A Fire and Gas Mapping Study is an analysis conducted to determine the optimal placement of fire and gas detectors within industrial facilities to ensure early detection of flammable or toxic gas releases and fires, thereby enhancing safety.
The F&G (Fire and Gas) process involves identifying hazardous areas, characterizing risks, defining potential leak scenarios, and strategically placing detectors using 3D modeling to ensure effective coverage for early detection and response.
The Fire and Gas layout refers to the specific arrangement of detectors within a facility, designed to provide comprehensive coverage of all identified hazardous zones, ensuring that potential leaks or fires are detected promptly.
A comprehensive Fire & Gas Mapping Study in Oman is essential for ensuring the optimal placement of gas and flame detectors across industrial facilities. This study is critical for the design and operation of refineries, storage, and handling plants to minimize risks associated with gas releases and fires. While the goal is to maintain a plant free from such incidents, the risk is never zero. The likelihood of a release or fire varies depending on the materials involved, operating conditions, and containment methods.
Early detection of flammable or toxic gas releases and fires is key to mitigating potential disasters. In Oman, where industrial facilities are increasingly utilizing remote monitoring and automation, rapid detection through an instrumented monitoring system is crucial. This system, comprising strategically placed gas and flame detectors, enhances safety by enabling swift responses, either manually by operators or automatically through engineered systems like shutdowns and deluge systems.
Step 1: Hazardous Area Identification
The facility area will be critically assessed for identifying all hazardous areas that are present in the location into different hazardous zones.
Step 2: Hazardous Area Characterization
From the above identification, major accident hazards will be characterized based on the likelihood and frequency of the incident and based on the properties and quantity released.
Step 3: Risk Volume Definition
A representative leak size will be selected based on the standards for all the loss of containment scenarios isolated in step 2.
Step 4: Determination of characteristic cloud for detection
The identified scenarios will be modeled using software to calculate the impact distance in downwind and crosswind directions at prevalent wind conditions at the location.
Step 5: Existing Detector Layout Definition
The existing fire and gas detectors, if available at the site will be checked for maximum distance coverage using the software.
Step 6: Coverage Mapping/Detect 3D Modelling
The drawing file will be imported into the software. Existing detector and impact distance calculated will be overlaid on the 3D map to check if the existing detectors are at an adequate location to sense and detect the likely fire and gas dispersion at that location. If existing detectors are not available, new hydrocarbon/toxic detectors will be placed near the loss of containment scenarios.
Step 7: Optimization/Detector Layout Definition
Repeat the above steps for all loss of containment scenarios. Optimize the detector location height or change the place of detector location to match the dispersion coverage of the hydrocarbon /toxic release if the detectors are found inadequate to sense or detect the dispersion.
The methodology used for the study has been indicated pictorially.
Fire and Gas Mapping Methodology Flowchart
The hazardous area of this facility were identified based on the properties of the materials handled and the potential hazards in the systems which could lead to loss of containment events.
The risk from a flammable or toxic material release is the combination of the probability of a leak occurring and the potential consequences should the leak occur. In determining the probability of a leak, the type of operation, the operating conditions, and the equipment involved are all considered. In determining the consequences, the material contained, the size of the leak, the proximity of the leak to other equipment or the fence line, and the speed with which the leak might be detected without instruments are all considerations.
In the identified hazardous areas, the potentially hazardous equipment/hazardous scenarios were identified and characterized, based on that either Toxic, Flammable gas or Fire detectors will be placed.
Dispersion modelling of critical scenarios provides the basis for the detector location for minimizing the catastrophe due to release of identified flammable or toxic gas. The expected release of the hydrocarbon/toxic gas during normal or abnormal operations from potential sources due to piping leaks and dispersion of vapour/gas based on prevalent wind conditions in that location was done through the modelling. Example Dispersion graph and contour is given below.
“Risk Mapping Method” in detect 3D software was used, in line with ISA TR-84.00.07 standard, to assess the detector coverage. Adequate protection using F&GS devices shall be provided to prevent an incident from starting or from escalating.
Combination F&GS devices shall be provided at strategic locations where flammable gases or fires are likely to occur and are likely to increase the area of detectors coverage. This shall include the use of point gas detectors, open path gas detectors for both perimeter and area monitoring of flammable gases, and flame/heat detectors, or a combination thereof, for specific potential leak sources.
There are numerous factors that may affect the number and location of gas detectors. Some of the factors that shall be considered include, but are not limited to, the following:
A. Leak (hole) size, process pressures, and leak rate.
B. Type of facility being protected with gas detectors (onshore, offshore, outdoor, or indoor).
C. Density of equipment, walls, or obstructions in and around the gas detectors.
D. Vapor density of gas in the process.
E. Type of gas hazard being detected (toxic or flammable).
F. Detector technology being installed (point, open path, ultrasound).
Once the type of facility being protected with gas detection equipment, hazardous area, the minimum leak size to be detected, the type of gas hazards and its properties have been determined for locating the detectors then gas detector technology should be considered.
The following are the types of gas detection system considered for the mapping study based on the hazard associated with the facility.
