12 Nov Abstract: This paper presents an under-appreciated way to conceptualize stationary black holes, which we call the river model. The river model is mathematically sound, yet simple enough that the basic picture can be understood by non-experts. %that can by understood by non-experts. In the river model. This will look through your model for any holes or areas that are not watertight. You can access this tool by going to Repair > Identify Non-Manifold Edges. This will visually highlight any problematic edges on your mesh with a bright red line. You can turn off this display at any time by going to Repair > Clear Results. The Swiss cheese model. Investigations have revealed that most industrial incidents include multiple independent failures. Imagine each layer of protection as a slice of Swiss cheese (3), with the holes representing vulnerabilities to failure (Figure 2). For an incident to occur, the holes in the slices of cheese must align.