risks. This information is stored in a ‘Grademap’ file. A custom software system then ‘overlays’ each relevant detector’s footprint onto the Grademap and, using a truth table, constructs a graphical image of the coverage afforded by the area’s detectors. The finished graphical file is known as the ‘assessment’ file and provides an objective estimate of that area’s flame detection coverage physical obstruction and hazard grading, an interaction that is virtually impossible visualize without computer assistance.
In the example shown below the areas shown in green meet the flame detection coverage targets, those areas in orange and yellow meet restricted targets while those in red have poor coverage and may require revision. The tabular summary provides quantitative data on the hazard coverage.
Typical Fire Detection Assessment
Gas Detection Coverage Assessment
GDA uses a number of simplifying assumptions in order to make it possible to assess sites. It is assumed that all gas detectors are either ‘point’ or ‘open path’ gas detectors, and that gas is detected if the accumulation envelopes a detector or intersects the track of an open path detector. Other types of inferential gas detector technologies including ultrasonic gas detection measures are no presently modelled by GDA, primarily because they effectively respond to release rates rather than gas concentrations.
Each area assessed is represented as a regular orthogonal volume specified in terms of its length, width and height (or, using conventional Cartesian coordinates, X, Y and Z dimensions). The assessment result is, by definition a three dimensional structure which cannot easily be rendered on two dimensional paper, and the results of the assessment are available both as a numerical summary and as a series of horizontal ‘slices’ through the volume. These slices are available at various intervals and, for clarity; one representative slice for each area will be reproduced in this study.