**1.** The general thinking is that more cube-like cells (size ratio = 1.0) are "better". I think that you start to get a greater chance of numerical artifacts or instability errors the farther away the cells are from cubes.

**2.** There are two different actors (PyroSim, and FDS) and two different cases (aligned blocks and all other geometry).

For aligned blocks, PyroSim will write the geometry to the FDS input file exactly as it has been specified. FDS will then fit the geometry to the mesh by adjusting the bounds of the geometry to hit the cell divisions.

For all other geometry, PyroSim converts it to aligned blocks when it writes the FDS input file. PyroSim uses the meshes to figure out how to do this and the geometry it writes to the FDS file will be what you get when FDS runs. It tends to look like a blocky version of what you see in PyroSim. You can click toolbar button **Preview FDS Blocks** to see what it will look like.

**3.** I've never actually thought about the relationship between particles and cells. I think they are mesh independent but I don't know for sure. I use sprinklers like it doesn't matter where they hit on the mesh.