Again messing with smoke density and Multiple Scattering off and then on. I think in coming versions of fume it would be nice to have a speedup of multiple scattering. Even with optimizing it, it still just blasts the rendering time through the roof.
Regardless of that, I was looking at fire and explosions when exposed to film and a lot of times that exposure is just almost pure white.
You can also download the file if you'd like. It's saved as a Max 2010 file: