There are two ways to handle exclusion of areas without hazards from an Effigy study.  The first (and more elegant solution) is to use the area grading.  By defining only, the leak sources as graded areas Effigy will calculate coverage results separately for each grade (A, B and C) and areas that are not graded can be safely excluded from the analysis.  In this way you can obtain a coverage result for only the areas of the process where the hazards exist.  However, some operating companies do not subscribe to the area grading philosophy, or some oddly shaped areas may need to have sections removed.  In these cases, you can exclude areas by enclosing the unwanted area or volume inside of obstructions.  This can be done by creating a cuboid (or really, any other appropriate shape) obstructions with a very small z dimension at the analysis elevation.  By doing this, you will see that this area is colored grey on the FGS layout page, indicating that it is within an obstruction at the analysis level.  Since that area is within an obstruction this will cause Effigy to ignore this area when calculating coverage.  Also note that if an entire volume needs to be removed to address an oddly shaped zone the obstruction created to “hide” the missing area can be adjusted to any volume.

See the images below for an example.

Figure 1 – 3D View of Area Removal (Purple) Via Obstruction Insertion

Figure 2 – FGS Layout View of Area (Gray) Removed via Obstruction Placement