Quote - Yes, that was my Bryce Flak Freebie that you are referring to and it was constructed the same way as this explosion.  One mesh and volumetric material for the smoke and another mesh and volumetric material for the fire.  With a light in the middle of it. 

Anytime you add the volumetric material, you will have increased render time.  Add transparency and your render time increases more.  Add more lights and your render time goes up again.  Want soft shadows?  Go ahead and add them, but the render time goes up even more.

I looked in on the zip file being referred to and found the it is indeed yours, UVDan. I stand in awe. 

You are right about the increases in render time for the additions of which you speak. In addition to that, the size of the picture, (as in H x W), will affect the render time. There are also resolution settings that affect it as well. As it is, all of these things must be considered when you go to render your scene or animation. I have only done a few simple scene animations so far, due to the fact that I am working with just the one computer with 4GBs of RAM.

Stay awesome!

Agent 0013.