The µFlacs application is basically a PC-program where functions for defining, retrieving, computing and presenting gas explosion simulations have been integrated. The purpose of µFlacs is to assist the user in making correct decisions in order to estimate the damage consequences of accidental gas explosions. Its ease of use should encourage sensitivity studies for various layouts of a module or process plant.

The primary fields of usage for µFlacs are expected to be in the early design phase of new geometries where the overall design issues are addressed, and in hazards identification in existing geometries. In both of these fields µFlacs can serve as a screening tool.

µFlacs is a tool which should be used to determine how the layout of an offshore module should be: optimum positioning of equipment and optimum position of vent openings. The tool has a limited memory capacity. As a result not all obstacles (piping and equipment) can be represented. Therefore the tool cannot be used for quantitative predictions of pressure development in such complex geometries.

For detailed gas explosion simulations, µFlacs cannot replace more advanced tools such as FLACS (Flame Acceleration Simulator). The µFlacs simulator is based on the FLACS code, but µFlacs works with reduced spatial resolution to speed up computing time, it allows a simplified definition of parameters to the simulation, and the simulator is fully integrated with a graphical user interface.

Although µFlacs users should have some basic knowledge in the area of application, the relatively easy use of µFlacs will potentially make it an appropriate educational tool as well.

Details about the use of µFlacs can be found in the user guide (Torkildsen et al., 1991).

13.1 Hardware and Software Requirements

To run µFlacs you need:

• 386 PC or higher
• 4 Mbytes Ram
• Numerical co-processor
• Windows 3.0 or higher
  
  

13.2 Geometry

Most common drawing facilities are available to the user in the µFlacs graphical user interface. Previously designed geometries can be edited and new geometries designed from scratch. The µFlacs application allows you to create and edit a 3D description of a process plant. To create or edit the 3D description µFlacs uses three 2D view planes (xy, xz, yz). The xy view plane corresponds to a plan view, the xz and yz to elevation views. The view planes are properly scaled to the current application. It is possible to obtain a 3D view of the design, but the geometry cannot be edited in the 3D viewing mode.

13.3 µFlacs Validation

The validation of µFlacs has been performed by comparing µFlacs simulation results with FLACS simulation results for identical geometries and scenarios. Hence, due to the limited allowable µFlacs scenario (gas type, cloud size, concentration, output facilities...) and geometry representations (porosities, wall panel types, number of obstacles...), the FLACS input data are not as detailed and extensive as in normal FLACS applications.

15 representative offshore geometries have been chosen for comparison between the codes. Some of these geometries have been simulated as part of GexCon work, hence results from the simulations are confidential. This Section summarises the results of the comparison exercise without disclosing any information through which the modules used can be recognised or results attributed to specific modules.

The sizes of these geometries range from 1,000 m³ to 30,000 m³. Module types include process and wellhead modules, a variety of equipment number and sizes are used. Propane or methane is used as fuel. Ignition locations vary. Explosion venting varies between almost closed to three side walls open.

Figure 13.1 summarises µFlacs and FLACS simulation results in the form of maximum overpressures for the 15 modules represented in a typical µFlacs fashion (with µFlacs limitations to geometry complexity etc.).

13.4 Output from µFlacs

Figure 13.2 shows a typical output report from a µFlacs simulation.