Elements with at least one edge shared among three or more elements. Legitimate multiple edges would be found at a "T" junction, where more than two geometry surfaces meet.

Groups of four triangles that form a tetrahedron with no volume element inside. This is best fixed by merging two of the nodes that would collapse the unwanted triangle box.

Elements with two single edges. These are either corners of baffles or are triangles that are protruding from a surface and are thus undesirable in the mesh.

Elements that have both single and multiple edges. These elements are probably not wanted.

Surface elements that don't share a face with a volumetric element. This could be an area with an extra surface element to be deleted or a missing volume element to be created.

Surface elements with at least one edge that isn't shared with any other surface element. This would represent a hanging edge, and the element would be an internal baffle. These may or may not be legitimate. Legitimate single edges would exist where the geometry has a zero thickness baffle with a free or hanging edge.

Tri elements with nodes that are within the circumsphere of adjacent elements. These can often be removed by swapping edges of these triangles.

Surface elements that occupy part of the same surface area, but don't have the same nodes. This could be surface mesh that folds on to itself. This will also find elements that are at an angle of up to 5 degrees from overlapping each other, as shown in the example below.

Figure 5  Example of Overlapping Element

Vertices whose adjacent elements outer edges don't form a closed loop. Usually indicates elements that jump from one surface to another, forming a "tent like" structure. This would usually pose no problem for mesh quality but will represent a barrier in the free domain that probably should not be there. See the figure in Edit Mesh > Split Mesh.

Vertices that are not connected to any element. These are usually eliminated automatically upon saving the mesh.