One thing remains. The initial flash that accompanies the explosion is easily achieved in LightWave thanks to its lens flare capabilities. Add a new point light to your scene, and call it Explosion Light. Now go into the light properties (p) and make the light pure white - 255, 255, 255 - and turn on Lens Flare. We're going to set up two envelopes, one for the overall intensity of the light and one for its lens flare to get that explosion look. Click on the envelope button next to intensity first and enter these details:

Frame 1 = 0% Tension = 1
Frame 4 = 400% Tension = 0
Frame 6 = 0% Tension = 1

Should look something like this:

This makes a good glow around the explosion now, but we need to set an envelope for the Flare Intensity like so:

The figures are as follows:

Frame 2 = 0% Tension = 1
Frame 4 = 200% Tension = 0
Frame 9 = 0% Tension = 1

That should give us a nice flash of light to accompany the explosion and give a real sense of realism to your animation. I think that's about it. Go ahead and tweak the settings to see what the changes you make do to the animation. Perhaps you want it a little more billowy at the start? Maybe you want the cloud to adhere more to the shape of the column of bubbles that rises? It's all easy to do. Good luck!