Didn't download it.. but I'll assume it's a wall ;D
in your geometry LOD select everything...
then go to
Structure>Topology>Find Components
and however many components there are will show up in the component list .
then go to:
Structure>Convexity>Component Convex Hull
and your collision works..
you should do the same for the Fire Geo to get it workin properly as well..
if selecting the Convex Hull option deforms your model, then you should make it simpler or just make a smaller selection.
:cheers: